Chronic Renal Failure

Introduction
Background

Chronic kidney disease (CKD) is a worldwide public health problem and is now recognized as a common condition that is associated with an increased risk of cardiovascular disease and chronic renal failure (CRF).

The Kidney Disease Outcomes Quality Initiative (K/DOQI) of the National Kidney Foundation (NKF) defines chronic kidney disease as either kidney damage or a decreased kidney glomerular filtration rate (GFR) of less than 60 mL/min/1.73 m2 for 3 or more months. Whatever the underlying etiology, the destruction of renal mass with irreversible sclerosis and loss of nephrons leads to a progressive decline in GFR. The different stages of chronic kidney disease form a continuum in time; prior to February 2002, no uniform classification of the stages of chronic kidney disease existed. At that time, K/DOQI published a classification of the stages of chronic kidney disease, as follows:

* Stage 1: Kidney damage with normal or increased GFR (>90 mL/min/1.73 m2)
* Stage 2: Mild reduction in GFR (60-89 mL/min/1.73 m2)
* Stage 3: Moderate reduction in GFR (30-59 mL/min/1.73 m2)
* Stage 4: Severe reduction in GFR (15-29 mL/min/1.73 m2)
* Stage 5: Kidney failure (GFR <15 mL/min/1.73 m2 or dialysis)

In stage 1 and stage 2 chronic kidney disease, GFR alone does not clinch the diagnosis. Other markers of kidney damage, including abnormalities in the composition of blood or urine or abnormalities in imaging tests, should also be present in establishing a diagnosis of stage 1 and stage 2 chronic kidney disease.

The K/DOQI definition and the classification of chronic kidney disease allow better communication and intervention at the different stages.
Pathophysiology

Approximately 1 million nephrons are present in each kidney, each contributing to the total GFR. Regardless of the etiology of renal injury, with progressive destruction of nephrons, the kidney has an innate ability to maintain GFR by hyperfiltration and compensatory hypertrophy of the remaining healthy nephrons. This nephron adaptability allows for continued normal clearance of plasma solutes so that substances such as urea and creatinine start to show significant increases in plasma levels only after total GFR has decreased to 50%, when the renal reserve has been exhausted. The plasma creatinine value will approximately double with a 50% reduction in GFR. A rise in plasma creatinine from a baseline value of 0.6 mg/dL to 1.2 mg/dL in a patient, although still within the reference range, actually represents a loss of 50% of functioning nephron mass.

The residual nephron hyperfiltration and hypertrophy, although beneficial for the reasons noted, has been hypothesized to represent a major cause of progressive renal dysfunction. This is believed to occur because of increased glomerular capillary pressure, which damages the capillaries and leads initially to focal and segmental glomerulosclerosis and eventually to global glomerulosclerosis. This hypothesis has been based on studies of five-sixths nephrectomized rats, which develop lesions that are identical to those observed in humans with chronic kidney disease.

Factors other than the underlying disease process and glomerular hypertension that may cause progressive renal injury include the following:

* Systemic hypertension
* Acute insults from nephrotoxins or decreased perfusion
* Proteinuria
* Increased renal ammoniagenesis with interstitial injury
* Hyperlipidemia
* Hyperphosphatemia with calcium phosphate deposition
* Decreased levels of nitrous oxide
* Smoking

Frequency
United States

In the United States, there is a rising incidence and prevalence of kidney failure, with poor outcomes and high cost. Kidney disease is the ninth leading cause of death in the United States. Data from the United States Renal Data System (USRDS) indicated that there has been an increase of 104% in the prevalence of chronic renal failure (CRF) between the years 1990-2001. There is an even higher prevalence of the earlier stages of chronic kidney disease.

According to the Third National Health and Nutrition Examination Survey, it was estimated that 6.2 million people (ie, 3% of total US population) older than 12 years had a serum creatinine value above 1.5 mg/dL; 8 million people had a glomerular filtration rate (GFR) of less than 60 mL/min, the majority of them being in the Medicare senior population (5.9 million people). Therefore, for the first time, the US Surgeon General's mandate for America's citizenry, Healthy People 2010, contains a chapter focused on chronic kidney disease. The objectives of this chapter are to articulate goals and to provide strategies to reduce the incidence, morbidity, mortality, and health costs of chronic kidney disease in the United States. The burden of chronic kidney disease can be assessed by multiple criteria, all of which underscore the need for improved detection, treatment, and monitoring of clinical and fiscal outcomes. Reducing renal failure will require additional public health efforts, including effective preventive strategies and early detection and treatment of chronic kidney disease.

Because of the nonuniform definition of kidney disease prior to February 2002, among other factors, most patients with earlier stages of chronic kidney disease have not been recognized or adequately treated. The Third National Health and Examination Survey (NHANES III) estimated that the prevalence of chronic kidney disease in adults in the United States was 11% (19.2 million): 3.3% (5.9 million) had stage 1, 3% (5.3 million) had stage 2, 4.3% (7.6 million) had stage 3, 0.2% (400,000) had stage 4, and 0.2% (300,000) had stage 5.

Furthermore, the prevalence of chronic kidney disease stages 1-4 increased from 10% in 1988-1994 to 13.1% in 1999-2004. This increase is partially explained by the increase in the prevalence of diabetes and hypertension, the two most common causes of chronic kidney disease.
International

The incidence rates of end-stage renal disease (ESRD) have increased steadily internationally since 1989. The United States has the highest incident rate of ESRD, followed by Japan. Japan has the highest prevalence per million population, with the United States taking second place.
Mortality/Morbidity

Chronic kidney disease is a major cause of morbidity and mortality, particularly at the later stages. Although the diabetic population is at highest risk, in the United States, the general hemodialysis and peritoneal dialysis populations have 2 hospital admissions per patient per year; patients who have a renal transplant have an average of 1 hospital admission per year. The 5-year survival rate for a patient undergoing chronic dialysis in the United States is approximately 35%. This is approximately 25% in patients with diabetes. The most common cause of death in the dialysis population is cardiovascular disease.

Among patients with ESRD aged 65 years and older, the mortality rates are 6 times higher than in the general population. In 2003, over 69,000 dialysis patients enrolled in the ESRD program died (annual adjusted mortality rate of 210.7 per 1000 patient-years at risk for the dialysis population, which represents a 14% decrease since peaking at 244.5 per 1000 patient-years in 1988). The highest mortality rate is within the first 6 months of initiating dialysis, which then tends to improve over the next 6 months, before increasing gradually over the next 4 years.

The mortality rates associated with hemodialysis are striking and indicate that the life expectancy of patients entering into hemodialysis is markedly shortened. At every age, patients with ESRD on dialysis have significantly increased mortality when compared with nondialysis patients and individuals without kidney disease. At age 60 years, a healthy person can expect to live for more than 20 years, whereas the life expectancy of a 60-year-old patient starting hemodialysis is closer to 4 years.
Race

* Chronic kidney disease affects all races, but, in the United States, a significantly higher incidence of ESRD exists in blacks as compared to whites; the incident rate for blacks is nearly 4 times that for whites.

Sex

* In NHANES III, the distribution of estimated GFRs for the chronic kidney disease stages was similar in both sexes. Nonetheless, the USRDS 2004 Annual Data Report reveals that the incident rate of ESRD cases is higher for males with 409 per million population in 2002 compared to 276 for females.

Age

Chronic kidney disease is found in persons of all ages. The normal annual mean decline in the GFR with age from the peak GFR (approximately 120 mL/min/1.73 m2) attained during the third decade of life is approximately 1 mL/min/y/1.73 m2, reaching a mean value of 70 mL/min/1.73 m2 at age 70 years. Nonetheless, in the United States, the highest incidence rate of ESRD occurs in patients older than 65 years. As per NHANES III data, the prevalence of chronic kidney disease was 37.8% among patients older than 70 years. Besides diabetes mellitus and hypertension, age is an independent major predictor of chronic kidney disease. The geriatric population is the most rapidly growing kidney failure (chronic kidney disease stage 5) population in the United States.

The biologic process of aging initiates various structural and functional changes within the kidney. Renal mass progressively declines with advancing age. Glomerulosclerosis leads to a decrease in renal weight. Histologic examination is notable for a decrease in glomerular number of as much as 30-50% by age 70 years.

Ischemic obsolescence of cortical glomeruli is predominant, with relative sparing of the renal medulla. Juxtamedullary glomeruli see a shunting of blood from the afferent to efferent arterioles, resulting in redistribution of blood flow favoring the renal medulla. These anatomical and functional changes in renal vasculature appear to contribute to an age-related decrease in renal blood flow. Renal hemodynamic measurements in aged human and animals suggest that altered functional response of the renal vasculature may be an underlying factor in diminished renal blood flow and increased filtration noted with progressive renal aging. The vasodilatory response is blunted in the elderly when compared to younger patients. However, the vasoconstrictor response to intrarenal angiotensin is identical in both young and older human subjects. A blunted vasodilatory capacity with appropriate vasoconstrictor response may indicate that the aged kidney is in a state of vasodilatation to compensate for the underlying sclerotic damage.

Given the histologic evidence for nephronal senescence with age, a decline in the GFR is expected. However, a wide variation in the rate of decline in the GFR is reported because of measurement methods, race, gender, genetic variance, and other risk factors for renal dysfunction. Because of these anatomical and physiological changes, elderly patients with chronic kidney disease may behave differently, in terms of progression and response to pharmacological treatment, than younger patients.

Therefore, a serum creatinine value of 1.2 mg/dL in a 70-kg, 25-year-old man versus a 70-kg, 80-year-old man represents an eGFR of 74 mL/min/1.73m2 and 58 mL/min/1.73m2, respectively. What can appear as only mild renal impairment in a 70-kg, 80-year-old man with a pathologically elevated serum creatinine of 2 mg/dL actually represents severe renal impairment when the eGFR is calculated to be 32 mL/min/1.73m2. Therefore, an eGFR must be determined simply by using the Modification of Diet in Renal Disease (MDRD) equation (see Other Tests) in elderly people so that appropriate drug dosing adjustments can be made and nephrotoxins can be avoided in patients who have more extensive chronic kidney disease than would be suggested by the serum creatinine value alone.
Clinical
History

Patients with chronic kidney disease stages 1-3 (GFR >30 mL/min) are generally asymptomatic and do not experience clinically evident disturbances in water or electrolyte balance or endocrine/metabolic derangements. Generally, these disturbances clinically manifest with chronic kidney disease stages 4-5 (GFR <30 mL/min). Uremic manifestations in patients with chronic kidney disease stage 5 are believed to be primarily secondary to an accumulation of toxins, the identity of which is generally not known.

The ability to maintain potassium (K) excretion at near normal levels is generally maintained in chronic kidney disease patients as long as both aldosterone secretion and distal flow are maintained. Another defense against potassium retention in patients with chronic kidney disease is increased potassium excretion in the GI tract, which also is under control of aldosterone.

Therefore, hyperkalemia usually develops when the GFR falls to less than 20-25 mL/min because of the decreased ability of the kidneys to excrete potassium. It can be observed sooner in patients who ingest a potassium-rich diet or if serum aldosterone levels are low, such as in type IV renal tubular acidosis commonly observed in people with diabetes or with use of angiotensin-converting enzyme (ACE) inhibitors or nonsteroidal anti-inflammatory drugs (NSAIDs). Hyperkalemia in chronic kidney disease can be aggravated by an extracellular shift of potassium, such as that occurs in the setting of acidemia or from lack of insulin. Hypokalemia is uncommon but can develop among patients with very poor intake of potassium, gastrointestinal or urinary loss of potassium, diarrhea, or diuretic use.

Metabolic acidosis often is mixed, normal anion gap and increased anion gap, the latter observed generally with chronic kidney disease stage 5 but with the anion gap generally not higher than 20 mEq/L. In chronic kidney disease, the kidneys are unable to produce enough ammonia in the proximal tubules to excrete the endogenous acid into the urine in the form of ammonium. In chronic kidney disease stage 5, accumulation of phosphates, sulphates, and other organic anions are the cause of the increase in anion gap. Metabolic acidosis has been shown to have deleterious effects on protein balance, leading to a negative nitrogen balance, increased protein degradation, increased essential amino acid oxidation, reduced albumin synthesis, and a lack of adaptation to a low protein diet. Hence, this is associated with protein-energy malnutrition, loss of lean body mass, and muscle weakness. The mechanism for reducing protein may include effects on ATP-dependent ubiquitin proteasomes and increased activity of branched chain keto acid dehydrogenases.
In the NHANES III prevalence study, hypoalbuminemia (a marker of protein-energy malnutrition and a powerful predictive marker of mortality in dialysis patients as well as in the general population) was independently associated with low bicarbonate as well as the inflammatory marker C reactive protein. Metabolic acidosis is a factor in the development of renal osteodystrophy, as bone acts as a buffer for excess acid, with resultant loss of mineral. Acidosis may interfere with vitamin D metabolism, and patients who are persistently more acidotic are more likely to have osteomalacia or low-turnover bone disease. The evidence for the benefits and risks of correcting metabolic acidosis is very limited with no randomized controlled trials in pre-ESRD patients, none in children, and only 3 small trials in dialysis patients. These trials suggest that there may be some beneficial effects on both protein metabolism and bone metabolism, but the trials were underpowered to provide robust evidence. Experts recommend alkali therapy to maintain the serum bicarbonate concentration above 22 mEq/L.

Inflammation and hemostasis may increase the risk of kidney function decline, but prospective studies are lacking. The Atherosclerosis Risk in Communities (ARIC) Study, a prospective observational cohort, observed markers of inflammation and hemostasis in 14,854 middle-aged adults.1 The risk for decreased kidney function associated with the inflammatory and hemostasis markers was examined, using data from 1787 cases of chronic kidney disease (CKD) that developed between 1987 and 2004. After adjusting for various factors, such as demographics smoking, blood pressure, diabetes, lipid levels, prior myocardial infarction (MI), antihypertensive use, and alcohol use, the study revealed that the risk for chronic kidney disease rose with increasing quartiles of white blood cell (WBC) count, fibrinogen, von Willebrand factor, and factor VIIIc. The investigators found a strong inverse association between serum albumin level and chronic kidney disease risk. The study's findings suggested that inflammation and hemostasis are antecedent pathways for chronic kidney disease.

Salt and water handling by the kidney is altered in patients with chronic kidney disease. Extracellular volume expansion and total-body volume overload results from failure of sodium and free water excretion. This generally becomes clinically manifested when the GFR falls to less than 10-15 mL/min, when compensatory mechanisms have become exhausted. As kidney function declines further, sodium retention and extracellular volume expansion lead to peripheral and, not uncommonly, pulmonary edema and hypertension. At a higher GFR, excess sodium and water intake could result in a similar picture if the ingested amounts of sodium and water exceed the available potential for compensatory excretion.

Normochromic normocytic anemia principally develops from decreased renal synthesis of erythropoietin, the hormone responsible for bone marrow stimulation for red blood cell (RBC) production. It starts early in the course of disease and becomes more severe as the GFR progressively decreases with the availability of less viable renal mass. No reticulocyte response occurs. RBC survival is decreased, and tendency of bleeding is increased from the uremia-induced platelet dysfunction. Other causes of anemia in chronic kidney disease patients include chronic blood loss, secondary hyperparathyroidism, inflammation, nutritional deficiency, and accumulation of inhibitors of erythropoiesis.

Anemia is associated with fatigue, reduced exercise capacity, impaired cognitive and immune function, and reduced quality of life. Anemia is also associated with the development of cardiovascular disease, the new onset of heart failure, or the development of more severe heart failure. Anemia is associated with increased cardiovascular mortality.

Renal bone disease is a common complication of chronic kidney disease and results in both skeletal complications (eg, abnormality of bone turnover, mineralization, linear growth) and extraskeletal complications (eg, vascular or soft tissue calcification). Different types of bone disease occur with chronic kidney disease, as follows: (1) high turnover bone disease due to high parathyroid hormone (PTH) levels; (2a) low turnover bone disease (adynamic bone disease); (2b) defective mineralization (osteomalacia); (3) mixed disease; and (4) beta-2-microglobulin associated bone disease.

Secondary hyperparathyroidism develops because of hyperphosphatemia, hypocalcemia, decreased renal synthesis of 1,25-dihydroxycholecalciferol (1,25-dihydroxyvitamin D, or calcitriol), intrinsic alteration in the parathyroid gland that give rises to increased PTH secretion as well as increased parathyroid growth, and skeletal resistance to PTH.

* Calcium and calcitriol are primary feedback inhibitors; hyperphosphatemia is a stimulus to PTH synthesis and secretion.
* Phosphate retention begins in early chronic kidney disease; when the GFR falls, less phosphate is filtered and excreted, but serum levels do not rise initially because of increased PTH secretion, which increases renal excretion. As the GFR falls toward chronic kidney disease stages 4-5, hyperphosphatemia develops from the inability of the kidneys to excrete the excess dietary intake. Hyperphosphatemia suppresses the renal hydroxylation of inactive 25-hydroxyvitamin D to calcitriol, so serum calcitriol levels are low when the GFR is less than 30 mL/min. Increased phosphate concentration also effects PTH concentration by its direct effect on parathyroid gland (posttranscriptional effect).
* Hypocalcemia develops primarily from decreased intestinal calcium absorption because of low plasma calcitriol levels and possibly from calcium binding to elevated serum levels of phosphate.
* Low serum calcitriol levels, hypocalcemia, and hyperphosphatemia have all been demonstrated to independently trigger PTH synthesis and secretion. As these stimuli persist in chronic kidney disease, particularly in the more advanced stages, PTH secretion becomes maladaptive and the parathyroid glands, which initially hypertrophy, become hyperplastic. The persistently elevated PTH levels exacerbate hyperphosphatemia from bone resorption of phosphate.
* If serum levels of PTH remain elevated, a high bone turnover lesion, known as osteitis fibrosa, develops. This is one of several bone lesions, which as a group are commonly known as renal osteodystrophy. These lesions develop in patients with severe chronic kidney disease and are common in those with ESRD.
* The prevalence of adynamic bone disease in the United States has increased, and it has been described before the initiation of dialysis in some cases. The pathogenesis of adynamic bone disease is not well defined, but several factors may contribute, including high calcium load, use of vitamin D sterols, increasing age, previous corticosteroid therapy, peritoneal dialysis, and increased level of N-terminally truncated PTH fragments. Low turnover osteomalacia in the setting of chronic kidney disease is associated with aluminum accumulation and is markedly less common. Dialysis-related amyloidosis from beta-2-microglobulin accumulation in patients who have required chronic dialysis for at least 8-10 years is another form of bone disease that manifests with cysts at the ends of long bones.

Other manifestations of uremia in ESRD, many of which are more likely in patients who are inadequately dialyzed, include the following:

* Pericarditis - Can be complicated by cardiac tamponade, possibly resulting in death.
* Encephalopathy - Can progress to coma and death
* Peripheral neuropathy
* Restless leg syndrome
* GI symptoms - Anorexia, nausea, vomiting, diarrhea
* Skin manifestations - Dry skin, pruritus, ecchymosis
* Fatigue, increased somnolence, failure to thrive
* Malnutrition
* Erectile dysfunction, decreased libido, amenorrhea
* Platelet dysfunction with tendency to bleeding

Physical

The physical examination often is not very helpful but may reveal findings characteristic of the condition underlying chronic kidney disease (eg, lupus, severe arteriosclerosis, hypertension) or complications of chronic kidney disease (eg, anemia, bleeding diathesis, pericarditis).
Causes

* Vascular disease - Renal artery stenosis, cytoplasmic pattern antineutrophil cytoplasmic antibody (C-ANCA)–positive and perinuclear pattern antineutrophil cytoplasmic antibody (P-ANCA)–positive vasculitides, antineutrophil cytoplasmic antibody (ANCA)–negative vasculitides, atheroemboli, hypertensive nephrosclerosis, renal vein thrombosis
* Primary glomerular disease - Membranous nephropathy, immunoglobulin A (IgA) nephropathy, focal and segmental glomerulosclerosis (FSGS), minimal change disease, membranoproliferative glomerulonephritis, rapidly progressive (crescentic) glomerulonephritis
* Secondary glomerular disease - Diabetes mellitus, systemic lupus erythematosus, rheumatoid arthritis, mixed connective tissue disease, scleroderma, Goodpasture syndrome, Wegener granulomatosis, mixed cryoglobulinemia, postinfectious glomerulonephritis, endocarditis, hepatitis B and C, syphilis, human immunodeficiency virus (HIV), parasitic infection, heroin use, gold, penicillamine, amyloidosis, light chain deposition disease, neoplasia, thrombotic thrombocytopenic purpura (TTP), hemolytic-uremic syndrome (HUS), Henoch-Schönlein purpura, Alport syndrome, reflux nephropathy
* Tubulointerstitial disease - Drugs (eg, sulfa, allopurinol), infection (viral, bacterial, parasitic), Sjögren syndrome, chronic hypokalemia, chronic hypercalcemia, sarcoidosis, multiple myeloma cast nephropathy, heavy metals, radiation nephritis, polycystic kidneys, cystinosis
* Urinary tract obstruction - Urolithiasis, benign prostatic hypertrophy, tumors, retroperitoneal fibrosis, urethral stricture, neurogenic bladder
* See related CME at Guidelines for Hepatitis C in Chronic Kidney Disease Issued.
Differential Diagnoses

Acute Renal Failure
Workup
Laboratory Studies

* Serum electrolytes, BUN, and creatinine - The BUN and creatinine levels will be elevated in patients with chronic kidney disease. Hyperkalemia or low bicarbonate levels may be present in patients with chronic kidney disease.
* Serum calcium, phosphate, vitamin D, and intact parathyroid hormone (PTH) levels are obtained to look for evidence of renal bone disease.
* CBC count - Normochromic normocytic anemia is commonly seen in chronic kidney disease. Other underlying causes of anemia should be ruled out.
* Serum albumin - Patients may have hypoalbuminemia due to urinary protein loss or malnutrition.
* Lipid profile - A lipid profile should be performed in all patients with chronic kidney disease because of their increased risk of cardiovascular disease.
* Urinalysis - Dipstick proteinuria may suggest a glomerular or tubulointerstitial problem. The urine sediment finding of RBCs, RBC casts, suggests proliferative glomerulonephritis. Pyuria and/or WBC casts are suggestive of interstitial nephritis (particularly if eosinophiluria is present) or urinary tract infection.
* Spot urine collection for total protein-to-creatinine ratio allows reliable approximation (extrapolation) of total 24-hour urinary protein excretion. A value of greater than 2 g is considered to be within the glomerular range, and a value of greater than 3-3.5 g is within the nephrotic range; less than 2 is characteristic of tubulointerstitial problems.
* Twenty-four–hour urine collection for total protein and CrCl
* In certain cases, the following tests may be ordered as part of the evaluation of patients with chronic kidney disease:
o Serum and urine protein electrophoresis to screen for a monoclonal protein possibly representing multiple myeloma
o Antinuclear antibodies (ANA), double-stranded DNA antibody levels to screen for systemic lupus erythematosus
o Serum complement levels - May be depressed with some glomerulonephritides
o C-ANCA and P-ANCA levels - Helpful if positive in diagnosis of Wegener granulomatosis and polyarteritis nodosa or microscopic polyangiitis, respectively
o Anti–glomerular basement membrane (anti-GBM) antibodies - Highly suggestive of underlying Goodpasture syndrome
o Hepatitis B and C, HIV, Venereal Disease Research Laboratory (VDRL) serology - Conditions associated with some glomerulonephritides

Imaging Studies

* Plain abdominal x-ray - Particularly useful to look for radio-opaque stones or nephrocalcinosis
* Intravenous pyelogram - Not commonly used because of potential for intravenous contrast renal toxicity; often used to diagnose renal stones
* Renal ultrasound - Small echogenic kidneys are observed in advanced renal failure. Kidneys usually are normal in size in advanced diabetic nephropathy, where affected kidneys initially are enlarged from hyperfiltration. Structural abnormalities, such as polycystic kidneys, also may be observed. This is a useful test to screen for hydronephrosis, which may not be observed in early obstruction, or involvement of the retroperitoneum with fibrosis, tumor, or diffuse adenopathy. Retrograde pyelogram may be indicated if a high index of clinical suspicion for obstruction exists despite a negative study finding.
* Renal radionuclide scan - Useful to screen for renal artery stenosis when performed with captopril administration but is unreliable for GFR of less than 30 cc/min; also quantitates differential renal contribution to total GFR
* CT scan - CT scan is useful to better define renal masses and cysts usually noted on ultrasound. Also, it is the most sensitive test for identifying renal stones. IV contrast-enhanced CT scans should be avoided in patients with renal impairment to avoid acute renal failure; this risk significantly increases in patients with moderate-to-severe chronic kidney disease. Dehydration also markedly increases this risk.
* MRI is very useful in patients who require a CT scan but who cannot receive intravenous contrast. It is reliable in the diagnosis of renal vein thrombosis, as are CT scan and renal venography. Magnetic resonance angiography also is becoming more useful for diagnosis of renal artery stenosis, although renal arteriography remains the criterion standard.
* Voiding cystourethrogram (VCUG) - Criterion standard for diagnosis of vesicoureteral reflux

Other Tests

* The Cockcroft-Gault formula for estimating CrCl should be used routinely as a simple means to provide a reliable approximation of residual renal function in all patients with chronic kidney disease. The formulas are as follows:
o CrCl (male) = ([140-age] X weight in kg)/(serum creatinine X 72)
o CrCl (female) = CrCl (male) X 0.85
* Alternatively, the Modification of Diet in Renal Disease (MDRD) Study equation could be used to calculate the GFR. This equation does not require a patient's weight.2

Procedures

* Percutaneous renal biopsy is performed most often with ultrasound guidance and the use of a mechanical gun. It generally is indicated when renal impairment and/or proteinuria approaching the nephrotic range are present and the diagnosis is unclear after appropriate other workup. It is not indicated in the setting of small echogenic kidneys on ultrasound because these are severely scarred and represent chronic irreversible injury. The most common complication of this procedure is bleeding, which can be life threatening in a minority of occurrences.
* Surgical open renal biopsy can be considered when the risk of renal bleeding is felt to be great, occasionally with solitary kidneys, or when percutaneous biopsy is technically difficult to perform.

Histologic Findings

Renal histology in chronic kidney disease reveals findings compatible with the underlying primary renal diagnosis and, generally, findings of segmental and globally sclerosed glomeruli and tubulointerstitial atrophy, often with tubulointerstitial mononuclear infiltrates.
Treatment
Medical Care

The medical care of patients with chronic kidney disease should focus on the following:

* Delaying or halting the progression of chronic kidney disease
o Treatment of the underlying condition if possible
o Aggressive blood pressure control to target values per current guidelines. Systolic blood pressure control is considered more important and is also considered difficult to control in elderly patients with chronic kidney disease.
o Use of ACE inhibitors or angiotensin receptor blockers as tolerated, with close monitoring for renal deterioration and for hyperkalemia (avoid in advanced renal failure, bilateral renal artery stenosis [RAS], RAS in a solitary kidney). Data support the use of ACE inhibitors/angiotensin receptor blockers in diabetic kidney disease with or without proteinuria. However, in nondiabetic kidney disease, ACE inhibitors/angiotensin receptor blockers are effective in retarding the progression of disease among patients with proteinuria of less of than 500 mg/d.
o Aggressive glycemic control per the American Diabetes Association (ADA) recommendations (target HbA1C <7%)
o Protein restriction - Although the Modification of Diet in Renal Disease (MDRD) Study failed to show the effect of protein restriction in retardation of the progression of kidney disease, a meta-analysis suggests a beneficial role for protein restriction. The National Kidney Foundation (NKF) guidelines suggest that if a patient is started on protein restriction, the physician needs to closely monitor the patient's nutritional status. Predialysis low serum albumin is associated with a poor outcome among dialysis patients.
o Treatment of hyperlipidemia to target levels per current guidelines
o Avoidance of nephrotoxins - IV radiocontrast, nonsteroidal anti-inflammatory agents, aminoglycosides
o Encourage smoking cessation, as smokers tend to reach ESRD earlier than nonsmokers.
* Treating the pathologic manifestations of chronic kidney disease, including the following:
o Anemia with erythropoietin, with the goal being 11-12 g/dL, as normalization of hemoglobin in patients with chronic kidney disease stages 4-5 has been associated with an increased risk of combined outcome. Before starting Epogen, iron stores should be checked, and the aim is to keep iron saturation at 30-50% and ferritin at 200-500.
o Hyperphosphatemia with dietary phosphate binders and dietary phosphate restriction
o Hypocalcemia with calcium supplements with or without calcitriol
o Hyperparathyroidism with calcitriol or vitamin D analogs
o Volume overload with loop diuretics or ultrafiltration
o Metabolic acidosis with oral alkali supplementation
o Uremic manifestations with chronic renal replacement therapy (hemodialysis, peritoneal dialysis, or renal transplantation): Indications include severe metabolic acidosis, hyperkalemia, pericarditis, encephalopathy, intractable volume overload, failure to thrive and malnutrition, peripheral neuropathy, intractable gastrointestinal symptoms, and the GFR less than 10 mL/min.
o Cardiovascular complications
* Timely planning for chronic renal replacement therapy
o Early education regarding natural disease progression, different dialytic modalities, renal transplantation, patient option to refuse or discontinue chronic dialysis
o Timely placement of permanent vascular access (arrange for surgical creation of primary arteriovenous fistula, if possible, and preferably at least 6 months in advance of anticipated date of dialysis)
o Timely elective peritoneal dialysis catheter insertion
o Timely referral for renal transplantation

Consultations

* Early nephrology referral (decreases morbidity and mortality)
* Renal dietitian
* Vascular surgery for permanent vascular access
* General surgery for peritoneal catheter placement
* Referral to renal transplant center

Diet

* Protein restriction early in chronic kidney disease as a means to delay a decline in the GFR is controversial; however, as the patient approaches chronic kidney disease stage 5, this is recommended to delay the onset of uremic symptoms. Patients with chronic kidney disease who already are predisposed to becoming malnourished are at higher risk for malnutrition with overly aggressive protein restriction. Malnutrition is a well-established predictor of increased morbidity and mortality in the ESRD population and must be avoided if possible.
* Phosphate restriction starting early in chronic kidney disease
* Potassium restriction
* Sodium and water restriction as needed to avoid volume overload
* See related CME at New Guidelines Address Nutritional Needs of Children With Chronic Kidney Disease.

Medication
Phosphate-lowering agents

Hyperphosphatemia is treated with dietary phosphate binders and dietary phosphate restriction. Hypocalcemia is treated with calcium supplements and possibly calcitriol. Hyperparathyroidism is treated with calcitriol or vitamin D analogs.
Follow-up
Further Inpatient Care

* Patients who develop potentially life-threatening complications of chronic kidney disease should be hospitalized and closely monitored.

Further Outpatient Care

* Patients with chronic kidney disease should be referred to a nephrologist early in the course of their disease and have continued nephrologic follow-up until initiation of chronic renal replacement therapy.
* A multidisciplinary approach to care, including involvement of the nephrologist, primary care physician, renal dietitian, nurse, and social worker, should be initiated early in the course of chronic kidney disease, with close patient follow-up.

Transfer

* Patients with chronic kidney disease acutely presenting with indications for dialytic therapy should be transferred to a hospital center where acute dialysis can be performed.

Prognosis

* Patients with chronic kidney disease generally progress to ESRD. The rate of progression depends on the underlying diagnosis, on the successful implementation of secondary preventative measures, and on the individual patient.
* Patients on chronic dialysis have a high incidence of morbidity and mortality.
* Patients with ESRD who undergo renal transplantation survive longer than those on chronic dialysis.

Patient Education

* Patients with chronic kidney disease should be educated about the importance of compliance with secondary preventative measures, natural disease progression, prescribed medications (highlighting their potential benefits and adverse effects), avoidance of nephrotoxins, diet, chronic renal replacement modalities, including peritoneal dialysis, hemodialysis, and transplantation, and permanent vascular access options for hemodialysis.
* For excellent patient education resources, visit eMedicine's Diabetes Center. Also, see eMedicine's patient education article Chronic Kidney Failure.

Miscellaneous
Medicolegal Pitfalls

* Early diagnosis and treatment of the underlying cause or/and institution of secondary preventative measures in chronic kidney disease is imperative to try to delay, or possibly halt, progression. Early nephrologic referral is of extreme importance.
* Timely initiation of chronic renal replacement therapy is imperative to prevent the uremic complications of chronic kidney disease that can lead to significant morbidity and death.
* In chronic kidney disease, doses and intervals of drugs that are excreted or metabolized renally should be adjusted accordingly for the residual GFR. Some drugs are contraindicated in moderate-to-severe renal impairment because of potentially serious effects from drug or metabolite accumulation. Routine consultation of the appropriate references should be undertaken when prescribing any new drug to a patient with chronic kidney disease.

Special Concerns

* Female patients with advanced chronic kidney disease commonly develop menstrual irregularities; women with ESRD are typically amenorrheic and infertile.
* Pregnancy in chronic kidney disease can be associated with accelerated renal decline. In advanced chronic kidney disease and ESRD, pregnancy is associated with markedly decreased fetal survival.