- Author: A Brent Alper, Jr, MD, MPH; Chief Editor: Vecihi Batuman, MD, FACP, FASN more...
The diagnosis of renal failure is based primarily on an abnormal glomerular filtration rate (GFR) or abnormal creatinine clearance, which is usually evident due to an elevated serum creatinine level. GFR determination can be accomplished by 24-hour urine collection for creatinine clearance, although this is often cumbersome and inaccurate due to improper collection.
It is very important to determine if the kidney failure is acute or chronic, as acute kidney injury likely is reversible if treated properly. Review of the patient's history and of previous laboratory values can be very helpful in this regard.
Other blood studies to consider for abnormalities prevalent with clinical uremia include the following:
Urinalysis with microscopic examination should be performed on all patients to evaluate for the presence of protein, cellular casts, oval fat bodies, ketones, hemoglobin, and myoglobin, and to assess pH.
The assessment of nuclear medicine radioisotope (iothalamate) clearance is the criterion standard for measuring GFR. However, this test is time consuming and is more expensive than estimating GFR using either the Modification of Diet in Renal Disease (MDRD) formula or the Cockcroft-Gault formula.
In premenopausal females and prepubertal patients, begin the workup for anemia when the hemoglobin level is less than 11 g/dL or the hematocrit value is less than 33%. In men and postmenopausal women, begin the workup when the hemoglobin level is less than 12 g/dL or the hematocrit value is less than 37%.
Glomerular Filtration Rate
All patients with an abnormal creatinine clearance should have their GFR estimated using one of several formulas that employ easily obtainable values, such as the MDRD or Cockcroft-Gault formula. Both formulas have been shown to provide similar values within a wide range of patient ages and to be accurate in patients with renal insufficiency, regardless of race or sex.
Staging is determined by the GFR (creatinine clearance). Currently, the National Kidney Foundation no longer recognizes the terms chronic renal insufficiency (CRI) or chronic kidney disease (CKD), but rather it recognizes the 5 stages of CKD based on the estimated GFR (eGFR), as calculated by the MDRD formula. These stages are as follows:
Stage 1 - Kidney damage with normal GFR, 90 mL/min or greater
Stage 2 - Kidney damage with a mild decrease in GFR, 60-89 mL/min
Stage 3 - Kidney damage with a moderate decrease in GFR, 30-59 mL/min
Stage 4 - Kidney damage with a severe decrease in GFR, 15-29 mL/min
Stage 5 - End-stage renal disease, GFR less than 15 mL/min or patient on dialysis
A renal ultrasonographic study is indicated to evaluate for hydronephrosis or obstruction. Hydronephrosis can occur with ureteral or bladder obstruction, retroperitoneal fibrosis, massive abdominal tumors due to cervical or prostate cancers, or other structural abnormalities.
Renal ultrasonography is also performed to determine the size and shape of the kidneys. Large kidneys are associated with diseases such as early diabetic nephropathy, multiple myeloma, polycystic kidney disease, and human immunodeficiency virus (HIV)–associated glomerulonephritis. Small kidneys usually indicate chronic, irreversible damage from diseases such as hypertensive nephrosclerosis, ischemic nephropathy, or any other long-standing kidney disease.
CT Scanning and MRI
Consider a brain computed tomography (CT) scan in the event of a significant change in the patient’s mental status, especially if the change occurs after a fall or in association with mild trauma. Spontaneous subdural hematomas occur in patients with uremia, particularly if the BUN level is greater than 150-200 mg/dL.
CT scanning of the abdomen may be indicated to rule out retroperitoneal fibrosis, pelvic masses, lymphadenopathy, or lymphoma if bilateral hydronephrosis is found on ultrasonographic images and no obvious etiology is present (eg, stone, bladder mass, ureteral mass).
Magnetic resonance imaging (MRI) arteriograms can be used to assess the kidneys for renal artery stenosis, acute arterial thrombosis, or aortic dissection involving the aorta and renal arteries. It is important to consider renal artery stenosis in the differential diagnosis because it is one cause of renal failure that is potentially reversible by angioplasty or bypass surgery of the affected renal artery.
A renal biopsy is necessary to make an accurate diagnosis of acute kidney injury (AKI) or chronic kidney disease (CKD). However, if the renal failure has been slowly progressive and the kidneys are small, renal biopsy results are of little benefit. In the setting of uremia, performing a renal biopsy in a patient with small kidneys may be dangerous because of comorbid disease and the increased risk of bleeding.
In the setting of rapidly progressive renal failure or AKI of unknown etiology, a renal biopsy is indicated to determine whether potentially reversible or treatable renal disorders are present.
Histologic findings vary depending on the underlying etiology. However, in the setting of late-stage CKD and uremia in which renal function has deteriorated over a prolonged period and the kidneys are relatively small, renal biopsy results may show significant glomerulosclerosis and obsolescent glomeruli (completely scarred and sclerosed) with significant interstitial fibrosis. These findings are nonspecific and do not aid in determining the underlying cause of renal failure.
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