Approach Considerations
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. Although assessment of nuclear medicine radioisotope (iothalamate) clearance is the criterion standard for measuring GFR, this test is time consuming and expensive. GFR determination can be accomplished by 24-hour urine collection for creatinine clearance, but this is often cumbersome and inaccurate due to improper collection. In practice, the estimated glomerular filtration rate (eGFR) is most often used.
It is very important to determine whether 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:
-
Hemoglobin
-
Calcium
-
Phosphate
-
Parathyroid hormone
-
Albumin
-
Potassium
-
Bicarbonate
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.
Anemia workup
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 is less than 12 g/dL or the hematocrit is less than 37%.
Glomerular Filtration Rate
All patients with an abnormal creatinine clearance should have their GFR estimated. Several eGFR formulas that employ easily obtainable values have been developed (eg, Modification of Diet in Renal Disease (MDRD) formula, Cockcroft-Gault formula). The National Kidney Foundation (NKF) recommends using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation to estimate GFR. [27]
Staging
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 (further subdivided as Stage 3A with GFR 45-59, and Stage 3B with GFR 30-44 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
Ultrasonography
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 blood urea nitrogen (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.
Biopsy
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.
Histology
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.
