At least 8 million Americans are affected by kidney disease. Kidney failure kills more people per year than colon cancer, breast cancer, or prostate cancer combined. Chronic kidney disease or kidney failure raises a patient’s risk of cardiovascular disease dramatically.
To support a diagnosis of renal disease or dysfunction, a number of laboratory assays may be performed.
Renal Function Panel
|ASSAY||TYPE OF SPECIMEN|
|Albumin||Serum or plasma|
|Calcium||Serum or plasma|
|Carbon dioxide||Serum or plasma|
|Creatinine||Serum or plasma|
|Chloride||Serum or plasma|
|Glucose||Serum or plasma|
|Phosphorous, inorganic||Serum or plasma|
|Potassium||Serum or plasma|
|Sodium||Serum or plasma|
|Urea nitrogen||Serum or plasma|
Additional renal function markers may be useful.
Renal Function Markers
|TEST NAME||TYPE OF SPECIMEN||RECOMMENDED USE|
|Alpha-1 (α1 -) microglobulin||Urine||May indicate renal involvement in patients with urinary tract infections or diabetes mellitus|
|Beta-2 (β2-) microglobulin||Urine||May indicate renal involvement in patients with diabetic nephropathy, cadmium toxicity, or progressing idiopathic membranous nephropathy|
|Glomerular filtration rate, estimated||Calculation||Monitor renal function. (Test reports serum creatinine reference intervals.)|
|Alpha-2 (α2 -) macroglobulin||Urine||May be used as a marker of membrane permeability in serum and fluids; may be used as a screening test|
|Microalbumin||Urine||Useful in monitoring diabetic nephropathy in insulin-dependent diabetes mellitus|
|Cystatin C||Serum||May be a marker of renal disease; however, test lacks specificity.|
Nitrogen (N) occurs in the body in a variety of ways, the majority of which are components of complex substances. Nitrogen-containing substances are divided into two categories: protein nitrogen (nitrogen-containing protein substances) and non-protein nitrogen (NPN). Urea is the most abundant NPN constituent, accounting for more than 75% of total NPN excretion; other NPNs, in order of quantitative significance, are amino acids, uric acid, creatinine, creatine, and ammonia.
More than 90% of urea is normally excreted by the kidneys. As a result of reduced renal activity, urea nitrogen, uric acid, and creatinine levels rise. Increased concentrations of some of NPN’s major constituents are used to diagnose impaired renal function. When tests for renal function are needed, most laboratories conduct serum urea nitrogen measurements in conjunction with creatinine tests, since combined assays are more specific indicators of renal function disorders. Because of the unpredictable blood levels caused by non-renal causes, the serum urea nitrogen test alone is limited in its ability to assess kidney function. A urea nitrogen/creatinine ratio is commonly calculated:
A typical ratio for a person on a normal diet is between 12 and 20. Significantly lower ratios suggest acute tubular necrosis, insufficient protein intake, malnutrition, or extreme liver disease. High ratios of normal creatinine values suggest tissue breakdown, prerenal azotemia, or a high protein intake. High ratios with increased creatinine can suggest a postrenal obstruction or prerenal azotemia associated with a renal disease.