Test (specimen or method) |
Units |
Purpose |
Benefits |
Limitations |
Urinalysis (dipstick) |
Varies with component subtest |
Screening test for a variety of systemic diseases, renal diseases, and disorders of the urinary tract
Morphometric and biochemical analysis of urine components |
Widely available
Measures specific gravity, pH, protein, glucose, ketones, bilirubin, occult blood, leukocyte esterase, nitrite, urobilinogen, WBCs, RBCs, casts, and bacteremia
Assesses presence of crystals |
Result may be altered by contaminated reagent strips, reading a strip at the wrong time, exercise
Specimen volume <2 mL may limit the number of subtests that can be performed |
Microalbuminuria (24-h urine, timed overnight 10-h urine collection, spot AM urine after initial voiding) |
mg/L or mg/24 h
Spot collections:
μg albumin/
mg creatinine |
Detects small amounts of albumin
Result predicts development of proteinuria (progression of diabetic nephropathy)
Result strongly supports a diagnosis of diabetic nephropathy |
Creatinine clearance may be measured from the same urine specimen
Measures lower concentrations of albumin than can be detected by dipstick methods |
Usually sent to a reference laboratory
UAE may decline 30% to 50% at night
Result may be altered by exercise, pregnancy, fever, inflammatory disorders, urinary tract infection, urinary tract bleeding, or benign postural proteinuria
|
Proteinuria, quantitative (24-h urine) |
mg/24 h |
Follow-up assessment of proteinuria and diabetic nephropathy |
Readily available |
Vigilant oversight of specimen collection
Check with laboratory regarding need for refrigeration or preservative
Result may be altered by intrinsic variation in proteinuria, x-ray contrast media,* tolbutamine, antibiotics |
Creatinine (serum or plasma) |
mg/dL |
Result can be used to calculate approximate GFR |
Readily available; most commonly ordered test of renal function |
Moderate changes in GFR may not be detected
Relatively insensitive indicator for GFR, especially in early renal failure
Result may be altered by meat ingestion, pregnancy, muscular disorders, hyperthyroidism, cephalosporin antibiotics, corticosteroids, cimetidine, other drugs |
Creatinine clearance (urine) |
mL/min/m2 |
Estimates GFR |
Readily available; second most commonly ordered test of renal function
Can use 24-h urine specimen or 2 consecutive 2-h urine specimens |
Must order with blood creatinine
Body surface area needed to calculate
Relatively insensitive indicator for GFR, especially in early renal failure
Result may be altered by exercise, ketone bodies, glucose, pregnancy, cephalosporins, cimetidine, other drugs |
Creatinine (12- or 24-h urine) |
Children: mg/kg/24 h
Adults: g/24h |
Only useful as a renal function test when performed as part of creatinine clearance |
Readily available |
Must order with blood creatinine
Creatinine reabsorption may occur in uncontrolled diabetes, very low urine flow rates
Vigilant oversight of specimen collection and refrigeration
Result may be altered by meat ingestion, pregnancy, cimetidine, other drugs |
Cystatin C (serum or plasma) |
mg/L |
Estimates GFR
Assesses allograft function |
Muscle mass independence
Diet independence
Age, height, & gender independent in children |
Higher cost than creatinine tests
Not readily available |
