Alpha-1-Microglobulin, Random, Urine

CPT CODE:

USEFUL FOR:

Assessment of renal tubular injury or dysfunction
Screening for tubular abnormalities
Detecting chronic asymptomatic renal tubular dysfunction

SPECIMEN REQUIRED:

5 mL from a random urine collection. No preservative. Sendspecimen refrigerated in a plastic, 13-mL urine tube.

TRANSPORT TEMPERATURE:

Refrig\Ambient OK\Frozen OK

CLINICAL INFORMATION:

Alpha-1-microglobulin is a low-molecular-weight protein of 26 kDaand a member of the lipocalin protein superfamily.(1) It issynthesized in the liver, freely filtered by glomeruli, andreabsorbed by renal proximal tubules cells where it is catabolized.(1) Due to extensive tubular reabsorption, undernormal conditions very little filtered alpha-1-microglobulin appearsin the final excreted urine. Therefore, an increase in the urinaryconcentration of alpha-1-microglobulin indicates proximal tubuleinjury and/or impaired proximal tubular function.
Elevated excretion rates can indicate tubular damage associatedwith renal tubulointerstitial nephritis or tubular toxicity from heavymetal or nephrotoxic drug exposure. Glomerulonephropathies andrenal vasculopathies also are often associated with coexistingtubular injury and so may result in elevated urinary alpha-1-micro-globulin excretion. Elevated alpha-1-microglobulin in patients withurinary tract infections may indicate renal involvement (pyelo-nephritis). Measurement of urinary excretion of retinol-bindingprotein, another low-molecular-weight protein, is an alternative tothe measurement of alpha-1-microglobulin. To date, there are noconvincing studies to indicate that 1 test has better clinical utility than the other.
Urinary excretion of alpha-1-microglobulin can be determined fromeither a 24-hour collection or from a random urine collection. The24-hour collection is traditionally considered the gold standard.For random or spot collections, the concentration of alpha-1-microglobulin is divided by the urinary creatinine concentration. This corrected value adjusts alpha-1-microglobulin for variabilitiesin urine concentration.

CLINICAL INTERPRETATION:

Alpha-1-microglobulin above the reference values may indicate a proximal tubular dysfunction. As suggested in the literature, 7 mg/g creatinine is an upper reference limit for pediatric patients of 1 month to 15 years of age

REFERENCE VALUES:

<50 years:  <13 mg/g creatinine

> or =50 years:  <20 mg/g creatinine