Alpha-1-Microglobulin, 24 Hour, Urine
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Alpha-1-microglobulin is a low-molecular-weight protein of 26 kDa and a member of the lipocalin protein superfamily.(1) It is synthesized in the liver, freely filtered by glomeruli, and reabsorbed by renal proximal tubules cells where it is catabolized.(1) Due to extensive tubular reabsorption, under normal conditions very little filtered alpha-1-microglobulin appears in the final excreted urine. Therefore, an increase in the urinary concentration of alpha-1-microglobulin indicates proximal tubule injury and/or impaired proximal tubular function.
Elevated excretion rates can indicate tubular damage associated with renal tubulointerstitial nephritis or tubular toxicity from heavy metal or nephrotoxic drug exposure. Glomerulonephropathies and renal vasculopathies also are often associated with coexisting tubular injury and so may result in elevated excretion. Elevated alpha-1-microglobulin in patients with urinary tract infections may indicate renal involvement (pyelonephritis).
Measurement of urinary excretion of retinol-binding protein, another low-molecular-weight protein, is an alternative to the measurement of alpha-1-microglobulin. To date, there are no convincing studies to indicate that one test has better clinical utility than the other.
Urinary excretion of alpha-1-microglobulin can be determined from either a 24-hour collection or from a random urine collection. The 24-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 variabilities in urine concentration.
Assessment of renal tubular injury or dysfunction
Screening for tubular abnormalities
Detecting chronic asymptomatic renal tubular dysfunction(2)
Alpha-1-microglobulin above the reference values may be indicative of a proximal tubular dysfunction.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Since this is a nephelometric assay, turbidity and particles (eg, cells, crystals) in the specimen can interfere with the test.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
> or =16 years: <19 mg/24 hours
7 mg/g creatinine is a literature suggested upper reference limit for pediatrics 1 month to 15 years of age.*
*Hjorth L, Helin I, Grubb A: Age-related reference limits for protein HC in children. Scand J Clin Lab Invest 2000 Feb;60(1):65-73
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Akerstrom B, Logdberg L, Berggard T, et al: Alpha-1-microglobulin: a yellow-brown lipocalin. Biochim Biophys Acta 2000 Oct 18;1482(1-2):172-184
2. Yu H, Yanagisawa Y, Forbes M, et al: Alpha-1-microglobulin: an indicator protein for renal tubular function. J Clin Pathol 1983 Mar;36(3):253-259
3. Hjorth L, Helin I, Grubb A: Age-related reference limits for urine levels of albumin, orosomucoid, immunoglobulin G, and protein HC in children. Scand J Clin Lab Invest 2000 Feb;60(1):65-73