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HelpTest ID A1M24 Alpha-1-Microglobulin, 24 Hour, Urine
Reporting Name
Alpha-1-Microglobulin, 24-Hour, UUseful For
Assessment of renal tubular injury or dysfunction
Screening for tubular abnormalities
Detecting chronic asymptomatic renal tubular dysfunction(2)
Specimen Type
UrineSpecimen Required
Container/Tube: Plastic, 5-mL tube
Specimen Volume: 4 mL
Collection Instructions:
1. Collect urine for 24 hours.
2. No preservative.
3. Mix well before taking 4-mL aliquot.
Additional Information:
1. 24-Hour volume is required.
2. See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens in Special Instructions for multiple collections.
Specimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Urine | Refrigerated (preferred) | 7 days |
| Ambient | 7 days | |
| Frozen | 7 days |
Special Instructions
Reference Values
≥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
Day(s) and Time(s) Performed
Varies; 8 a.m. to 4 p.m.
Test Classification
This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.CPT Code Information
83883
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| A1M24 | Alpha-1-Microglobulin, 24-Hour, U | 48414-7 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| AIM | Alpha-1-Microglobulin, 24-Hour, U | 48414-7 |
| A1MCR | A1M/Creat Ratio | 48415-4 |
| DUR5 | Collection Duration | 13362-9 |
| VL58 | Urine Volume | 3167-4 |
| A1MC | Alpha-1-Microglobulin Concentration | In Process |
| CR_C | Creatinine Concentration | 20624-3 |
Clinical Information
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.
Interpretation
Alpha-1-microglobulin above the reference values may be indicative of a proximal tubular dysfunction.
Clinical Reference
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
Analytic Time
1 dayMethod Name
Immunonephelometry