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HelpTest Code RA1U Alpha-1-Microglobulin, Random, Urine
Specimen Required
Container/Tube: Plastic, 5-mL tube
Specimen Volume: 5 mL
Collection Instructions:
1. Collect a random urine specimen.
2. No preservative.
Useful For
Assessment of renal tubular injury or dysfunction using random urine specimens
Screening for tubular abnormalities
Detecting chronic asymptomatic renal tubular dysfunction (2)
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| AIMR | Alpha-1-Microglobulin, Random, U | No | Yes |
| CRETR | Creatinine, Random, U | Yes, (Order RCTUR) | Yes |
Method Name
AIMR: Immunonephelometry
CRETR: Enzymatic Colorimetric Assay
Reporting Name
Alpha-1-Microglobulin, Random, USpecimen Type
UrineSpecimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Urine | Refrigerated (preferred) | 7 days | |
| Frozen | 7 days |
Reject Due To
| All specimens will be evaluated at Mayo Clinic Laboratories for test suitability. |
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 urinary alpha-1-microglobulin 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.
Reference Values
≥18 years: <35 mg/g creatinine
Reference values have not been established for patients who are less than 18 years of age.
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.(3)
Cautions
Since this is a nephelometric assay, turbidity and particles (eg, cells, crystals) in the sample can interfere with the test. Therefore, all urine specimens should be centrifuged at ambient temperature prior to assay.
Method Description
Alpha-1-Microglobulin:
In an immunochemical reaction, alpha-1-microglobulin present in the urine sample forms immune complexes with anti-alpha-1-microglobulin-specific antibodies. These complexes scatter a beam of light passed through the sample. The intensity of the scattered light is proportional to the concentration of alpha-1-microglobulin in the sample. The result is evaluated by comparison with a standard of known concentration.(Package insert: N Alpha-1-microglobulin. Siemens; V5, 05/2018)
Creatinine:
Creatinine is performed by the enzymatic method, which is based on the determination of sarcosine from creatinine with the aid of creatininase, creatinase, and sarcosine oxidase. The liberated hydrogen peroxide is measured via a modified Trinder reaction using a colorimetric indicator. Optimization of the buffer system and the colorimetric indicator enables the creatinine concentration to be quantified both precisely and specifically.(Package insert: Creatinine plus ver 2. Roche Diagnostics; V15.0, 03/2019)
Day(s) Performed
Varies
Report Available
1 to 7 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| RA1U | Alpha-1-Microglobulin, Random, U | 48415-4 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| A1M_U | Alpha-1-Microglobulin, Random, U | 46723-3 |
| CRETR | Creatinine, Random, U | 2161-8 |
| A1M_R | A1M/Creat Ratio | 48415-4 |