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Test ID A1M24 Alpha-1-Microglobulin, 24 Hour, Urine

Reporting Name

Alpha-1-Microglobulin, 24-Hour, U

Useful For

Assessment of renal tubular injury or dysfunction

 

Screening for tubular abnormalities

 

Detecting chronic asymptomatic renal tubular dysfunction(2)

Specimen Type

Urine


Specimen 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

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 day

Method Name

Immunonephelometry

Urine Preservative Collection Options

Ambient

Yes

Refrigerated

Preferred

Frozen

Yes

6N HCI

No

50% Acetic Acid

Yes

Na2CO3

No

Toluene

Yes

6N HNO3

No

Boric Acid

Yes

Thymol

Yes