BETA-2-MICROGLOBULIN (SERUM)

Code
900.0700
Name
BETA-2-MICROGLOBULIN (SERUM)
Category
None
Department
Send-Out
Start Date
Expiration Date
Synonyms
B2M
CPT Codes
82232
Site
SBMF
Reference Test
30008
ATLAS Test Code

BETA2

Specimen Information

Type

Gold, SST

Volume

1.0 ml

Transport Info

Refrigerated

Fasting Required?
False
Patient Instructions

Reference Range

Less than or equal to 2700 µg/L

Methodology

Chemiluminescence Immunoassay (CLIA)

Clinical Significance

Measurements of B2M are considered a sensitive means for diagnosing proximal tubular dysfunction and is reportedly the most reliable test for distinguishing upper from lower urinary tract infections, and a useful method for assessing the results of therapy and diagnosing recurrences of acute pyelonephritis using serial determinations. B2-Microglobulin (B2M) was first isolated in 1968 from the urine of patients with Wilson's disease and cadmium poisoning. It has since been identified as the light chain of the HLA-A, -B, -C major histocompatibility complex antigens, 100 amino acids in length and noncovalently associated with the heavy chain. In structure and amino acid sequence, it resembles the CH3 region of IgG, though it is antigenically distinct. B2M occurs on the surface of nucleated cells -- abundantly on lymphocytes and monocytes -- and on many tumor cell lines. Its function is unknown, but it may control the expression and biosynthesis of antigens on the cell surface. Because of its low molecular weight, 95% of all free B2M is rapidly eliminated by glomerular filtration. Proximal tubular cells then take up 99.9% of this filtered amount by endocytosis, after which degradation to amino acids occurs. Normal urinary excretion of B2M is less than 370 micrograms per 24 hours; higher rates are interpreted as evidence of tubular dysfunction. Increased urinary excretion of B2M has been observed in a wide variety of conditions including Wilson's disease, Fanconi's syndrome, untreated congenital galactosemia, nephrocalcinosis, cystinosis, chronic potassium depletion, interstitial nephritis, connective-tissue disease such as rheumatoid arthritis and Sjogern's syndrome, occupational exposure to heavy metals such as cadmium and mercury, upper urinary tract infections, kidney transplantation, and nephrotoxicity resulting from cyclosporin, aminoglycoside or cisplatinum therapy. Elevated serum concentrations in the presence of a normal glomerular filtration rate suggest increased B2M production or release. Increased levels may be seen in lymphoproliferative diseases.

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