Urine Beta-2 Microglobulin Unit Converter
Urine Beta-2 Microglobulin Unit Converter
Urine beta-2 microglobulin is a proximal tubular marker, not the myeloma stage marker the serum test is. Convert µg/L, ng/mL, mg/L and nmol/L.
Urine Beta-2 Microglobulin converter
Mass ⇄ molarUrine beta-2 microglobulin 300 µg/L, the upper reference limit
Formula and conversion factor
µg/L = nmol/L ÷ 0.0852588
mg/L = µg/L ÷ 1,000
ng/mL = µg/L (the same quantity)
- 0.0852588
- derived from a molecular weight of 11,729 Da for the mature protein. The serum page prints 85.26 for mg/L to nmol/L; this is the same number a thousand times smaller, because urine beta-2 microglobulin is reported in micrograms per litre
- µg/L and ng/mL
- numerically identical — no arithmetic is needed between them
- µg/g creatinine
- a different quantity again: the ratio to creatinine, which corrects for how dilute the specimen is. ARUP’s limit happens to be 300 in both
Worked example
Urine beta-2 microglobulin 300 µg/L, the upper reference limit
300 × 0.0852588 = 25.58 nmol/L
= 300 ng/mL = 0.300 mg/L
At the upper limit both ARUP and Mayo publish for a random urine
Check the specimen pH before acting on a raised value: beta-2 microglobulin is degraded in acid urine, so a low result in an acidic sample may be an artefact
Urine beta-2 microglobulin: reference limits
| Source | Limit | Unit |
|---|---|---|
| ARUP, urine beta-2 microglobulin | 0 – 300 | µg/L |
| The same limit in SI | 0 – 25.58 | nmol/L |
| ARUP, ratio to creatinine | 0 – 300 | µg/g creatinine |
| Mayo B2MU, random urine | ≤ 300 | µg/L |
| The same limit expressed in mg/L | ≤ 0.300 | mg/L |
| Serum beta-2 microglobulin, adult | 0.8 – 2.4 | mg/L |
What a raised value means depends on which side it comes from
| Pattern | Serum beta-2 microglobulin | Urine beta-2 microglobulin |
|---|---|---|
| Proximal tubular injury | Normal | Raised — the filtered protein is not reabsorbed |
| Cadmium, mercury or other heavy-metal exposure | Normal | Raised; this is the classic occupational monitoring use |
| Aminoglycoside, cisplatin or tenofovir toxicity | Normal | Raised, often early |
| Myeloma, lymphoma, HIV, inflammation | Raised | May be raised from the filtered load alone, with intact tubules |
| Reduced glomerular filtration | Raised | Variable |
A tubular marker that borrows a tumour marker’s name
Beta-2 microglobulin is the invariant light chain of the class I major histocompatibility complex, an 11.7 kDa protein shed from the surface of every nucleated cell. At that size it passes the glomerular filter almost freely and is then reabsorbed and catabolised in the proximal tubule, so in health almost none reaches the final urine. That arrangement is what makes it useful twice over, for two unrelated questions.
In serum it is a marker of cell turnover and of glomerular filtration, which is why it carries prognostic weight in myeloma and lymphoma and appears in the ISS myeloma staging calculator. In urine it is a marker of proximal tubular function: if the tubule is injured it stops reclaiming the filtered protein and the urine concentration rises, often before the creatinine moves. That is the basis of its use in monitoring cadmium and mercury exposure, in aminoglycoside, cisplatin and tenofovir nephrotoxicity, and in distinguishing tubular from glomerular proteinuria. The serum beta-2 microglobulin converter is a different test with a different interval and a different question; so is the alpha-1 microglobulin converter, the other low-molecular-weight tubular marker, which has the practical advantage of being stable in acid urine.
Two traps. The first is overflow: a sufficiently high serum concentration raises the filtered load enough to produce a raised urine result with entirely normal tubules, so a urine beta-2 microglobulin cannot be read without a serum one. Myeloma, lymphoma, HIV and any brisk inflammatory state all do this. The second is pre-analytical and is the reason many laboratories prefer alpha-1 microglobulin: beta-2 microglobulin is degraded by lysosomal proteases in acid urine, losing much of its immunoreactivity below about pH 6, so a falsely low result in a concentrated acidic morning sample is entirely possible. Alkalinising the specimen or collecting it fresh is part of the method, not an afterthought.
The units are simple but easy to misread. Urine beta-2 microglobulin is reported in µg/L, which is numerically identical to ng/mL, and the molar equivalent is nmol/L at 0.0852588 per µg/L. Serum beta-2 microglobulin is reported in mg/L, a thousand times larger, and the serum page’s factor of 85.26 is this one multiplied by a thousand. Results are also issued as a ratio to creatinine in µg/g, a third quantity that needs the urine creatinine on the same specimen.
Frequently asked questions
How do I convert urine beta-2 microglobulin from µg/L to nmol/L?
Multiply by 0.0852588, derived from the protein’s molecular weight of 11,729 Da. So 300 µg/L is 25.58 nmol/L. µg/L and ng/mL are the same number, and mg/L is the µg/L figure divided by a thousand.
Is urine beta-2 microglobulin the same test as the serum one?
No. The serum test measures cell turnover and glomerular filtration and is a prognostic marker in myeloma and lymphoma. The urine test measures proximal tubular reabsorption. The reference intervals differ by a factor of about a thousand and the clinical questions are unrelated.
What raises urine beta-2 microglobulin?
Proximal tubular injury — heavy metals, aminoglycosides, cisplatin, tenofovir, interstitial nephritis, Fanconi syndrome. But also a high serum concentration, which raises the filtered load enough to overwhelm normal tubular reabsorption, so myeloma, lymphoma, HIV and inflammation can raise the urine value with healthy tubules. A serum level is needed to tell the two apart.
Why does the laboratory ask about the urine pH?
Because beta-2 microglobulin is degraded in acid urine and loses immunoreactivity below about pH 6, so an acidic specimen can give a falsely low result. Some laboratories alkalinise the collection; others prefer alpha-1 microglobulin or retinol-binding protein, which are stable at low pH.
Should the result be reported per litre or per gram of creatinine?
Per gram of creatinine if the specimen is a random one, because that corrects for how dilute the urine is. ARUP’s upper limit happens to be 300 in both µg/L and µg/g creatinine, which is a coincidence of the numbers rather than a statement that the two are interchangeable.
Related calculators
References
- ARUP Laboratories. Beta-2 microglobulin, urine — reference interval and ratio to creatinine. Laboratory Test Directory 0080432; 2026.
- Mayo Clinic Laboratories. Beta-2 microglobulin, random, urine (B2MU) — reference values. Test catalogue, test ID 602026; 2026.
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int. 2024;105(4S):S117–S314.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/