Beta-2 Microglobulin Unit Converter

Q: How do I convert beta-2 microglobulin from mg/L to nmol/L?

Multiply by 85.26, a factor derived from its molecular mass of 11,729 Da. A level of 1.9 mg/L is 162 nmol/L. µg/mL is numerically identical to mg/L.

Q: Why does renal impairment raise beta-2 microglobulin?

The protein is small enough to be filtered freely at the glomerulus and is then reabsorbed and catabolised in the proximal tubule, so clearance depends almost entirely on glomerular filtration. As filtration falls, serum levels rise steeply, and this dominates any other interpretation.

Q: How is beta-2 microglobulin used in myeloma?

It is one of the two variables of the International Staging System, alongside serum albumin. Stage I requires a level below 3.5 mg/L with albumin at or above 3.5 g/dL, and stage III a level at or above 5.5 mg/L. The Revised ISS adds LDH and cytogenetics.

Q: What does a raised urine beta-2 microglobulin mean?

It indicates proximal tubular dysfunction rather than glomerular disease, because the filtered protein is normally almost completely reabsorbed there. It is used to detect tubular injury from cadmium and other heavy metals, tenofovir and tubulointerstitial disease.

Q: Does the urine sample need special handling?

Yes. Beta-2 microglobulin degrades rapidly at a urinary pH below about 5.5, so samples are alkalinised before or at collection. Without that step the result reads falsely low.

Convert beta-2 microglobulin between mg/L, µg/mL and nmol/L, with the ISS myeloma thresholds and why renal function dominates the interpretation.

Last updated 3 Sep 2026

Beta-2 Microglobulin converter

Mass ⇄ molar

Beta-2 microglobulin

Divide nmol/L by 85.26 to get mg/L. µg/mL is numerically identical to mg/L.

Reference groupThis interval assumes normal renal function. Serum levels rise steeply with any fall in glomerular filtration.

162nmol/LExample

Beta-2 microglobulin 1.9 mg/L

Formula and conversion factor

nmol/L = mg/L × 85.26
mg/L = nmol/L ÷ 85.26
µg/mL = mg/L (numerically identical)

85.26: derived from the molecular mass of beta-2 microglobulin, 11,729 Da
µg/mL: numerically identical to mg/L; no conversion is needed between them
renal handling: at 11.7 kDa it is filtered freely and then reabsorbed and catabolised in the proximal tubule, so serum levels track glomerular filtration
ISS: International Staging System for myeloma — stage I below 3.5 mg/L with albumin at or above 3.5 g/dL, stage III at or above 5.5 mg/L

Worked example

Beta-2 microglobulin 1.9 mg/L
1.9 × 85.26 = 162 nmol/L
= 1.90 µg/mL
Within the adult reference interval of 0.8–2.4 mg/L

Reference interval and staging thresholds in both units

µg/mL is numerically identical to mg/L. The nmol/L column is the mg/L figure multiplied by 85.26.
	mg/L	nmol/L
Adult reference interval, normal renal function	0.8 – 2.4	68 – 205
ISS stage I threshold	< 3.5	< 298
ISS stage III threshold	≥ 5.5	≥ 469

International Staging System for myeloma

The Revised ISS adds serum LDH and high-risk cytogenetics to these two variables.
Stage	Beta-2 microglobulin	Albumin
I	< 3.5 mg/L	≥ 3.5 g/dL
II	Neither stage I nor stage III	—
III	≥ 5.5 mg/L	Any

Why renal function comes first

Beta-2 microglobulin is the invariant light chain of the MHC class I molecule, present on the surface of every nucleated cell and shed continuously into plasma. It is reported in mg/L, which is numerically identical to µg/mL, and less often in nmol/L; the factor of 85.26 between them derives from its molecular mass of 11,729 daltons. The molecule’s small size is the key to everything else about it.

At 11.7 kDa it passes freely through the glomerulus and is then almost entirely reabsorbed and catabolised in the proximal tubule, so that under one per cent of the filtered load appears in urine. Serum levels therefore track glomerular filtration closely and rise steeply as it falls. In practice this dominates interpretation: in a patient with renal impairment, a raised serum beta-2 microglobulin says far more about the kidneys than about anything else, and no other explanation should be pursued until renal function has been accounted for.

Its main clinical use is in myeloma, where it is one of the two variables of the International Staging System alongside serum albumin, and carries forward into the Revised ISS. That prognostic value reflects both tumour burden and renal function, which is part of why it works, since renal impairment is itself an adverse feature in myeloma. It also rises in lymphoma and chronic lymphocytic leukaemia, in chronic viral infection including HIV, and in inflammatory disease, none of which is specific.

Urine beta-2 microglobulin is a different test with a different meaning. Because the filtered load is normally reabsorbed almost completely, a raised urinary level indicates proximal tubular dysfunction rather than glomerular leak, and it is used to detect tubular injury from cadmium and other heavy metals, from tenofovir, and from tubulointerstitial disease. Urine samples need alkalinisation, because the protein degrades rapidly below a urinary pH of about 5.5 and a falsely low result follows.

Frequently asked questions

How do I convert beta-2 microglobulin from mg/L to nmol/L?

Multiply by 85.26, a factor derived from its molecular mass of 11,729 Da. A level of 1.9 mg/L is 162 nmol/L. µg/mL is numerically identical to mg/L.

Why does renal impairment raise beta-2 microglobulin?

The protein is small enough to be filtered freely at the glomerulus and is then reabsorbed and catabolised in the proximal tubule, so clearance depends almost entirely on glomerular filtration. As filtration falls, serum levels rise steeply, and this dominates any other interpretation.

How is beta-2 microglobulin used in myeloma?

It is one of the two variables of the International Staging System, alongside serum albumin. Stage I requires a level below 3.5 mg/L with albumin at or above 3.5 g/dL, and stage III a level at or above 5.5 mg/L. The Revised ISS adds LDH and cytogenetics.

What does a raised urine beta-2 microglobulin mean?

It indicates proximal tubular dysfunction rather than glomerular disease, because the filtered protein is normally almost completely reabsorbed there. It is used to detect tubular injury from cadmium and other heavy metals, tenofovir and tubulointerstitial disease.

Does the urine sample need special handling?

Yes. Beta-2 microglobulin degrades rapidly at a urinary pH below about 5.5, so samples are alkalinised before or at collection. Without that step the result reads falsely low.

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References

Greipp PR, San Miguel J, Durie BGM, et al. International staging system for multiple myeloma. J Clin Oncol. 2005;23(15):3412–3420.
Palumbo A, Avet-Loiseau H, Oliva S, et al. Revised International Staging System for multiple myeloma: a report from International Myeloma Working Group. J Clin Oncol. 2015;33(26):2863–2869.

Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.