Alpha-1-Microglobulin Unit Converter
Alpha-1-Microglobulin Unit Converter
Convert alpha-1-microglobulin between mg/L, µg/mL, µg/L and mg/dL. A1M is a proximal tubular marker, not a glomerular one, and this page is explicit about the one arm it does not offer: the mg/g creatinine ratio, which needs a urine creatinine no converter has.
Alpha-1-microglobulin converter
Mass unitsUrine alpha-1-microglobulin 8.0 mg/L
Formula and conversion factors
µg/L = mg/L × 1000
mg/dL = mg/L ÷ 10
mg/g creatinine = A1M (mg/L) ÷ urine creatinine (g/L) — not computable here
- mg/L and µg/mL
- the same quantity written two ways. One milligram in a litre is one microgram in a millilitre; there is no factor and nothing to get wrong except assuming there is one
- no molar unit
- A1M is reported as a mass and this page offers no nmol/L. The free monomer is about 26 kDa, but roughly half of the plasma protein circulates as a reduction-resistant one-to-one complex with monomeric IgA, 7% bound to albumin and 1% to prothrombin, so there is no single molecular mass for the measurand
- mg/g creatinine
- the unit most laboratories actually report, and the one this converter cannot produce. It requires the urine creatinine from the same sample, which is a second measurement, not a constant. Divide the A1M in mg/L by the urine creatinine in g/L; if your creatinine is in mg/dL, divide it by 100 first
- why the ratio exists at all
- a spot urine concentration is a statement about hydration as much as about the tubule. The same tubular leak reads 4 mg/L in a dilute sample and 40 mg/L in a concentrated one, which is why no defensible adult reference interval in mg/L exists and why this record carries no reference range
Worked example
Urine alpha-1-microglobulin 8.0 mg/L
8.0 mg/L = 8.00 µg/mL — the same number
= 8,000 µg/L = 0.800 mg/dL
To reach the reported unit you need the creatinine: at a urine creatinine of 0.8 g/L, 8.0 ÷ 0.8 = 10 mg/g creatinine
Below Mayo's adult threshold of 35 mg/g creatinine — but only because a creatinine was supplied. The 8.0 mg/L on its own supports no verdict at all
Published thresholds, and the unit each belongs to
| Sample | Threshold | Source |
|---|---|---|
| Random urine, 18 years and over | < 35 mg/g creatinine | Mayo Clinic Laboratories, test RA1U, immunonephelometry |
| Random urine, 1 month to 15 years | Upper reference limit 7 mg/g creatinine | Mayo Clinic Laboratories, test RA1U |
| 24-hour urine, 18 years and over | < 23 mg/24 hours | Mayo Clinic Laboratories, test A124 |
| Random urine, concentration alone | No defensible threshold | None — a mg/L figure is uninterpretable without a creatinine or a timed collection |
Tubular against glomerular: two different leaks
| Alpha-1-microglobulin | Albumin | |
|---|---|---|
| Size | About 26 kDa free, mostly complexed with IgA in plasma | 66 kDa |
| Normal handling | Filtered freely, then reabsorbed by megalin on the proximal tubule and catabolised | Almost entirely retained by the glomerular filter |
| A raised urine level means | The proximal tubule has stopped reabsorbing what the glomerulus normally lets through | The glomerular filter is leaking something it should hold back |
| Typical causes | Cadmium and other heavy metals, tenofovir, aminoglycosides, cisplatin, tubulointerstitial nephritis, pyelonephritis, Fanconi syndrome | Diabetic kidney disease, hypertension, glomerulonephritis |
| What it is not | A measure of filtration rate, and not interchangeable with albuminuria | A tubular marker |
A protein the tubule is supposed to take back
Alpha-1-microglobulin — protein HC in the older literature — is a small yellow-brown lipocalin, one of the three original members of that family alongside retinol-binding protein and beta-lactoglobulin. The free monomer is about 26 kDa, small enough to pass the glomerular filter almost unhindered. In healthy kidneys nearly all of what is filtered is then bound by megalin on the proximal tubular brush border, taken into the cell and catabolised, so very little reaches the bladder. A raised urinary A1M therefore does not say the filter is leaking. It says the tubule has stopped collecting.
That is a different statement from albuminuria and it is worth keeping the two apart deliberately. Albumin at 66 kDa is held back by the glomerulus, so albumin in urine means the filter has failed — the signature of diabetic kidney disease, hypertensive nephropathy and glomerulonephritis. A1M in urine means the tubule has failed, which is the signature of cadmium and other heavy metals, of tenofovir, aminoglycosides and cisplatin, of tubulointerstitial nephritis, of pyelonephritis with renal involvement, and of Fanconi syndrome. A patient can have a perfectly normal albumin-creatinine ratio and a markedly raised A1M. Substituting one test for the other misses exactly the disease the other was ordered to find.
A1M is measured rather than beta-2 microglobulin largely for a pre-analytical reason, and it is usually overstated. Donaldson and colleagues measured all three low-molecular-weight proteins across 135 urine samples and found beta-2 microglobulin unstable below pH 7 and grossly so below pH 6 — but they also found A1M and retinol-binding protein significantly lower in the non-alkalinised fractions at pH below 7, and recommended measuring the pH and alkalinising at the time of voiding for all three. A1M is more robust than beta-2 microglobulin. It is not indifferent to an acid urine.
This page converts the numerator and no more. mg/L and µg/mL are the same number, µg/L is a thousand times larger and mg/dL a tenth as large, and all of those are exact. The unit laboratories actually report — milligrams per gram of creatinine — is not on the list, because producing it needs the urine creatinine from the same specimen and there is no fixed factor standing in for it. For the same reason the record carries no reference interval: a concentration in mg/L is a statement about how much the patient drank as much as about the tubule, and quoting a range for it would be inventing one. Mayo’s thresholds are in the table above, in the units they belong to, with the division spelled out so you can do it once you have the creatinine.
Serum A1M is a different test again, with a different meaning: it rises as glomerular filtration falls, in the same way beta-2 microglobulin and cystatin C do, and it is not a tubular marker in that compartment. Check which sample your report refers to before interpreting anything.
Frequently asked questions
Is mg/L the same as µg/mL for alpha-1-microglobulin?
Yes, exactly. One milligram per litre is one microgram per millilitre. No arithmetic is required and no factor exists; laboratories simply choose one label or the other.
How do I convert alpha-1-microglobulin to mg/g creatinine?
Divide the A1M in mg/L by the urine creatinine in g/L from the same sample. If the creatinine is reported in mg/dL, divide it by 100 first to get g/L. This page cannot do it for you because the creatinine is a second measurement, not a constant, and no converter has it.
What is a normal urine alpha-1-microglobulin?
Only expressed against creatinine or against time. Mayo Clinic Laboratories gives under 35 mg/g creatinine on a random urine for adults, an upper reference limit of 7 mg/g creatinine from one month to fifteen years, and under 23 mg per 24 hours on a timed collection. There is no useful reference interval for a spot concentration in mg/L, which is why this page does not print one.
How is alpha-1-microglobulin different from albuminuria?
They report on opposite parts of the nephron. Albumin is normally held back by the glomerulus, so albumin in urine means the filter is leaking. A1M is normally filtered and then reabsorbed by the proximal tubule, so A1M in urine means the tubule has stopped reabsorbing. A patient can have one without the other.
Why is A1M preferred to beta-2 microglobulin?
Mainly stability. Beta-2 microglobulin degrades in urine below pH 7 and grossly so below pH 6, which produces falsely low results. A1M holds up better — but in the same study it too read lower in non-alkalinised acid urine, so the advice to check the pH and alkalinise at voiding applies to both.
Why does this page offer no molar unit?
Because there is no single molecular mass to convert against. The free protein is about 26 kDa, but roughly half of plasma A1M circulates as a reduction-resistant one-to-one complex with monomeric IgA, with smaller fractions bound to albumin and prothrombin. A1M is reported as a mass concentration and nothing is lost by leaving it that way.
Related calculators
References
- Mayo Clinic Laboratories. Alpha-1-Microglobulin, Random, Urine (RA1U), test 610364: <35 mg/g creatinine for ages 18 and over, by immunonephelometry.
- Mayo Clinic Laboratories. Alpha-1-Microglobulin, 24 Hour, Urine (A124), test 610363: <23 mg/24 hours for ages 18 and over.
- Donaldson MDC, Chambers RE, Woolridge MW, Whicher JT. Stability of alpha1-microglobulin, beta2-microglobulin and retinol binding protein in urine. Clin Chim Acta. 1989;179(1):73–77.
- Åkerström B, Lögdberg L, Berggård T, Osmark P, Lindqvist A. alpha-1-Microglobulin: a yellow-brown lipocalin. Biochim Biophys Acta. 2000;1482(1–2):172–184.
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.