Blood Arsenic Unit Converter
Blood Arsenic Unit Converter
Convert whole blood arsenic between µg/L, ng/mL, µg/dL, nmol/L and µmol/L. Blood arsenic has a half-life of hours and goes undetectable about two days after exposure, which is why urine is the test an occupational physician orders.
Blood Arsenic converter
Mass ⇄ molarWhole blood arsenic reported as 13 µg/L, the upper limit Mayo prints
The conversion, and the atomic weight behind it
µg/L = nmol/L × 0.0749216
µmol/L = µg/L × 0.0133473 · µg/dL = µg/L ÷ 10
- 13.3473
- derived from arsenic’s standard atomic weight, 74.921595 (CIAAW 2024) — an element has an exact mass, so unlike a metabolite there is nothing to argue about here
- ng/mL = µg/L
- the same quantity written twice; Mayo prints ng/mL and ARUP prints µg/L, and no arithmetic is needed between them
- 4–6 hours
- the blood half-life of inorganic arsenic; the methylated metabolites run 20 to 30 hours, and after about two days neither is detectable
Worked example
Whole blood arsenic reported as 13 µg/L, the upper limit Mayo prints
13 × 13.3473 = 173.5 nmol/L
= 13 ng/mL = 1.300 µg/dL = 0.1735 µmol/L
At Mayo's limit, just above ARUP's 12.0 µg/L, and nearly twice the upper limit the SAS laboratory publishes (95 nmol/L, which is 7.12 µg/L on this mass)
What the laboratories publish for blood arsenic
| Source | Interval | As printed |
|---|---|---|
| Mayo ASB, all ages | 0 – 13 µg/L | < 13 ng/mL |
| ARUP 0099045, adults | 0 – 12.0 µg/L | ≤ 12.0 µg/L |
| SAS, whole blood | 1.05 – 7.12 µg/L | 14 – 95 nmol/L |
| SAS, serum or plasma | 1.50 – 7.49 µg/L | 20 – 100 nmol/L |
Blood and urine arsenic answer different questions
| Whole blood arsenic | Urine arsenic | |
|---|---|---|
| Window | The last 1 – 2 days | The last several days to a week |
| Half-life | 4 – 6 h inorganic; 20 – 30 h metabolites | Renal clearance over days |
| Main use | Acute or very large exposure | The standard exposure test |
| Seafood effect | Modest | Large — total arsenic can rise several-fold |
| What to order | ARUP: recent poisoning only | Speciated, not total |
Why a normal blood arsenic proves almost nothing
Whole blood arsenic in µg/L becomes nmol/L on multiplication by 13.3473, a factor that follows directly from arsenic’s standard atomic weight of 74.921595. ng/mL and µg/L are identical, and µg/dL is µg/L divided by ten. Because arsenic is an element, the factor is not open to dispute in the way a metabolite’s is — there is no acid-versus-anion choice to make.
What is open to dispute is what a result means. Mayo gives the blood half-life of inorganic arsenic as 4 to 6 hours and of its methylated metabolites as 20 to 30 hours, and states that arsenic "is not likely to be detected in blood specimens drawn more than 2 days after exposure". A blood arsenic is therefore a test for acute poisoning, and a normal one in a patient asking about last month’s well water or last year’s smelter job carries no information at all. Both Mayo and ARUP say the same thing in their ordering guidance: urine is the specimen for assessing exposure.
The intervals disagree more than the chemistry does. Mayo publishes under 13 ng/mL, ARUP 12.0 µg/L or less — close enough — while the UK Supraregional Assay Service publishes 14 to 95 nmol/L for whole blood, whose upper limit is 7.12 µg/L on arsenic’s mass. A result of 10 µg/L is normal at both US laboratories and clearly raised at the UK one, and nothing about the patient has changed. Part of the difference is dietary: a population that eats more fish carries more non-toxic organic arsenic, and a total-arsenic assay counts it.
Which is the point that matters most when the result is followed up. The confirmatory test is a urine arsenic, and it must be the speciated one. Urine arsenic explains why a total result is confounded by arsenobetaine from seafood. For the other metals read on the same panel, see blood lead, blood cadmium and blood mercury, each of which has its own specimen rule.
Frequently asked questions
How do I convert blood arsenic from µg/L to nmol/L?
Multiply by 13.3473, which comes from arsenic’s atomic weight of 74.921595. A blood arsenic of 13 µg/L is 173.5 nmol/L. To go back, multiply nmol/L by 0.0749216.
Is ng/mL the same as µg/L for arsenic?
Yes, exactly. One nanogram per millilitre is one microgram per litre, so Mayo’s "less than 13 ng/mL" and a report of "13 µg/L" mean the same thing. µg/dL, which is the unit blood lead is reported in, is µg/L divided by ten.
Does a normal blood arsenic rule out arsenic poisoning?
Only very recent poisoning. Mayo states arsenic is unlikely to be detected in blood more than two days after exposure, because the inorganic form has a half-life of 4 to 6 hours. For anything other than an acute presentation, a urine arsenic is the test.
Why do the laboratories give such different upper limits?
Mayo gives under 13 ng/mL and ARUP 12.0 µg/L or less, but the UK SAS laboratory gives 14 to 95 nmol/L for whole blood, an upper limit of 7.12 µg/L. Diet is part of it: a total-arsenic assay counts the non-toxic organic arsenic that comes from fish. Read your result against your own laboratory’s interval.
Should I order blood or urine arsenic?
Blood for an acute presentation inside about 48 hours. Urine, speciated, for everything else, including occupational surveillance and chronic environmental exposure. ARUP’s ordering note says blood arsenic is for recent exposure poisoning only.
Related calculators
References
- Mayo Clinic Laboratories. Arsenic, blood (ASB) — reference values. Test catalogue, test ID 8645; 2026. <13 ng/mL, all ages; "The half-life of inorganic arsenic in blood is 4 to 6 hours, and the half-life of the methylated metabolites is 20 to 30 hours"; "Urine is the preferred specimen for assessment of arsenic exposure".
- ARUP Laboratories. Arsenic, blood. Laboratory Test Directory 0099045; 2026. "Less than or equal to 12.0 µg/L"; "Blood arsenic is for the detection of recent exposure poisoning only"; avoid "shellfish and seafood for 48 to 72 hours".
- Supraregional Assay Service, Trace Element laboratory. Arsenic. sas-centre.org; accessed October 2026. Whole blood 14–95 nmol/L, serum or plasma 20–100 nmol/L; "Diets rich in seafood give misleading results (several thousand nmol/L have been reported) due to presence of non-toxic organo-arsenic compounds"; urine arsenobetaine median 51.6 nmol/L, 95th centile 1690 nmol/L.
- Agency for Toxic Substances and Disease Registry. Toxicological Profile for Arsenic. Atlanta, GA: US Department of Health and Human Services.
- Commission on Isotopic Abundances and Atomic Weights, IUPAC. Standard Atomic Weights 2024. ciaaw.org; accessed October 2026. As 74.921595(6), Mn 54.938043(2), Al 26.9815384(3), Cr 51.9961(6), Co 58.933194(3), Tl [204.382, 204.385]; for the interval elements the IUPAC abridged values Tl 204.38, C 12.011, N 14.007 are used.
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/