Blood Chromium Unit Converter

Convert whole blood chromium between µg/L, ng/mL, nmol/L and µmol/L. Most people having this test have a metal-on-metal hip, and the MHRA action level of 7 ppb is nothing like an occupational exposure limit.

Last updated 8 Oct 2026

Blood Chromium converter

Mass ⇄ molar

Whole blood chromium

EDTA whole blood, in a metal-free tube. Chromium is 100 to 1,000 times more concentrated in the environment than in tissue, so contamination reads high.

Reference figureThe first two are reference intervals for people without an implant. The MHRA figure is a device-surveillance action level and is seven times either of them; it is not a toxicity threshold.

134.6nmol/LExample

Whole blood chromium 7 µg/L, the MHRA action level

The conversion, and the regulator’s own arithmetic

nmol/L = µg/L × 19.2322
µg/L = nmol/L × 0.0519961
µmol/L = µg/L × 0.0192322 · ppb = µg/L

19.2322: from chromium’s atomic weight, 51.9961 (CIAAW 2024). MDA/2017/018 prints 7 ppb as 134.5 nmol/L; this factor gives 134.63, so the alert’s figure is rounded by 0.09% and not derived from a different mass
ppb: parts per billion. In whole blood this is µg/L, so the MHRA’s 7 ppb and a report of 7 µg/L are the same number — a point the alert leaves implicit
total chromium: what the assay measures. It does not distinguish trivalent from hexavalent chromium, which is why the occupational index is written as a within-shift increase rather than a single concentration

Worked example

Whole blood chromium 7 µg/L, the MHRA action level
7 × 19.2322 = 134.6 nmol/L
MDA/2017/018 prints this level as "7ppb (134.5 nmol/L chromium)" — the 0.1 nmol/L difference is the alert rounding, not a disagreement about chromium's atomic weight
Seven times Mayo's upper reference limit of 1.0 µg/L for an adult without an implant, and in Labcorp's moderate-risk band for one with

Chromium figures, and what kind of figure each one is

Four different kinds of number, and only the top two are reference intervals. The MHRA action level is seven times Mayo’s upper limit and triggers imaging, not treatment. The ACGIH indices are urinary and for a workforce, cited here by value rather than reproduced as a table. Reference intervals are method- and laboratory-dependent, and the interval printed on your own report takes precedence over any figure here.
Source	µg/L (ppb)	nmol/L	Kind of figure
Mayo CRWB, adults	< 1.0	< 19.2	Reference interval, no implant
Exeter, whole blood	0 – 5.20	0 – 100	Reference interval
Labcorp 738770	< 3.0	< 57.7	Low-risk band, implant
Labcorp 738770	3.0 – 10.0	57.7 – 192.3	Moderate-risk band
Labcorp 738770	> 10.0	> 192.3	High-risk band
MHRA MDA/2017/018	≥ 7	≥ 134.5	Device-surveillance action level
ACGIH BEI, hexavalent Cr in urine	+10.0 within shift; 24.9 end of week	—	Occupational exposure index

The pre-analytical trap, which is larger than the arithmetic

Mayo warns that without metal-free collection a raised result "may be an incidental and misleading finding". Where the action level is seven times the reference limit, a contaminated specimen can manufacture an indication for imaging.
Problem	What it does
Environmental chromium	100 to 1,000 times higher than in tissue (Mayo)
Wrong tube	Needs royal blue EDTA, metal-free; Mayo forbids opening it beforehand
Serum instead of whole blood	Not interchangeable; MHRA and FDA both specify whole blood
Aliquoting	Mayo: send the original tube, do not aliquot

Why the reader is probably holding an arthroplasty result

Whole blood chromium in µg/L becomes nmol/L on multiplication by 19.2322, from chromium’s atomic weight of 51.9961. Parts per billion in whole blood is µg/L, so the regulator’s 7 ppb and a laboratory’s 7 µg/L are the same thing. The conversion can be checked against the MHRA’s own figures: MDA/2017/018 prints 7 ppb as 134.5 nmol/L, and this factor gives 134.63 — a 0.09% difference that is the alert rounding and nothing more.

Occupational chromium exposure still exists, in plating, welding and tanning, but it is not why most of these tests are requested. The common indication is surveillance of a metal-on-metal hip or a cobalt-chromium knee, and it has its own numbers. The MHRA sets an action level of 7 ppb for either metal, at which the alert asks for closer follow-up and cross-sectional imaging; Labcorp bands results as low risk under 3.0 ng/mL, moderate from 3.0 to 10.0 and high above 10.0. None of these is a toxicity threshold, and both Mayo and Labcorp say so in unusually direct terms: Mayo that raised trace element concentrations "in the absence of corroborating clinical information do not independently predict prosthesis wear or failure", Labcorp that "metal ion levels alone should not be relied on as the sole parameter to determine clinical recommendations for revision surgery".

The specimen rules are strict and the reason is quantitative. Mayo states that chromium is present in the environment at 100-fold to 1000-fold higher concentration than in biological tissues, so almost any contamination swamps the measurement. The requirement is EDTA whole blood in a royal blue metal-free tube, sent in the original tube and not aliquoted, and the MHRA adds that the analysis should be done by a laboratory in the Trace Elements External Quality Assessment Scheme. Whole blood, serum and plasma are not interchangeable.

One more disagreement. The 2010 MHRA guidance was quoted as 135 nmol/L for chromium and 120 for cobalt; the 2017 version gives 134.5 and 119. Both describe the same 7 ppb, rounded differently. Chromium is read alongside blood cobalt, the pair the alert is written about.

Frequently asked questions

How do I convert blood chromium from µg/L to nmol/L?

Multiply by 19.2322, from chromium’s atomic weight of 51.9961. A whole blood chromium of 7 µg/L is 134.6 nmol/L, which is the MHRA’s 7 ppb action level — the alert itself prints 134.5.

Is 7 ppb the same as 7 µg/L?

In whole blood, yes. One part per billion by mass is one microgram per litre to within the density of blood, which is why the MHRA’s 7 ppb and a laboratory’s 7 µg/L are used interchangeably in arthroplasty follow-up.

What is the MHRA chromium action level for a metal-on-metal hip?

MDA/2017/018 gives whole blood metal levels at or above 7 ppb — 134.5 nmol/L for chromium, 119 nmol/L for cobalt — as indicating the need for closer follow-up and cross-sectional imaging. It is a surveillance trigger, not a level at which chromium is toxic.

Can a raised blood chromium be contamination?

Readily. Mayo notes chromium is 100 to 1,000 times more concentrated in the environment than in tissue, and warns that without metal-free collection a raised result may be an incidental and misleading finding. Royal blue EDTA, original tube, not aliquoted.

Does a high chromium mean the hip needs revising?

No. Labcorp states that metal ion levels alone should not be the sole parameter determining a recommendation for revision surgery, and Mayo that they do not independently predict prosthesis wear or failure. The level sits alongside symptoms, function scores and imaging.

Related calculators

References

Mayo Clinic Laboratories. Chromium, blood (CRWB). Test catalogue, test ID 65601; 2026. "≥18 years: <1.0 ng/mL"; "Chromium is present in the environment at 100-fold to 1000-fold higher concentration than found in biological tissues"; "Increased blood trace element concentrations in the absence of corroborating clinical information do not independently predict prosthesis wear or failure".
Labcorp. Chromium and cobalt, whole blood — test 738770. Test menu; 2026. Low risk <3.0 ng/mL, moderate 3.0–10.0, high >10.0, each analyte separately; "metal ion levels alone should not be relied on as the sole parameter to determine clinical recommendations for revision surgery".
Medicines and Healthcare products Regulatory Agency. Medical Device Alert MDA/2017/018: all metal-on-metal (MoM) hip replacements — updated advice for follow-up of patients. Issued 29 June 2017. "Whole blood metal levels ≥7ppb (119 nmol/L cobalt or 134.5 nmol/L chromium)" indicates "the need for closer follow-up and cross-sectional imaging".
Exeter Clinical Laboratory International. Chromium and cobalt — metal ion monitoring. Test handbook; accessed October 2026. Chromium "0–100 nmol/L", cobalt "0–20 nmol/L"; quotes MDA/2010/033 as "above 120 nmol/L (cobalt) or 135 nmol/L (chromium)", and a referral threshold of "a cobalt level > 340 nmol/L, with or without symptoms".
Mayo Clinic Laboratories. Chromium occupational exposure, random, urine (CRUO). Test catalogue, test ID 65719; 2026. The ACGIH biological exposure index for hexavalent chromium in urine is "an increase of 10.0 mcg/L between pre-shift and post-shift urine collections" and "an end-of-shift concentration above 24.9 mcg/L at the end of the work week".
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/