Zinc Unit Converter
Zinc Unit Converter
Convert plasma or serum zinc between µg/dL, µmol/L, µg/L and mg/L. The harder question is what the converted number is worth: the cut-off changes with sex, age, the time of day and whether the patient had eaten, the result falls in any inflammatory state, and a rubber stopper or a haemolysed sample destroys the measurement outright.
Zinc converter
µg/dL ⇄ µmol/LPlasma zinc 90 µg/dL, morning fasting sample from an adult man, CRP normal
The ladder, and the one constant in it
µg/dL = µmol/L × 6.5381
because 1 µg/dL is 1 × 10⁻⁵ g/L, and 10⁻⁵ ÷ 65.38 g/mol = 1.5295 × 10⁻⁷ mol/L
- 0.15295
- ten divided by zinc’s standard atomic weight of 65.38. Zinc is an element, so unlike a protein or a glycoprotein the molar mass is not an assumption and the conversion is exact
- 6.5381
- the reciprocal. IZiNCG’s technical brief prints "divide by 6.54" beside its cut-off table and Gibson’s textbook prints "multiply by 6.536"; both are roundings of this number and the difference is well under a tenth of a µmol/L at any clinical concentration
- µg/L and mg/L
- µg/dL × 10 gives µg/L, and µg/dL ÷ 100 gives mg/L. Trace-element laboratories using inductively coupled plasma mass spectrometry often report in µg/L for consistency across the whole panel, so the same patient’s zinc can appear as 90 µg/dL or 900 µg/L
- what no factor fixes
- the specimen. A haemolysed sample, a non-trace-element tube or a rubber stopper adds zinc that no arithmetic can remove, and an afternoon or post-prandial draw moves the number without moving the patient’s zinc status
Worked example
Plasma zinc 90 µg/dL, morning fasting sample from an adult man, CRP normal
90 × 0.15295 = 13.8 µmol/L
90 × 10 = 900 µg/L, and 90 ÷ 100 = 0.900 mg/L
Above the 74 µg/dL morning-fasting cut-off for males 10 years and over, and inside the quoted laboratory interval
The normal CRP matters as much as the number: a low result with a raised CRP would have been uninterpretable, because inflammation shifts zinc into the liver
Had this been an afternoon sample the cut-off would have been 61 µg/dL rather than 74 — a change of 13 µg/dL from the clock alone
If the patient is taking zinc, the number to check next is the copper: see the zinc to copper ratio calculator
IZiNCG’s suggested lower cut-offs, and the molar column derived from them
| Group | Morning, fasting | Morning, not fasting | Afternoon |
|---|---|---|---|
| Males 10 years and over | 74 µg/dL = 11.3 µmol/L | 70 µg/dL = 10.7 µmol/L | 61 µg/dL = 9.3 µmol/L |
| Females 10 years and over, not pregnant | 70 µg/dL = 10.7 µmol/L | 66 µg/dL = 10.1 µmol/L | 59 µg/dL = 9.0 µmol/L |
| Children under 10 years | not available | 65 µg/dL = 9.9 µmol/L | 57 µg/dL = 8.7 µmol/L |
| Spread from the clock alone | — | — | 13 µg/dL in males, 11 in females |
Four reasons a plasma zinc may not mean what it says
| Problem | What the sources say | What to do about it |
|---|---|---|
| Inflammation | "Acute and chronic infection and systemic inflammation leads to serum or plasma zinc values that are spuriously low because of the transfer of zinc from the blood to the liver". IZiNCG: "Because plasma zinc concentration is reduced in the presence of inflammation, it is recommended to include the analyses of acute-phase proteins" — CRP for acute, AGP for chronic | Measure a CRP converter alongside. Whether to numerically ADJUST the zinc is contested — see the caption |
| Time of day and fasting | Afternoon samples run about 9% lower than morning ones independent of fasting status, which is why IZiNCG publishes a separate cut-off for each combination | Standardise the draw to morning fasting where possible; where it cannot be, read against the matching cut-off above rather than a single interval |
| Haemolysis | Erythrocyte zinc greatly exceeds plasma zinc; a reported effect is about a 5% rise in plasma or serum zinc per gram of haemoglobin per litre. IZiNCG: "Discard any obviously hemolyzed samples" | Reject and redraw. A visibly haemolysed zinc is not a result with a caveat, it is a different measurement |
| The tube | "Collect into trace element-free evacuated blood collection tubes", with "stoppers, and serum separators" that "should be pre-screened for zinc prior to use"; siliconised rather than rubber stoppers. One laboratory’s instructions add that the specimen "must always be drawn first", not from a line, and "do not ream the specimen with a wooden stick" | Use the royal-blue-top trace-element tube and draw it first. Zinc from a rubber stopper or a wooden applicator is indistinguishable in the result from zinc from the patient |
Why the plasma concentration is a poor status marker even when everything goes right
| Fact | Consequence |
|---|---|
| "Only 0.1% of the total body zinc is present in the serum", against 63% in skeletal muscle and 3% in the liver | The compartment being sampled is a rounding error on the pool being assessed, and it is homeostatically defended |
| Plasma zinc is maintained across mild and moderate depletion | A normal plasma zinc does not exclude deficiency. This is the single most common misreading of the test |
| It responds to inflammation, stress, the time of day and the last meal | Several of the things that move it have nothing to do with zinc intake or stores |
| It does fall in severe depletion, and it does respond to repletion | It is not useless. It is a population-level indicator and a confirmatory test in severe deficiency, rather than a screening test for marginal status |
| No functional biomarker has displaced it | Which is why it is still ordered. The honest framing is that this is the best available marker of a thing it measures badly |
An exact conversion on an inexact measurement
The arithmetic is as clean as it gets on this site. Zinc is an element, so its molar mass is not an assumption about glycosylation or a calibrator convention: the standard atomic weight is 65.38, a microgram per decilitre is 10⁻⁵ g/L, and dividing gives 1.5295 × 10⁻⁷ mol/L. So µg/dL × 0.15295 = µmol/L and the reciprocal is 6.5381, which is the "divide by 6.54" that IZiNCG prints beside its own table. Micrograms per litre is the µg/dL figure times ten and milligrams per litre is that figure divided by a hundred, which matters because a trace-element laboratory running the whole panel by mass spectrometry will often report 900 µg/L where a chemistry analyser reports 90 µg/dL.
Everything difficult about this test is upstream of that. Start with the cut-off, because there is not one. IZiNCG publishes eight, because the expected concentration depends on sex, on age, on the time of day and on whether the patient had eaten: 74 µg/dL for a fasting adult male in the morning, 61 µg/dL for the same man in the afternoon. That is a 13 µg/dL swing produced by the clock, comparable to the difference a clinician would want to act on, and it is why a zinc result without a collection time is weaker evidence than it looks. Afternoon samples run around nine per cent below morning ones irrespective of fasting.
Then the inflammation problem, which is the one to remember. Cytokines drive hepatic metallothionein synthesis and zinc moves out of the plasma into the liver, so an unwell patient’s plasma zinc falls without their zinc stores changing at all. IZiNCG’s recommendation follows directly: measure an acute-phase protein alongside — CRP for acute inflammation, α-1-acid glycoprotein for chronic — and treat an elevated one as a reason not to read the zinc. Whether the zinc should then be numerically adjusted is genuinely contested. The BRINDA project pooled twelve surveys and found the relation inconsistent: deficiency prevalence rose across CRP deciles in half the preschool-child surveys, the association in women of reproductive age was weak and inconsistent, and the authors concluded that there is insufficient evidence to warrant inflammation adjustment in that group. The defensible position for a single patient is therefore narrower than a correction factor: measure the CRP, and if it is up, the zinc has not answered your question.
Then the specimen, where this analyte is unusually unforgiving in both directions. Erythrocytes carry far more zinc than plasma does, so haemolysis raises the result — about five per cent per gram of haemoglobin per litre has been reported — and a visibly haemolysed sample should be redrawn rather than reported with a comment. Contamination raises it too, and the sources of contamination are the ordinary furniture of a blood draw: rubber stoppers, non-trace-element tubes, serum separators, talc, a wooden applicator stick. Hence the instructions that come with the test — a trace-element tube with a siliconised stopper, pre-screened for zinc, drawn first rather than from a line, transferred into a metal-free polypropylene vial. Zinc that entered the sample from a stopper is indistinguishable, in the number, from zinc that came from the patient.
And finally the limitation that survives doing all of that correctly. Only about a tenth of a per cent of body zinc is in the serum, against roughly sixty per cent in skeletal muscle, and the plasma concentration is homeostatically defended across mild and moderate depletion. A normal plasma zinc therefore does not exclude zinc deficiency, which is the commonest misreading of this test. It falls reliably in severe depletion and it rises on repletion, so it is a reasonable confirmatory test and a reasonable population indicator; it is a poor screening test for marginal status, and where the clinical picture suggests deficiency the response to replacement is more informative than the concentration.
One thing a genuinely high plasma zinc should always prompt, once contamination and haemolysis are excluded: check the copper. Zinc supplementation induces intestinal metallothionein and causes copper deficiency, which presents as anaemia, neutropenia or a myelopathy and is regularly missed. The zinc to copper ratio calculator puts the two together, and the caeruloplasmin converter covers the protein that carries most of the circulating copper. For the other trace elements on the same panel, see the blood lead converter and the vitamin B12 converter.
Frequently asked questions
How do I convert zinc from µg/dL to µmol/L?
Multiply by 0.15295, or divide by 6.54 to go the other way. The factor is ten divided by zinc’s standard atomic weight of 65.38, and because zinc is an element the conversion is exact rather than a convention. So a zinc of 90 µg/dL is 13.8 µmol/L. Micrograms per litre is the µg/dL figure multiplied by ten, and milligrams per litre is it divided by a hundred.
What is a normal plasma zinc?
There is no single figure, and the reason is clinically useful rather than pedantic. IZiNCG publishes a different lower cut-off for each combination of sex, age, time of day and fasting state: 74 µg/dL for a fasting adult male in the morning, 70 for the same man not fasting, 61 in the afternoon, and 70, 66 and 59 for adult females. Reference laboratories publish their own intervals — one gives 60 to 106 µg/dL for adults — which can disagree with the IZiNCG figure by more than 10 µg/dL. Read against the interval printed on your own report and note which combination it assumes.
Does a normal plasma zinc rule out zinc deficiency?
No, and this is the most important limitation of the test. Only about 0.1% of body zinc is in the serum, against roughly 63% in skeletal muscle, and the plasma concentration is homeostatically defended through mild and moderate depletion. Plasma zinc falls reliably in severe deficiency and responds to repletion, which makes it a useful confirmatory and population-level measure, but it is a poor screening test for marginal status. Where the clinical picture suggests deficiency, the response to a trial of replacement is more informative than the concentration.
Why should a CRP be measured with a plasma zinc?
Because inflammation lowers plasma zinc without changing zinc stores. Cytokines drive hepatic metallothionein synthesis and zinc moves from the circulation into the liver, so acute or chronic inflammation produces a spuriously low result. IZiNCG recommends measuring acute-phase proteins alongside — CRP for acute and α-1-acid glycoprotein for chronic inflammation. Whether to numerically adjust the zinc is contested: the BRINDA project found the association inconsistent across twelve surveys and concluded there is insufficient evidence to warrant adjustment in women of reproductive age. Treat a low zinc with a raised CRP as uninterpretable rather than as a number to correct.
Does haemolysis affect a zinc result?
Yes, upwards, and enough to matter. Erythrocytes contain far more zinc than plasma, so lysis releases it into the sample; a rise of roughly 5% per gram of haemoglobin per litre has been reported. IZiNCG’s own protocol says to discard obviously haemolysed samples. A visibly haemolysed zinc should be redrawn, not reported with a caveat, because there is no way to tell from the number how much of it came from the red cells.
Why does zinc need a special tube?
Because zinc is everywhere in the collection kit. Rubber stoppers, ordinary evacuated tubes, serum separators, talc and wooden applicator sticks all carry enough zinc to raise a result measurably, and plasma zinc is a low concentration by comparison. The published instructions call for trace-element-free tubes with siliconised stoppers, pre-screened for zinc, transferred after centrifugation into a metal-free polypropylene vial; one laboratory adds that the specimen must always be drawn first and never from a line. Contaminating zinc is indistinguishable, in the result, from the patient’s own.
My zinc is high. Does that matter?
First exclude contamination and haemolysis, which are commoner causes of a high plasma zinc than zinc excess. If the result stands and the patient is taking a zinc supplement, the important consequence is not the zinc but the copper: zinc induces intestinal metallothionein, which binds copper and blocks its absorption, and zinc-induced copper deficiency presents as anaemia, neutropenia or a myelopathy that is regularly attributed to something else. Check a serum copper and caeruloplasmin.
Related calculators
References
- International Zinc Nutrition Consultative Group. Assessing population zinc status with serum zinc concentration. IZiNCG Technical Brief No. 2, 2nd ed., 2012. Table 1 lower cut-offs in µg/dL — morning fasting 74 (males ≥10y) and 70 (females ≥10y); morning non-fasting 70, 66 and 65 (children <10y); afternoon 61, 59 and 57 — with "For conversion to μmol/L, divide by 6.54"; "Fasting is defined as no food or beverage consumption for at least 8 hours"; "Collect into trace element-free evacuated blood collection tubes"; "Discard any obviously hemolyzed samples".
- International Zinc Nutrition Consultative Group. Practical Tips. "Because plasma zinc concentration is reduced in the presence of inflammation, it is recommended to include the analyses of acute-phase proteins", namely "C-reactive protein (CRP) (biomarker of acute inflammation) and a-1 acid glycoprotein (AGP) (biomarker of chronic inflammation)".
- Gibson RS, et al. Principles of Nutritional Assessment, 3rd ed., chapter on zinc. "Acute and chronic infection and systemic inflammation leads to serum or plasma zinc values that are spuriously low because of the transfer of zinc from the blood to the liver"; "Only 0.1% of the total body zinc is present in the serum", with 63% in skeletal muscle and 3% in liver; afternoon samples about 9% lower than morning; about "a 5% increase in plasma or serum zinc concentration … with each 1g hemoglobin/L"; siliconised rather than rubber stoppers.
- Adjusting plasma or serum zinc concentrations for inflammation: Biomarkers Reflecting Inflammation and Nutritional Determinants of Anemia (BRINDA) project. Am J Clin Nutr. 2023. "In 6 of 12 PSC surveys, the estimated prevalence of zinc deficiency increased with increasing CRP deciles"; "In WRA, the association of PZC with CRP and AGP was weak and inconsistent"; "Relations between PZC and inflammatory markers were inconsistent, suggesting that correlation and decile analyses should be conducted before applying any inflation adjustments"; "At this time, there is insufficient evidence to warrant inflammation adjustment in WRA".
- Mayo Clinic Laboratories. Zinc, Serum, test ZN_S. Reference values "0-10 years: 60-120 mcg/dL, 11-17 years: 66-110 mcg/dL, ≥18 years: 60-106 mcg/dL"; "6-mL Plain, royal blue-top Vacutainer plastic trace element blood collection tube"; "This specimen must always be drawn first"; "Do not collect specimen from a line"; "do not ream the specimen with a wooden stick"; "Avoid hemolysis".
- Duncan A, Yacoubian C, Watson N, Morrison I. The risk of copper deficiency in patients prescribed zinc supplements. J Clin Pathol. 2015;68(9):723–725.
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.