Zinc to Copper Ratio Calculator
Zinc to Copper Ratio Calculator
Calculate the serum zinc to copper ratio, and see why it is an orientation aid rather than a validated cut-off — and why inflammation makes it unreliable.
Zinc to Copper Ratio
Zn ÷ CuSerum zinc 90 µg/dL, serum copper 105 µg/dL
Formula
Both values must be in the same unit
- same unit
- µg/dL ÷ µg/dL or µmol/L ÷ µmol/L; mixing the two produces a nonsensical result
- mass vs molar
- zinc (65.38) and copper (63.55) have slightly different atomic weights, so a molar ratio differs from a mass ratio by about 3%
- CRP
- copper rises and zinc falls with inflammation, so the ratio moves in acute illness without any change in nutritional status
Worked example
Serum zinc 90 µg/dL, serum copper 105 µg/dL
90 ÷ 105 = 0.86
Within the range implied by typical adult reference intervals
Both concentrations are individually within their usual intervals, which is what the ratio should always be read against
Typical adult serum reference intervals
| µg/dL | µmol/L | Multiply µg/dL by | |
|---|---|---|---|
| Zinc | 70 – 120 | 10.7 – 18.4 | 0.153 |
| Copper | 70 – 140 | 11.0 – 22.0 | 0.157 |
Reading the ratio — orientation only
| Ratio | Pattern | Consider |
|---|---|---|
| < 0.6 | Low | Zinc deficiency; copper excess including Wilson disease; acute inflammation, which lowers zinc and raises copper |
| 0.6 – 1.2 | Typical | Consistent with usual reference intervals; does not exclude a problem with either metal |
| > 1.2 | Raised | Copper deficiency — high-dose zinc supplementation, bariatric surgery, long-term parenteral nutrition, malabsorption |
A ratio with no validated cut-off, and how to use it anyway
Be clear at the outset: there is no consensus reference interval for the serum zinc to copper ratio. The bands used here are derived arithmetically from typical adult reference intervals — zinc roughly 70–120 µg/dL and copper roughly 70–140 µg/dL — and are offered as orientation, not as a validated diagnostic threshold. The ratio should always be read alongside both absolute concentrations, because a ratio of 0.9 is compatible with two normal results and equally with two markedly abnormal ones that happen to move together.
Both values must be entered in the same unit. If µmol/L is used, the ratio is not quite the same number as the mass ratio: zinc has an atomic weight of 65.38 and copper 63.55, so converting both to molar units shifts the ratio by about 3%. That is small relative to the analytical and biological variation of either measurement, but it means a molar ratio and a mass ratio should not be compared against the same figure without acknowledging the offset — and mixing the units outright produces a meaningless result.
The physiology that makes the ratio interesting is competitive absorption. Zinc induces enterocyte metallothionein, which binds copper with higher affinity than zinc and holds it in the cell until it is shed, so sustained high-dose zinc intake causes copper deficiency. This is a real and repeatedly described clinical problem, presenting with a sideroblastic-type anaemia and neutropenia that can mimic myelodysplasia on marrow examination, and sometimes with a myelopathy resembling subacute combined degeneration. Zinc-containing denture adhesives, self-prescribed zinc, bariatric surgery and long-term parenteral nutrition are the usual settings.
The ratio’s main weakness is inflammation. Caeruloplasmin is a positive acute-phase reactant, so copper rises with any inflammatory illness and with oestrogen use and pregnancy, while zinc falls as it redistributes into the liver. Both changes push the ratio down together, and a low ratio in an acutely unwell patient is more likely to reflect the illness than nutritional status. Measure a CRP alongside, and repeat when the patient is well. A genuinely low ratio raises the question of zinc deficiency or copper excess, including Wilson disease, but neither diagnosis is made on the ratio: Wilson disease needs caeruloplasmin, 24-hour urinary copper, slit-lamp examination and often genetic testing.
Frequently asked questions
What is a normal zinc to copper ratio?
There is no consensus reference interval. The bands shown here, roughly 0.6 to 1.2, are derived from typical adult reference intervals for the two metals and are orientation only. Always interpret alongside both absolute concentrations.
Does it matter whether I use µg/dL or µmol/L?
Both values must be in the same unit. Because zinc (65.38) and copper (63.55) have slightly different atomic weights, a molar ratio differs from a mass ratio by about 3%, so the same figure should not be applied to both without allowing for that.
Can zinc supplements cause copper deficiency?
Yes. Zinc induces enterocyte metallothionein, which traps copper in the intestinal cell. Sustained high-dose zinc causes copper deficiency, presenting with a sideroblastic-type anaemia and neutropenia that can mimic myelodysplasia, and sometimes a myelopathy.
Why is the ratio unreliable in acute illness?
Copper is an acute-phase reactant and rises with inflammation, oestrogen use and pregnancy, while zinc falls as it redistributes to the liver. Both changes lower the ratio at once, so it should be interpreted with a CRP and repeated once the patient is well.
Can a low ratio diagnose Wilson disease?
No. A low ratio may prompt the question, but Wilson disease is diagnosed on caeruloplasmin, 24-hour urinary copper excretion, slit-lamp examination for Kayser-Fleischer rings, and often ATP7B genetic testing.
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References
- Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academies Press; 2001.
- Willis MS, Monaghan SA, Miller ML, et al. Zinc-induced copper deficiency: a report of three cases initially recognized on bone marrow examination. Am J Clin Pathol. 2005;123(1):125–131.
- 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.