Plasma copper measures the concentration of copper in plasma (the liquid portion of blood without cells). It primarily reflects caeruloplasmin-bound copper, as approximately 60-95% of plasma copper is carried by caeruloplasmin, the main copper transport protein produced by the liver. A small fraction is free copper or loosely bound to albumin.
Plasma copper is elevated in inflammatory conditions (as caeruloplasmin is an acute phase reactant), in oestrogen excess (pregnancy, oral contraceptive use), and in copper toxicity. It is reduced in copper deficiency and in Wilson's disease (where paradoxically free plasma copper is markedly elevated while caeruloplasmin-bound copper may be low). Plasma copper is interpreted alongside caeruloplasmin and urine copper for complete copper status assessment.
FAQs
Is plasma copper different from serum copper?
Plasma copper and serum copper are very similar. Plasma is from blood collected into anticoagulant tubes; serum is from clotted blood. Both primarily reflect caeruloplasmin-bound copper. In practice, the terms are often used interchangeably though plasma is the technically preferred specimen.
Can excess zinc cause low copper?
Yes. Zinc and copper compete for intestinal absorption via the same transport mechanisms. High zinc intake (from supplements) induces metallothionein in intestinal cells, which preferentially binds copper and prevents its absorption. Long-term high-dose zinc supplementation can cause copper deficiency.
Why can plasma copper be low in Wilson's disease?
Wilson's disease is caused by impaired copper excretion into bile, leading to copper accumulation. Despite high total body copper, caeruloplasmin (which carries most plasma copper) is reduced in Wilson's disease. Free (non-caeruloplasmin-bound) copper is elevated, but total plasma copper may appear normal or low. Urine copper and liver copper biopsy are more reliable for Wilson's diagnosis.
What foods are highest in copper?
Shellfish (particularly oysters), organ meats (liver, kidneys), dark chocolate, nuts, seeds, legumes, and whole grains are the richest dietary sources of copper.
