Urinary zinc excretion in patients with different disorders: the acute phase response in the kidney

While depressed circulating zinc levels constitute a well-characterized part of the acute phase response, relatively little attention has been paid to the changes in urinary zinc excretion, although urine zinc output has been reported to be elevated in various disorders, mainly those known to be accompanied by inflammatory phenomena. In order to assess the significance of urinary zinc loss and its relationship with the acute phase response, zinc concentration was determined by atomic absorption spectrophotometry together with creatinine in urine samples of patients with different disorders. Plasma zinc, C-reactive protein, alpha-1 acid glycoprotein, haptoglobin, prealbumin, transferrin, and iron have also been determined in some patients. In accordance with the results of previous studies, we report an increase in urinary zinc, notably in solid tumors, hematologic malignancies, autoimmune rheumatic disorders, bacterial infections, diabetes mellitus and nephropathy. We also found a significant positive correlation between urinary zinc and acute phase proteins alpha-1 acid glycoprotein (rs = 0.4649, P < 0.005), haptoglobin (rs = 0.4688, P < 0.005) and C-reactive protein (rs = 0.3636, P < 0.025), as well as a negative correlation with plasma zinc (rs = 0.3640, P < 0.025). As the role of lipid peroxidation in renal tubular cell injury has been proposed, the increased urinary levels of zinc, which has antioxidant properties, may be an important protecting mechanism, representing a part of the acute phase response in the kidney.