Plasma and red blood cell zinc in cystic fibrosis

The objectives of this study were to measure plasma and red blood cell (RBC) zinc concentrations in patients with cystic fibrosis (CF), and examine their relationship to nutritional status and pulmonary function. Plasma and RBC zinc levels were compared in 53 CF patients ranging in age from 0.5-46 years. Their relationships to weight (% ideal weight) and forced expired volume in 1 sec (FEV(1)) (% predicted value) were examined. After excluding improperly handled specimens, RBC zinc levels in 51 patients and plasma zinc concentrations in 40 patients were included for analysis. Sixteen of 51 (31%) patients had low RBC zinc levels compared to 4 of 40 (10%) with low plasma zinc concentrations (P < 0.01). Thirteen of 38 patients (34%) in whom both values were obtained had low RBC zinc concentrations compared to 4 of 38 (11%) with low plasma zinc levels (P < 0.022). Neither low RBC nor plasma zinc levels correlated with nutritional status or lung function. In conclusion, about one third of patients with CF had low RBC zinc levels. Plasma zinc concentrations may not adequately reflect overall zinc status. This deficiency did not appear to be related to either nutritional status or lung function. The significance of low RBC zinc in CF is unknown.