Relationship between Plasma Zinc and Red Blood Cell Zinc Levels in Hospitalized Patients

Patient zinc stores are quantified with plasma or red blood cell (RBC) measures. The relationship between these 2 measures of zinc status has not been determined in a broad population of hospitalized patients.

Both plasma zinc and RBC zinc were prospectively collected and measured in 252 consenting patients admitted urgently to hospital. Plasma and RBC zinc levels were measured within 48 h of admission. We collected demographic, vitals, and laboratory data for use in multivariate regression models that included markers of acute disease severity and systemic inflammation.

Plasma zinc and RBC zinc levels were low in 63% and 10% of hospitalized patients, respectively. Categorized zinc levels based on normal intervals for plasma and RBC zinc values were not related (χ2 0.47 [2 df] P = 0.79). The Pearson correlation coefficient between plasma zinc and RBC zinc was -0.09 (P = 0.15). After adjustments for multiple clinical covariates, the correlation coefficient remained insignificant (r = -0.11, P = 0.08). Plasma zinc was inversely associated with markers of inflammation including the neutrophil-to-lymphocyte ratio and temperature.

Patient-specific plasma and RBC zinc are unrelated in hospitalized patients, possibly due to decreased values with acute illness seen in the former but not the latter. Future studies are required to determine which of these measures best predicts outcomes in hospitalized patients.