Renal zinc clearance/glomerular filtration rate ratio as an indicator of marginal zinc deficiency associated with iron deficiency in childhood.

Objective: To evaluate the usefulness of renal zinc clearance/glomerular filtration rate ratio (R(ClZn)/GFR) as an indicator of marginal zinc deficiency that is generally associated with iron deficiency in childhood.
Methods: Zinc status was evaluated in 36 iron-deficient children (22 boys and 14 girls) who ranged in age from 1 to 10 years using serum zinc concentration and U(Zn/Cr) and R(ClZn)/GFR ratios. The results were compared with the zinc status of 36 similar-aged healthy children (24 boys and 12 girls).
Results: Serum zinc concentrations were 96.72 +/- 2.13 microg/dL and 93.93 +/- 1.95 microg/dL in iron-deficient and healthy subjects, respectively (p > 0.05). U(Zn/Cr) ratios were 0.54 +/- 0.04 microg/mg and 0.88 +/- 0.04 microg/mg (p < 0.0001); R(ClZn)/GFR ratios were 2.27 x 10(-3) +/- 0.20 and 3.32 x 10(-3) +/- 0.20 (p < 0.001) in iron-deficient and healthy subjects, respectively. Individual values of R(ClZn)/GFR and U(Zn/Cr) ratios correlated with hemoglobin (Hb) concentrations (r = 0.34, p < 0.01 and r = 0.26, p < 0.05). Data grouped according to the ranges of Hb concentrations and R(ClZn)/GFR and U(Zn/Cr) ratios fit the following equations: The statistically significant difference in U(Zn/Cr) and R(ClZn)/GFR ratios between groups indicates decreased urinary estimation of marginal zinc deficiency, whereas no change was observed in serum zinc concentrations. According to the regression equation, it can be postulated that the R(ClZn)/GFR ratio is a linear function of Hb concentration and the U(Zn/Cr) ratio.
Conclusion: R(ClZn)/GFR ratio was a reliable indicator for reduction in urinary zinc excretion; it estimated the marginal zinc deficiency associated with iron deficiency. The R(ClZn)/GFR ratio can be calculated using one sample of blood and urine; thus it could serve as an alternative indicator of marginal zinc deficiency, especially in routine health care.