Deficiency of Vit. C in infant is best estimated by Vit. C level in –

Leukocyte vitamin C Leukocyte concentration of vitamin is a better indicator of body store, it may be deficient even in the absence of clinical signs of deficiency. It is estimated by buffy coat preparation. ​ Plasma vitamin C Plasma ascorbic and levels vary widely and cannot be relied upon to detect early vitamin C deficiency. Urinary vitamin C Saturation of the tissues with vitamin C can be estimated from the urinary excretion of the vitamin after a test dose of ascorbic acid. Excretion of 80% of the test dose in the urine within 3-5 hr after parenteral administration is considered to be normal. In vitamin C deficiency, less than 80% of test dose is excreted.