<prompt> Deficiency of Vit. C in infant is best estimated by Vit. C level inPlasmaUrinary excretionBuffy coat estimationAdrenal cortical Vit. C estimation  <response>: Leukocyte vitamin CLeukocyte 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 CPlasma ascorbic and levels vary widely and cannot be relied upon to detect early vitamin C deficiency. Urinary vitamin CSaturation 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. 