Changes in plasma and buffy layer vitamin C following surgery.

Postoperative changes in plasma and buffy layer (BL) vitamin C were studied in 107 patients receiving either 0 (37 patients), 100 mg (33 patients) or 500 mg (37 patients) vitamin C supplements daily. In patients receiving no supplement plasma vitamin C concentrations had fallen (mean 33 per cent) by the first postoperative day and thereafter changed little. The falls occurred irrespective of initial plasma concentration, were greater the higher the initial concentration, but tended to be proportional to the length of operation. In patients given supplements this loss of vitamin C was evident but modified, and from the second postoperative day the response to the supplements was as would have been expected in non-operated subjects. The most probable explanation for the loss of vitamin C from plasma was an increased urinary excretion during operation. Changes in BL vitamin C concentrations were studied in relation to changes in leucocyte and platelet counts. The previously reported postoperative falls in BL vitamin C were found to be the result of a major artefact in the methods routinely used for BL vitamin C estimation, caused by changes in the leucocyte and platelet populations, most importantly the platelet to leucocyte ratio. No true demand for vitamin C, as measured from the buffy layer cells, was evident.