Red cell sorbitol concentration in relation to short- and medium-term variation of plasma glucose

To evaluate the time course of changes in red cell sorbitol (RCS) concentration in relation to variations of plasma glucose levels, RCS was determined in 7 normal subjects during i.v. glucose infusion (IVGTT); in 6 hyperglycemic insulin-dependent diabetic subjects while glycemia was normalized with Biostator GC 115 and in 4 diabetic patients in previously poor metabolic control, in whom normal glycemia was obtained in 8-10 days by intensive insulin therapy. During IVGTT, plasma glucose levels increased with significant differences from baseline at 5, 10, 16, 25, 60, 100 and 160 min and returned to basal levels after 3h; RCS concentration showed small and insignificant increases. During i.v. insulin infusion, plasma glucose fell to almost normal levels within roughly 3h; RCS levels showed a gradual reduction becoming significant at 180 min. In the third study, decrease in plasma glucose was always associated with a fall in RCS level which became significant between the 2nd and the 3rd day of the study. Thus, RCS levels were not affected by very short-term variations of glycemia but by a previous hyperglycemic crisis that lasted a few hours. There were therefore medium-term variations of RCS level. In conclusion, RCS determination is not useful as an index of metabolic control in diabetes.