Elevated urinary C-peptide excretion in multiple trauma patients

A simple, indirect method of estimating integrated insulin secretion is the measurement of C-peptide, a byproduct of insulin biosynthesis, in plasma and in 24-hr urine samples. We determined, in 29 severely injured hypermetabolic and highly catabolic multiple trauma patients, the plasma level and daily excretion rate of C-peptide, 48-72 hrs postinjury. Data from a set of eight patients who underwent glucose-based total parenteral feeding for 6 days were analyzed for the course of changes in the excretory pattern of C-peptide and catecholamines. The molar ratio of plasma C-peptide to insulin in the trauma patients was similar to that in unstressed controls, indicating that the rate of hepatic insulin extraction is not appreciably altered due to trauma. This is also evident from a significant correlation (p = 0.001) between the plasma C-peptide and insulin levels. The excretion of C-peptide was elevated to three times the normal both in absolute terms and when normalized to creatinine excretion. This was also accompanied by a twofold increase in the plasma levels, indicating an enhanced secretion rate of C-peptide and hence of insulin in response to trauma. Injury-induced insulin resistance does not seem to be due to a decreased insulin secretion. An increase in insulin output would appear to be a significant and desirable response for a continued anabolic stimulus coexistent with the net catabolic phase. Parenteral feeding augmented the excretion of C-peptide and catecholamines and this effect peaked on the fourth day of nutritional therapy.