Urinary carnitine excretion in surgical patients on total parenteral nutrition.

Urinary free and total carnitine excretions were measured in 41 normal adults and seven surgical patients on fat-free total parenteral nutrition for 8 to 45 days. The means (+/-SEM) of urinary free and total carnitine excretion in normal adults were 162 +/- 19 and 328 +/- 28 micrometers/days, respectively. All of the patients exhibited protein-calorie malnutrition with a mean carnitine intake of 11.6 +/- 1.5 micrometers/day. Under this stringent carnitine economy with the adequate supply of lysine and methionine, urinary total carnitine excretion significantly reduced to 127 to 162 micrometers/day. This probably reflects the carnitine biosynthetic rate. However, during the periods of operation and/or infection, urinary total carnitine excretion significantly increased 2- to 7-fold that of normal levels. Significant positive correlation was found between the two forms of urinary carnitine and total nitrogen excretions. Serum free and total carnitine levels in patients were significantly higher than normal adults. Such findings can be explained by the endocrine responses to the stress phenomenon and indicate a catabolic response of skeletal muscle in which most of the body carnitine resides. This can impair their carnitine status.