Carnitine Status and Blood Ammonium Levels in Low Birth Weight Infants

Abstract

Forty‐three low birth weight infants appropriate for gestational age (AGA) were monitored to evaluate carnitine status in relation to blood ammonium levels. The infants were grouped into three depending on blood ammonium level on postnatal day 7:62.9 ± 3.8 μmol/L in group 1 (N =13), 38.9 ± 8.4 μmol/L in group 2 (N =23), and 24.5 ± 2.9 μmol/L in group 3 (N =9). Plasma free carnitine levels decreased in all three groups (p < 0.001) and plasma short chain acylcarnitine increased only in group 1 (p < 0.002), compared to findings in normal infants. The blood ammonium level positively and negatively correlated to plasma short chain acylcarnitine (p < 0.002) and plasma free carnitine levels (p < 0.002), respectively. The reabsorption rate of free carnitine in renal tubules (RRFC) was decreased at rates of 37.5, 27.5, and 25% of infants in groups 1, 2, and 3, respectively. The acylcarnitine/free carnitine clearance ratio (RAFCC) was decreased in groups 1 (p < 0.01) and 2 (p < 0.05) compared with group 3. Thus, an accumulation of short chain acyl moieties and insufficiency in renal absorption of free carnitine are putative causes of lowered plasma free carnitine in infants with higher blood levels of ammonium. The possibility that the carnitine status regulates blood ammonium levels in low birth weight infants warrants continued investigation.