Markers of type I and III collagen turnover as indicators of growth velocity in very low birth weight infants

Monitoring postnatal growth in very low birth weight (VLBW) infants is comp licated by the difficulty of obtaining reliable measurements. A need thus e xists for safe and reliable indicators of such infants' short-term growth v elocity. We set out to study whether markers of type I collagen synthesis [ aminoterminal propeptide of type I procollagen (PINP)] or degradation [via the matrix metalloproteinase pathway, carboxyl-terminal telopeptide of type I collagen (ICTP)] or of type III collagen synthesis [amino-terminal prope ptide of type III procollagen (PIIINP)] could serve as such indicators. PINP, ICTP, and PIIINP were measured for 48 VLBW infants (mean birth weight , 923 g; range, 540-1485 g; mean gestational age, 27.6 wk; range, 23.7-32.7 wk) at the age of 1, 2,4, and 8 wk. At each time point, these were compare d with concurrent growth velocity rigorously assessed by frequent lower leg (knemometry) and weight measurements. PINP showed a significant positive correlation with lower leg growth veloci ty at 1, 2, and 4 wk and with weight growth velocity at 2, 4, and 8 wk. PII INP showed a significant positive correlation with lower leg growth at 1, 2 , and 8 wk and with weight growth at 2 and 8 wk. The ICTP/PINP ratio, refle cting type I collagen degradation in relation to its synthesis, showed clos e negative correlations with lower leg growth at 1 wk (r = -0.46; P=0.003), 2 wk (r = -0.51; P=0.002), and 4 wk (r = -0.56; P=0.001) and with weight gr owth at 2 wk (r = -0.39; P=0.018), 4 wk (r = -0.59; P=0.0003), and 8 wk (r = -0.53; P=0.005). A high ICTP/PINP ratio was an accurate predictor of impa ired growth; a high ICTP/PINP ratio was a more rapid and at least as sensit ive and specific indicator of slow growth as weight gain. We conclude that PINP, PIIINP, and the ICTP/PINP ratio all reflect postnata l growth velocity in VLBW infants. The most robust of these indicators is t he ICTP/PINP ratio, which may thus serve as a clinical tool in assessing sh ort-term growth of these infants.