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Urinary hydroxyproline in infants with and without fractures/rickets
W W Koo1, S K Krug Wispe, P Succop
1Department of Pediatrics, University of Alberta Hospitals, Walter Mackenzie Health Science Centre, Edmonton, Canada.
Insights
The urinary peptide-bound hydroxyproline to creatinine ratio is highest in early infancy for very-low-birthweight infants but not sufficient alone for detecting fractures or rickets. Bone turnover markers vary widely in these infants.
Area of Science:
- Biochemistry
- Pediatrics
- Neonatology
Background:
- Very-low-birthweight (VLBW) infants are susceptible to bone complications.
- Assessing bone turnover is crucial for managing VLBW infants.
Purpose of the Study:
- To measure urinary hydroxyproline to creatinine ratios in VLBW infants.
- To investigate the utility of these ratios in detecting fractures and rickets (F/R).
Main Methods:
- Urine samples were collected from VLBW infants at 3, 6, 9, and 12 months.
- Molar ratios of peptide-bound and free hydroxyproline to creatinine (OHPr:Cr) were analyzed.
- Infants were categorized into groups with (A) and without (B) F/R.
Main Results:
- Both peptide-bound and free OHPr:Cr ratios were highest at three months of age in both groups.
- Ratios decreased with postnatal age but showed no significant differences between groups.
- Wide variations in peptide-bound OHPr:Cr ratios were observed within groups.
Conclusions:
- Urinary peptide-bound OHPr:Cr indicates high bone turnover in early infancy for VLBW infants.
- This ratio alone is insufficient for detecting F/R in VLBW infants.
- The decrease in free OHPr:Cr ratio may reflect renal tubular function maturation.
Abstract:
Molar ratios of peptide-bound and free hydroxyproline:creatinine (OHPr:Cr) in urine were measured at 3, 6, 9, and 12 months of age in two groups of very-low-birthweight (VLBW less than or equal to 1500 g) infants. Group A (15 infants) had radiographically confirmed fractures and (or) rickets (F/R); Group B (17 infants) did not. The urinary peptide-bound OHPr:Cr ratio varied widely within groups and was greatest at three months in both groups: A = 0.81 +/- 0.45 and B = 0.55 +/- 0.32 (mean +/- SD). The ratio decreased with increasing postnatal age for each group but was not statistically different between groups throughout the study. The urinary free OHPr:Cr ratio also was greatest at age three months (A = 0.32 +/- 0.15 and B = 0.53 +/- 0.46), rapidly decreasing afterwards, and was not statistically different between groups throughout the study. We conclude that, in VLBW infants, bone turnover as indicated by the urinary peptide-bound OHPr:Cr ratio is highest during early infancy; however, the wide range of values for this ratio suggests that its use alone is not sufficient for detection of F/R in VLBW infants. The rapid decrease in free OHPr:Cr ratio is presumably related to the maturation of renal tubular function.