Developmental changes in urinary coproporphyrin ratio in premature infants

Background Premature infants have a high concentration of conjugated bilirubin in their blood, although they have a poor glucuronide conjugation of bilirubin. This may be due to developmental changes in the function of adenosine triphosphate binding cassette subfamily C member 2, which is involved in the cellular export of conjugated bilirubin. In the present study, we examined the developmental changes in the urinary coproporphyrin I/(urinary coproporphyrin I+ urinary coproporphyrin III) ratio (UCP (I/ [I + III])), a known biomarker for adenosine triphosphate binding cassette subfamily C member 2 function, in premature infants. Method Twenty‐one premature infants born between 25 and 32 weeks of gestation were included in the study. Urine samples were collected within 24 h of birth, and at 1 week and 3–4 weeks after birth. The samples were analyzed by high‐performance liquid chromatography to calculate UCP (I/ [I + III]) to examine its association with postnatal age and corrected gestational age. Subjects were excluded if they had liver dysfunction, cholestasis, urinary tract infection, or chromosomal abnormalities. Results The average UCP (I/ [I + III]) within 24 h of birth, at 1 week, and at 3–4 weeks after birth was 0.84, 0.61, and 0.65, respectively. The UCP (I/ [I + III]) within 24 h of birth was significantly higher than that measured at 1 week or 3–4 weeks after birth. There was no significant correlation between UCP (I/ [I + III]) and the corrected gestational age. Conclusion The UCP (I/ [I + III]) was higher within 24 h of birth. It decreased 1 week after birth and remained low without any significant changes for up to 4 weeks after birth.