Premature infants undergo intensive growth during the postnatal period. Adequate mineralization is dependent on sufficient intake of
calcium (Ca) and
phosphorus (P). However, Ca and P supplementation can be associated with some risks, for example development of
nephrocalcinosis. We investigated pathophysiological risk factors in premature very low birth weight (VLBW) infants associated with the development of
nephrocalcinosis. From June 1994 to September 1995 all preterm neonates with a
birth weight below 1,500 g were screened prospectively. At regular intervals of 2 weeks, ultrasonography (US) of the kidneys was performed and parameters of
mineral metabolism were assessed in blood and spot urine samples. For analysis, premature infants with
nephrocalcinosis (group N) were compared with infants without
nephrocalcinosis (group R) and with a retrospectively pair-matched subgroup of premature infants without
nephrocalcinosis (control group C) taken from the same study.
Nephrocalcinosis was detected in 20 of 114 preterm neonates (group N, 17.5%). Of these 20 infants with
nephrocalcinosis, 16 presented with a tendency towards systemic
acidosis (pH<7.25) on day 2-7, compared with only 4 of 20 premature infants of the control group. Premature infants of group N had a lower serum P at 2 weeks of life and 5 (versus 0 patients of the control group C) had transient
hypophosphatemia (serum P<1.6 mmol/l). Moreover, the Ca/
creatinine ratio in spot urine specimens tended to be higher (P<0.1) in patients developing
nephrocalcinosis. There were no significant differences in the duration of ventilation, the
length of stay in the intensive care unit, and duration and frequency of
furosemide and
steroid treatment between the groups N and C. VLBW premature infants developing
nephrocalcinosis frequently presented with slightly impaired
acid-base homoeostasis within the 1st week, followed by signs of impaired mineralization (and immature or impaired renal function) within 2 weeks. In VLBW premature infants, close observation of
acid-base status and regular analysis of spot urine specimens (Ca, P,
creatinine) during the first weeks of life may help to identify those premature infants at risk for
nephrocalcinosis.