Methods: Six to eight urine portions were collected from one feeding to the next, which combined, resulted in a 24hr urine collection. Calcium excretion was measured in mmol/l and calculated into mg/kg.day (Reference 1-7 mg/kg.day). Calcium/creatinine ratios were estimated in mmol/mmol (Reference 0,3-2,2 mmol/mmol). Fourteen preterm born infants (gestational age < 34 weeks) were more than two weeks old at the time of urine collection.
Results: Mean gestational age was 28.9 weeks with a mean age of 55 days at the time of urine collection. No patient was hypocalciuric. In 4 hypercalciuric infants 26 urine samples were collected. The calcium/creatinie ratio of 11 samples (42%) was in the normal range, thus appeared to be false negatieve for the detection of hypercalciuria. In 10 normocalciuric infants 68 urine samples were collected of which 7 (10%) showed elevated calcium/creatinine ratios, so 10 % of the samples did not match the diagnosis normocalciuria.
[Calcium/creatinie ratio versus calcium excretion]
Conclusion: Calcium/creatinine ratios estimated in one urine sample inadequately reflect normo or hypercalciuria in preterm infants and should not be used for this purpose.
