Direct equilibrium dialysis compared with two non-dialysis free T4 methods in premature infants.

OBJECTIVE: To compare the incidence of low free T4 values reported by a direct equilibrium dialysis method to their incidence reported by 2 non-dialysis methods. STUDY DESIGN: Ninety-five infants, < or = 33 weeks gestational age at birth, admitted to Loma Linda University Children's Hospital before day 3 of life were studied. Infants were grouped by gestational age ranges: < or = 27, 28-30, and 31-33 weeks. Free T4 determinations were measured at 3, 7, and 14 days of life with 3 different free T4 methods. Gestational age-specific newborn reference ranges were available for the direct equilibrium dialysis method only. The only reference ranges available for the non-dialysis free T4 methods were not gestational age specific. Using available reference ranges we classified free T4 values as either low or not low. The incidence of low free T4 values was compared at 3, 7, and 14 days of life. RESULTS: Low direct equilibrium dialysis free T4 values were substantially less frequent than non-dialysis free T4 values. CONCLUSION: Substantial free T4 inconsistencies occur between dialysis and non-dialysis free T4 methods in preterm infants. It is unclear how much of this inconsistency is method dependent and how much is reference range dependent.

Incidence of low free T4 values in premature infants as determined by direct equilibrium dialysis.

BACKGROUND: The incidence of transient reductions in serum free T(4) (FT(4)) in premature infants may be overestimated because certain FT(4) analytical methods underestimate FT(4) concentrations. Transient reductions of FT(4) measurements have been reported in the majority of premature newborn infants. Direct equilibrium dialysis (DED) does not underestimate FT(4) concentrations and is the best available technique to measure serum FT(4) in the premature infant. OBJECTIVE: To evaluate the incidence of low FT(4) concentrations in premature infants using DED to measure FT(4). DESIGN/METHOD: We measured FT(4) by DED in infants with birth weight <1500 g. Infants were excluded if the following conditions were present: congenital anomalies or maternal thyroid disorders. Free T(4) was measured at 14 days of life. Low FT(4) was defined using a statistical definition of FT(4) measurements <10.3 pmol/l (0.8 ng/dl). RESULTS: Free T(4) was measured by DED in 114 infants. Low FT(4) levels were seen in nine infants (7.9%). CONCLUSION: The incidence of low FT(4) was much lower than previously reported when FT(4) was measured using DED indicating that methodological issues are involved in the variability among estimates of the frequency of transient reduction in FT(4).

Comparison of 2 iron doses in infants receiving recombinant human erythropoietin therapy.

OBJECTIVE: To compare iron sufficiency in premature infants receiving high-dose recombinant human erythropoietin (r-HuEPO), 1200 IU/kg per week, supplemented with 6 or 12 mg/kg per day of enteral iron. DESIGN: We conducted a prospective, double-blind, controlled study of premature infants receiving r-HuEPO therapy, randomly assigned to receive 2 different doses of iron. Measurements of ferritin, iron, total iron-binding capacity, reticulocyte count, hemoglobin level, and hematocrit were obtained at baseline, 4, and 6 weeks. Transferrin saturation was calculated; the number of blood transfusions and the incidences of sepsis were recorded. SETTING: This study was performed in the neonatal intensive care unit at Loma Linda University Children's Hospital, Loma Linda, Calif. SUBJECTS: Infants with a gestational age of 32 weeks or younger, older than 7 days, and receiving r-HuEPO therapy from March 1, 1997, to June 30, 1998, were eligible for the study. Infants were randomly assigned to receive 6 mg/kg per day or 12 mg/kg per day of enteral iron during a course of r-HuEPO therapy for 4 to 6 weeks. RESULTS: Sixty-four infants were enrolled in the study. Twelve infants did not complete the study; 52 completed 4 weeks and 41 completed 6 weeks of the study. While ferritin levels and transferrin saturation decreased in both groups over the study period, there were no differences between the 2 study groups. CONCLUSIONS: Infants receiving high-dose r-HuEPO therapy (1200 IU/kg per week) decrease their ferritin levels (measure of iron stores) even when receiving high enteral iron supplementation. Given that the ferritin levels were similar between the 2 groups, we speculate that the additional iron either was not absorbed or was not stored.

QTc interval in infants receiving cisapride.

OBJECTIVE: To examine the effect of cisapride on the corrected QT (QTc) interval in infants over a 14-day period. STUDY DESIGN: A prospective cohort study of infants receiving cisapride (0.8 mg/kg per day). Twelve-lead electrocardiograms were obtained before and 3, 5, 7, and 14 days after cisapride initiation. RESULTS: Fifty infants completed the study; none had arrhythmias. Fifteen of 50 infants (30%) developed QTc interval > or =450 msec; QTc interval normalized in 13 of 15 infants. Infants with QTc interval on day 3 > or =2 standard deviations above the mean baseline QTc interval (401+40 msec) were more likely to develop prolonged QTc interval (p<0.0001). CONCLUSION: QTc interval prolongation was noted in 30% of infants. Subsequently, the majority of those infants had QTc interval normalization by day 14 of cisapride therapy. QTc interval 3 days following cisapride initiation may identify infants at risk for transient QTc interval prolongation. With appropriate monitoring, hospitalized infants receiving cisapride may have improved gastrointestinal motility without cardiac morbidity.