Serum surfactant protein D as a marker for bronchopulmonary dysplasia.

BACKGROUND: Lung epithelial cells express surfactant protein D (SP-D), a calcium-dependent lectin that plays an important role in antibody-independent pulmonary host defense. Previous studies have shown that it is found in the peripheral circulation in patients with pulmonary disease, likely because of translocation into the blood when lung epithelial barriers are disrupted by inflammation or acute injury. In adults, serum SP-D levels are biomarkers for the progression and severity of chronic lung disease. In neonates, elevated SP-D levels in cord blood and on day 1 have been associated with prenatal risk factors and with an increased risk of respiratory distress syndrome and infections. It is not known whether serum SP-D during the first week of life is a marker for bronchopulmonary dysplasia (BPD), a form of chronic lung disease of prematurity that is associated with lung parenchymal maldevelopment and injury.

OBJECTIVE: The goal of this study is to determine whether serum SP-D on days 3 and 7 of life are associated with the development of BPD in preterm infants.

DESIGN/METHODS: Serum samples were obtained on postnatal days 3 and 7 from 106 preterm infants (500-2000 g birth weight, 23-32-week gestation). SP-D was quantified by Western blot. BPD was determined at 36 weeks PMA using NICHD criteria.

RESULTS: The mean birth weight was 1145 ± 347 g and gestational age 29.2 ± 7.4 weeks. BPD was diagnosed in 7 and "BPD or death" in 16 infants. Days 3 and 7 values tracked significantly (r = 0.648), and did not correlate with birth weight or gestational age. Contrary to expectations, serum SP-D was not associated with BPD. Significant gender differences were noted, with SP-D dropping from day 3 to day 7 in males, while increasing in females (p < .05).

CONCLUSION: Elevated serum SP-D does not appear to be a useful marker for BPD. Decreasing serum SP-D levels in males, as compared to females, during the first week of life are likely related to gender differences in lung maturation, consistent with the higher incidence of BPD in males.