COMPARISON OF SECRETORY COMPONENT FOR IMMUNOGLOBULIN-A WITH ALBUMIN AS REFERENCE PROTEINS IN TRACHEAL ASPIRATE FROM PRETERM INFANTS

Objectives: To determine whether the concentration of secretory compon ent (SC) in tracheal aspirate samples is less altered by changes in al veolar-capillary permeability and thus is a more reliable reference st andard than albumin for the measurement of other components obtained b y saline lavage in preterm infants. Methods: A total of 1229 tracheal aspirate and 1530 blood samples were collected from 195 neonates to ev aluate the effects of advancing postnatal and gestational age, resolut ion of acute respiratory distress syndrome (RDS), steroid therapy for chronic lung disease, and acute sepsis on tracheal aspirate SC and alb umin levels. The tracheal aspirate and blood samples were analyzed by enzyme-linked immunosorbent assay techniques for SC and albumin concen trations. Results. The mean values for the concentrations of aspirate and plasma SC did not vary significantly during an 8-week study period (n = 100) and did not vary with either gestational age (23 to 36 week s) or postnatal age. Albumin concentration significantly decreased in aspirate samples from 1.67 +/- 0.77 mg/dl at week 1 to 0.41 +/- 0.21 m g/dl at week 8 (p <0.001), whereas serum levels increased from 2.65 +/ - 0.36 to 2.99 +/- 0.54 gm/dl (p <0.001), suggesting a decrease in alv eolar-capillary leakage with advancing postnatal age. The concentratio n of SC in aspirate samples from 51 infants who received dexamethasone remained constant during the first week of therapy, whereas the conce ntration of albumin decreased from 1.33 +/- 0.91 mg/dl at the initiati on of therapy to 0.51 +/- 0.34 mg/dl on treatment day 7 (p <0.001). Th e onset of sepsis (n = 40) was not accompanied by a significant change in either aspirate SC or albumin levels. However, in infants who had a deterioration in respiratory status concomitant with the onset of se psis (n = 10), the levels of aspirate albumin increased whereas serum levels decreased (p <0.001), suggesting an increase in alveolar-capill ary leakage; the levels of aspirate SC remained unaltered. Conclusions : Secretory component may serve as a more valid reference protein for the standardization of tracheal aspirate collection in preterm infants during evaluation of changes in inflammatory mediators in disease sta tes and therapeutic interventions that alter alveolar-capillary integr ity.