Renal dysfunction detected by beta-2 microglobulinuria in sick neonates.

OBJECTIVE To assess renal involvement in sick neonates referred to Neonatal Intensive Care Unit (NICU) using standard renal parameters and urinary beta 2 microglobulin (B2M) excretion. DESIGN Descriptive study. SETTING Level II NICU and Nephrology Division of Pediatric Tertiary hospital. SUBJECTS Forty six term sick neonates transferred for neonatal care and forty healthy term neonates who served as normal controls for urinary B2M excretion. METHODS Standard tests including estimation of BUN, serum creatinine, blood pH, serum bicarbonate, serum and urinary electrolytes, urine output, and urinalysis. Urinary B2M levels were estimated from urine collected on day 1 (D1) and day 3 (D3) in all and 18 neonates were tested on day 7 (D7) by radio-immunoassay method. RESULTS Statistically significant elevation of mean values of urinary B2M were noted when sick neonates were compared with normal controls irrespective of primary disease, indicating tubular dysfunction (41/46 = 90%), whilst only 7 of these (17%) had abnormalities indicating renal involvement when judged by standard tests. Very high levels of urinary B2M were noted with birth asphyxia (n = 9), sepsis (n = 8) and renal disease (n = 7). Transient elevation of urinary B2M was noted in meconium aspiration syndrome (n = 4). Ten surgical cases with non renal congenital malformations showed high urinary B2M and 12/18 tested on D7 had persistently high urinary B2M due to multiple factors. CONCLUSIONS Elevated urinary B2M in 90% sick neonates with apparently normal renal parameters in majority (34/41) indicates subclinical proximal tubular dysfunction especially in neonates with asphyxia, sepsis and congenital malformations. Persistent elevation of urinary B2M appear to be a sensitive diagnostic indicator for defining a group of neonates with subtle renal tubular dysfunction, the clinical relevance of which on long term basis is a subject for future study.