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

ABSTRACT

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.