DIAGNOSTIC SIGNIFICANCE OF BETA 2-MICROGLOBULIN IN THE ASSESSMENT OF NEONATAL RENAL FUNCTION

Abstract

Serum and urinary beta 2-microglobulin (β2M) levels were measured by enzyme immunoassay in 28 normal neonates at days 1 to 2 and 3 to 4 of life in relation to gestational age (GA) and postnatal age (PNA). There were 10 preterm (P) and 18 term (T) infants with a mean GA of 34.5 and 39.1 weeks respectively. The serum β2M, glomerular filtration rate (GFR) and filtered load of β2M increased with increasing GA and PNA. No correlation was found between the serum β2M levels and the GFR as measured by endogenous creatinine clearance. Urinary β2M increased with increasing PNA. In both P and T infants the increase in β2M excretion paralleled an increase in filtered β2M. The β2M excretion in relation to GA showed a variable response. There was no correlation between serum and urinary β2M levels. Fractional excretion (%FE) β2M decreased as a function of both the GA and the PNA. A significant inverse correlation was found between %FE β2M and GA for infants <37 weeks, (r=0.9716, P<0.005). The fall in %FE β2M reached a plateau at 0.7% by 38 weeks of gestation. The highest %FE β2M (8.65%) was observed in infants of 32 weeks gestation, yet had the lowest filtered load of the protein. We conclude that 1) serum β2M level is a poor predicator of GFR in neonates <4 days of life. 2) glomerulotubular balance for β2M is established in infants with GA of 37 weeks or more. 3) %FE β2M can be used as a marker to assess the renal functional maturation in neonates in the early days of life.