TUBULAR DYSFUNCTION IN INFANTS WITH MECONIUM STAINED AMNIOTIC FLUID - DIAGNOSIS USING B2 MICROGLOBULIN

Abstract

Urinary concentrations of B2 microglobulin (B2M) and creatinine were measured in normal term infants and in those born with meconium stained amniotic fluid (MEC). None of the infants or their mothers had conditions known to modify B2M excretion. Apgar scores for the normal and MEC infants averaged 8.8 and 7.7 respectively at 1 min and 9.0 and 8.2 at 5 min. Urinary B2M to creatinine levels (mg/gm) increased significantly (p<.01) in the normal infants from day 1 (1.5±1.3:n=29) to day 3 (3.5±2.8:n=21) of life. Compared to the normals, values for the MEC infants were significantly increased (4.7±0.6:n=25:p<.005:day 1 and 12.9±8.9: n=26:p<.005:day 3). Values in 12 of 25 MEC infants on day 1 and 13 of 26 on day 3 exceeded 2 SD above the normal mean. Urinary creatinine excretion was similar in the normal and MEC infants. We propose the increase in B2M levels from days 1 to 3 in normal infants is due to an increased glomerular filtration rate, increasing the filtered load. The elevated levels in the MEC infants indicates the existence of tubular dysfunction, probably mild acute tubular necrosis, in these infants even though other clinical evidence for this lesion was absent. This data supports the concept that MEC reflects stress in these neonates and indicates that urinary excretion of B2M is an extremely sensitive, noninvasive method for detecting even mild tubular damage in these patients. The existence of tubular injury in a high percentage of this patient population has not previously been suspected.