Beta2-microglobulin in hypertensive pregnancies

Abstract

Beta2-Microglobulin (beta2-m) is a polypeptide that is freely filtered and then mostly reabsorbed and degraded in the proximal renal tubule. Beta2-m is a marker of glomerular filtration (GFR) in renal failure, whereas urinary beta2-m is a marker of proximal renal tubular dysfunction. Preeclampsia (PE) (ie, de novo hypertension in pregnancy with accompanying renal, cerebral, or liver disease or thrombocytopenia) often has renal involvement characterized by proteinuria, decreasing glomerular filtration, or renal tubular dysfunction. The aim of this study was to determine whether serum beta2- m concentration or urinary beta2-m excretion were greater in women with PE than in women with gestational hypertension (GH) (ie, isolated de novo hypertension in the second half of pregnancy) and normal pregnant women. Seventy-five pregnant women (35 with PE, 22 with GH, and 18 normotensives) were studied prospectively. Serum creatinine and beta2-m concentrations, 24-hour proteinuria, and fractional excretion (FE) of beta2-m were measured. Preeclamptics had similar serum creatinine but higher serum beta2-m (3.26+/-0.99 mg/L) than gestational hypertensives (2.44+/-0.77 mg/L; P = 0.016), and both groups had higher serum beta2-m than controls (1.62+/-0.54 mg/L; P = 0.001). FE of beta2-m was similar amongst groups (PE: 0.27%; interquartile range [IQR]: 0.20-0.86; GH: 0.21%; IQR: 0.11-0.40; controls: 0.26%, IQR: 0.12-0.69). PE is characterized by higher serum beta2-m but similar serum creatinine to GH. Because FE beta2-m is similar in these groups, this implies reduced filtering of beta2-m in PE rather than altered tubular handling of beta2-m. Further studies are now necessary to assess whether measurement of serum beta2-m is helpful in the clinical management of the hypertensive disorders of pregnancy. (Am J Kidney Dis 1998 Feb;31(2):308-12)