Sex Differences in Urinary Alpha-1-Microglobulin Value in Normal Individuals

Yoshihisa Itoh, Department of Clinical Pathology, Jichi Medical School, Minami-Kawachi-Machi, Tochigi-Ken 329-04 (Japan) Dear Sir, αpMicroglobulin (αrm), a brown-colored low-molecular weight (LMW) glycoprotein of 30 kD, has unique physicochemical properties and suppresses leukocyte migration [1,2]. Two molecular forms are found at varied ratios in serum: one is a free form (LMW αrm); the other is an IgAbound form (IgA-αrm complex) [3]. Because of the selectivity of the glomerular basement membrane, αrm found in urine is LMW αrm. Clinical studies indicate that the main catabolic site for LMW α‚-m is in the renal proximal tubules [4–6]. Another reliable double-antibody radioimmunoassay for αrm, based on a previously established radioimmunoassay method [7], has been developed recently. Its sensitivity is 20 ng/ml, and the assay time when undiluted samples are used is only 2 h. In the course of evaluating this assay, we coincidentally discovered a sex-related difference in the αrm value in normal urine. Thus, we investigated it in some detail. Serum and 24-hour stored urine specimens obtained from 17 normal males and females ranging from 20 to 30 years of age were paired. The quantity of αrm excreted during a 24-hour period was greater in males than in females (p < O.Ol; table 1). On a simple anatomical basis, the correction for body surface area gave only an 18% increase in the αrm level in females, leaving an average discrepancy of 1,36 mg of excreted αrm per day. Similar 1 Supported partly by a grant-in-aid from the Ministry of Education for Scientific Research (Project No. 62480435) and a research grant from the Tochigi Association for Preventive Nephrology (1988). A radioimmunoassay kit (AMG RIA) was supplied from Shionogi & Co., Ltd. (Osaka, Japan). The authors are grateful to the staff of the Serological Diagnostic Section in the Department of Clinical Laboratory, Jichi Medical School, and Kanagawa Yobo Igaku Kyokai (Yokohama, Japan) for supplying sera. results were obtained when kidney weight was corrected for, leaving about a 7% increase, indicating that the differences are accounted for by physiological variation. Prefiltered load of serum LMW α‚-m on the kidneys was analyzed chromatographically. Each pooled-serum sample was diluted five times with 0.05 M phosphate buffer (pH 7.2), gel-filtered on Superose 6 and Superose 12 using FPLC system (Pharmacia, Sweden), and the concentration of αi-m in each fraction was measured by RIA. Fractionation had good reproducibility, and recovery from 80 to 85% when those fractions in which the αrm concentration was below the minimum required by the test were excluded. In accordance with previously reported results [3], serum αrm centered