Human α ₁ -Microglobulin and Its Relationship to Renal Function

To evaluate the clinical usefulness in terms of estimation for glomerular filtration rate (GFR), we determined the levels of α₁-microglobulin (α₁m) in the serum and urine of patients with various renal diseases and compared with those of β₂-microglobulin (β₂m) and creatinine. Serum and urinary α₁m levels were measured by using single-radial immunodiffusion method. 24-hour creatinine clearance (Ccr) was used as a indicator of GFR. There was a significant positive correlation between serum α₁m and creatinine levels (r = 0.75, p < 0.001). Serum α₁m, β₂m and creatinine inversely correlated and logarithmically correlated to Ccr as shown in the following equations: log α₁m = 2.30 – 0.42 × log Ccr (r = – 0.74); log β₂m = 2.06 – 0.91 × log Ccr (r = – 0.92); log creatinine = 1.57 – 0.78 × log Ccr (r = – 0.94). Both correlation coefficient and regression coefficient for α, m were rather poor compared to those for β₂m and creatinine. However, α₁m levels started to increase over normal range when Ccr fell below 80 liters/day, while β₂m and creatinine remained within normal ranges.The daily urinary excretion of α₁m was increased in the patients whose Ccr was within normal limits compared to that of healthy control subjects (15.2 ± 3.2 mg/day, n = 19, vs. 5.7 ± 0.7, n = 7, p < 0.001). Fractional clearance of α₁m increased proportionally to the decrease of Ccr. These data suggest that combined measurements of α₁m in the serum and urine seem to be useful to estimate GFR, especially to detect the mild reduction of CFR.