CLINICAL EVALUATION ON QUANTITATION OF SERUM AND URINARY

β₂-MICROGLOBULIN, ESPECIALLY AS AN INDEX OF RENAL TUBULAR FUNCTION

Abstract

The concentration of the low molecular weight protein β₂-microglobulin was measured by radioimmunoassay (Phadebas_® β₂-Micro Test) in human serum and urine from 19 normal subjects, 29 patients with impaired renal function, 13 acute pyelonephritis, 2 chronic pyelonephritis, 6 female acute cystitis and 29 patients under treatment of hemodialysis.
The present study was designed to observe the changes of serum and urinary β2-microglobulin concentration according to the decreasing renal function and/or renal tubular function.
Results are as follows:
1) Normal value of serum β₂-microglobulin level was 1.9±1.0mg/l (m±2 S.D.), with the upper limit of 2.9mg/l. Normal urinary β₂-microglobulin level was 86±96ug/l (m±2 S.D.), and with the upper limit of 182μg/l.
2) Good correlation was observed between serum β₂-microglobulin level and values of some renal function tests; correlation coefficients were 0.81 (between serum β₂-microglobulin and BUN), 0.80 (serum creatinine), -0.67 (24 hour creatinine clearance), 0.76 (PSP₆₀), and -0.81 (between log serum β₂-microglobulin and log 24 hour creatinine clearance).
These findings suggest that serum β₂-microglobulin level is well reflected by GFR (24 hour creatinine clearance) or RPF (PSP₆₀) and that the measurement of serum β₂-microglobulin may be one of the useful parameters for the evaluation of renal function, without urine collection.
3) In two cases of acute renal failure, the changes of serum β₂-microglobulin level were in parallel with the values of some renal function tests and the clinical course. Therefore, it seems that the serum β₂-microglobulin level indicates the degree of renal damage and that its measurement is of use for diagnosis and evaluation of acute renal failure.
4) A remarkably high urinary β₂-microgloblin excretion, although the serum level is within the normal limit, was demonstrated in the acute stage of acute pyelonephritis. In the convalescent stage, urinary β₂-microglobulin level decreased to almost normal level.
The ratio of β₂-microglobulin clearance to creatinine clearance (Cβ_2-MG/Ccr) also presented the same changes in acute and convalescent stage. Therefore, the reabsorption of β₂-microglobulin seems to be disordered in the acute stage.
Maximum urinary osmolality in the acute stage of acute pyelonephritis was significantly lower than that of normal control. We conclude that the distal and proximal renal tubular dysfunction is present in the acute stage of acute pyelonephritis.
5) Serum β₂-microglobulin level in patients under treatment of hemodialysis was as extremely high as 48.9±28.6mg/l (m±S.D.) and urinary level was also as high as 3377±1852ug/l (m+S.D.).
6) In this study, we used the index of Cβ_2-MG/Ccr. (ratio of β₂-microglobulin clearance to creatinine clearance) to exclude the influence of urinary volume to the urinary β₂-microglobulin concentration. And this index seems to present the filtration fraction of β₂-microglobulin per nephron, or excretion rate of β₂-microglobulin. Localization of the renal dysfunction, namely the difference between the specific tubular dysfunction and tubular dysfunction associated with the damage of total nephron, may be revealed clearly by observing the relationship of Cβ₂/Ccr. and Ccr.
We have concluded in this paper that β₂-microglobulin excretion rate (Cβ₂/Ccr.) is an index for the renal tubular, especially proximal tubular function.