UNEXPECTED TUBULOINTERSTITIAL INVOLVEMENT IN GLOMERULAR DIEASE-DIAGNOSIS USING B2 MICROGLOBULIN

Abstract

Fractional excretion (FE) of B2 Microglobulin (B2M) was studied in children with glomerular (n=112) or tubular (n=77) diseases. FE-B2M (nl<0.4%) was significantly lower in glomerular diseases than in tubular lesions (0.17%±0.53% vs 16.7±23.5%: p<.001). Unexpectedly, several patients with glomerular diseases were found to have increased values for FE-B2M. To determine whether this was due to a tubular component in a primary glomerular disease process, FE-B2M was measured in 30 children, with various glomerulonephritides who underwent renal biopsy. The biopsy was reviewed, without knowledge of the FE-B2M results,for evidence of tubulointerstitial disease (TID). No patients were receiving drugs, or had other diseases, known to modify B2M excretion. FE-B2M in patients without biopsy evidence of TID was 0.10±0.02% (n=17): all values were in the normal range. FE-B2M in patients with biopsy evidence of TID averaged 16.3±29.3% (n=13); only 2 results were normal. There were patients with the same glomerular diseases in both groups. FE-B2M was used to follow successfully the course and treatment of a patient with membranous glomerulo-nephritis and an immunologically mediated Fanconi's Syndrome. These data demonstrate that TID occurs more often in apparently pure glomerular disease than has been recognized and that FE-B2M represents a reliable noninvasive method to diagnose such involvement. Preliminary data demonstrate that FE-B2M is of value in monitoring the progress and response to therapy in TID.

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