Useful indicators for performing renal biopsy in adult patients with isolated microscopic haematuria

Among adult patients with isolated microscopic haematuria (IMH) which is defined as persistent microscopic haematuria but without proteinura, hypertension, renal insufficiency, urinary tract infection or structural abnormality of the urinary tract, some patients have chronic glomerulonephritis (CGN), in whom early diagnosis by renal biopsy is beneficial to timely intervention. Nevertheless, a considerable number of patients with optimistic prognosis [e.g. thin basement membrane nephropathy (TBMN)] undergo invasive and needless renal biopsy. Indicators for weighing the necessity of renal biopsy would be clinically significant. To investigate the value of urinary albumin/creatinine ratio (UACR), serum IgA level, serum C3 level and serum IgA to C3 ratio in predicting the necessity of renal biopsy for adult patients with IMH, 216 patients were studied retrospectively. Patients were divided into: (CGN group, n = 137), (TBMN group, n = 56) and normal biopsy (normal group, n = 23). Of all patients, 131 (61%) evidenced microalbuminuria (UACR = 30-299 mg/g) and 85 (39%) had normoalbuminuria (UACR < 30 mg/g). The mean value of UACR in CGN group was higher (96 +/- 17 mg/g) compared with that in TBMN (20 +/- 4 mg/g, p < 0.01) or normal (18 +/- 3 mg/g, p < 0.01) group. The mean values of serum IgA and serum IgA/C3 ratio in patients with IgA nephropathy (IgAN) were significantly higher than those with non-IgAN (380 +/- 103 : 217 +/- 99 mg/dl, p < 0.01; 4.5 +/- 1.2 : 2.4 +/- 0.9, p < 0.01). The odds ratio for distinguishing IgAN from non-IgAN was significantly correlated with serum IgA level and serum IgA to C3 ratio. For adult patients with IMH, UACR, serum IgA level and serum IgA to C3 ratio are non-invasive markers for predicting the necessity of renal biopsy.