Factors associated with progression of IgA nephropathy are related to renal function--a model for estimating risk of progression in mild disease.

BACKGROUND: A number of factors are linked to the outcome of IgA nephropathy (IgAN). However, it has been difficult to compare results of studies since patient populations have varied greatly. There were 3 aims in the study reported here, namely to compare factors associated with renal outcome in IgAN patients with different levels of renal function on diagnosis; to determine factors which were independently associated with progression of renal disease in initially mild IgAN; and to create a model for the estimation of the risk of progression in individual IgAN patients with normal renal function on diagnosis.

METHODS: Two hundred and fifty-nine IgAN patients who had been followed on average for 9.1 (SD 4.5) after diagnosis were divided into 2 groups on the basis of renal function on diagnosis. In group 1 (98 patients), Ccr (creatinine clearance, estimated by the Cockcroft-Gault formula) was < 85 ml/min, in group 2 (161 patients) > or = 85 ml/min. Univariate analyses were used to find significant differences between progressors and non-progressors in both groups. Logistic regression analysis was used to determine factors independently associated with progression in group 2.

RESULTS: Several factors were found to be associated with outcome in both groups, such as hypertension, level of Ccr, serum cholesterol, proteinuria, and also histopathological changes. Factors associated with progression in patients with initially decreased renal function (group 1), were predictable, such as male sex, absence of episodes of macroscopic hematuria, serum urate level and degree of tubular atrophy. Surprisingly, in patients with initially normal renal function (group 2), numbers of urinary erythrocytes were associated with outcome. The factors independently associated with progression in this group were number of urinary erythrocytes, existence of hypertension and in histopathology arteriolosclerosis and the level of glomerular score. A model for estimating risk of progression on the basis of various combinations of factors found to be independently associated with outcome is presented.

CONCLUSIONS: We concluded that association between variable and outcome in IgAN depends partly on renal function at the time of assessment of the factor. Since there are factors which are independently associated with the outcome of early and apparently mild disease, early diagnosis of IgAN is desirable: outcome in mild IgAN can be predicted reliably on the basis of factors found to be independently associated with outcome.