Plasma uric acid level indicates tubular interstitial leisions at early stage of IgA nephropathy

BACKGROUND Hyperuricemia appeared to be a common symptom in IgA nephropathy (IgAN), even in those with normal eGFR. IgAN was characterized by variation of pathological features, especially variable tubulointerstitial lesions. Since tubular reabsorption and excretion appeared to be more important in determination of plasma uric acid levels in persons without obvious decrease of glomerular filtration rate, we took advantage of our IgAN cohort to investigate whether plasma uric acid level associated with tubular interstitial lesions, and could be considered as a maker for tubular interstitial lesions, especially at early stage with normal eGFR. METHODS 623 IgAN patients were involved in the present study. Morphological changes were evaluated with Oxford classification scoring system as well as Beijing classification system of IgAN. Statistical analysis was done with SPSS 13.0. RESULTS We found that plasma uric acid level associated with percentage of interstitial fibrosis/tubular atrophy. Higher plasma uric acid levels indicated higher tubulointerstitial scores, either with Oxford system (P = 0.012) or with Beijing classification system (P = 4.8*10-4) in the whole cohort. We also found that in the subgroup of 258 IgAN cases with normal baseline eGFR (eGFR > =90 ml/min/1.73 M2), higher plasma uric acid associated with more severe tubulointerstitial lesions with Beijing scoring system (P = 3.4*10-5). The risk of having more than 10% tubulointerstitial lesions in patients with hyperuricemia increased 58% compared with normal uric acid level. In subgroup with normal eGFR, only hyperuricemia predicted tubulointerstitial leisions, and the risk of having more tubulointerstitial changes increased 100%. Among these patients, hyperuricemia was associated with more tubulointerstitial lesions with a specificity of 60.3%. Specificity increased to 65% among those patients with eGFR > =90 ml/min/1.73 m2. CONCLUSIONS Plasma uric acid levels indicate tubular interstitial lesions in IgAN and hyperuricemia may be considered as a marker for tubulointerstitial lesions.