Age- and height-adjusted total kidney volume growth rate in autosomal dominant polycystic kidney diseases

BackgroundThe Mayo Clinic Image Classification (MIC) was proposed as a renal prognosis prediction model for autosomal dominant polycystic kidney disease (ADPKD). MIC is based on the assumption of exponential constant increase in height-adjusted total kidney volume (HtTKV). HtTKV growth rate is calculated by one-time measurement of HtTKV and age. We named it as an age-adjusted HtTKV growth rate (AHTKV-). AHTKV- was compared with HtTKV slope measured by at least two HtTKV values.MethodsComparison of repeatability between AHTKV- and HtTKV slope, correlation of subgroups divided according to baseline AHTKV- and HtTKV slope with disease manifestations, estimated glomerular filtration rate (eGFR) slope, and renal survival were analyzed in 296 patients with ADPKD. PKD genotype influences were compared between AHTKV- and HtTKV slope in 88 patients with characterized PKD mutations.ResultsAbsolute differences between baseline and follow-up measures were significantly larger for the HtTKV slope than for AHTKV- (P<0.0001). From baseline AHTKV--based subgroups A-E according to MIC, disease manifestations occurred earlier and future eGFR slopes became steeper (P<0.0001). Multivariate hazard ratios of renal survival differed significantly among baseline AHTKV--based subgroups. Inter-subgroup differences in these predictors were less evident during baseline HtTKV slope-based classification. AHTKV- values, but not HtTKV slopes, were significantly higher for PKD1 mutation carriers than for PKD2 mutation carriers (P<0.0001).ConclusionMIC is a good renal prediction model applicable to Japanese patients also. AHTKV- can be a more sensitive and reliable indicator in TKV growth rate than HtTKV slope.