Messchendorp AL, et al. – Researchers examined the extent to which 300 patients with autosomal dominant polycystic kidney disease hyperfilter in this cross-sectional study. They measured GFR as urinary clearance using continuous infusion of ¹²⁵I-iothalamate. Hyperfiltration was defined by a loss of kidney function reserve capacity vs healthy control participants. Findings revealed that the increase in measured GFR after adding a dopamine infusion of 4.4–6 mg/h was determined as kidney function reserve capacity. In response to dopamine, GFR was increased among patients with early-stage ADPKD, either classified as having rapidly or slowly progressive disease. Hence, in ADPKD, hyperfiltration may not be an early phenomenon.