Mortality at low and high estimated glomerular filtration rate values: a 'U' shaped curve

While a low estimated glomerular filtration rate (eGFR) confers an increased risk of dying, the mortality associated with high eGFR values has not been ascertained.

Four variable MDRD-derived eGFR was calculated in a total of 33,386 patients (18,620 F, 14,766 M) aged > or =50 years (median 68 years, IQR 60-76 years) collected by family doctors in 2000. They were then classified according to their eGFR into 30 ml/min/1.73 m(2) bands (<30, 30-59, 60-89, 90-119, 120-150). The subsequent mortality status of each patient was determined at 31st December 2006 and cause of death recorded where available.

Applying Cox proportional hazards models (adjusted for age and gender), the hazard ratio (HR) of dying compared to a reference of patients with eGFRs of 60-89 ml/min/1.73m(2) was, as expected, higher in the low eGFR bands (HR 1.37 (95% CI 1.29-1.45) for 30-59; HR 2.60 (2.31-2.93) for <30 ml/min/1.73 m(2), both p < 0.0001). However, it was also greater amongst patients with higher eGFRs (HR 1.29 (1.19-1.41) for 90-119; HR 2.63 (2.16-3.21) for 120-150 ml/min/1.73 m(2), p < 0.0001). Circulatory disease was the main cause of death in patients with low eGFRs and respiratory disease/cancer, in patients with high eGFRs.

As a marker of mortality, both low and high eGFRs are equally predictive of increased mortality in community patients, exhibiting a 'U' shaped curve. Thus, current CKD guidelines which recommend inaction or even the non-reporting of eGFR values greater than 60-90 ml/min/1.73 m(2) may not identify patients who are at an equally high risk of dying as those where intervention is recommended.