The prognostic role of estimated glomerular filtration rate (eGFR) is well established. However, the extent to which eGFR adds to risk prediction conditioned to the type of BP measurement is not known. Ambulatory blood pressure (ABP) is a stronger predictor of cardiovascular (CV) events than clinic BP (CBP), and the prognostic impact of eGFR relative to ABP seems blunted in general population studies.
We recorded incident cardiovascular (CV) events in 7141 never treated hypertensives recruited in 8 centers worldwide (Australia, Italy, Japan, and U.S.A) who had baseline measurements of eGFR, CBP and ABP. We computed adjusted hazard ratios (HR) for CV outcome events in relation to eGFR using separate Cox models for CBP and ABP while adjusting for age, gender, smoking, diabetes, and total cholesterol. We estimated the added predictive value of eGFR using the continuous Net Reclassification Improvement (cNRI) and the relative Integrated Discrimination Improvement (rIDI).
At baseline examination the eGFR was lower than 60 ml/min/1.73m2 in 11% of patients. During a mean follow-up of 6 years (41445 patient-years of total exposure) we recorded 610 fatal and non-fatal CV events. In multivariable models, eGFR was a significant predictor of CV events when added to models including either CBP or ABP. The estimated HR for 10 ml/min/1.73m2 eGFR reduction was 1.15 [95% CI 1.09-1.21] (p<0.001) and 1.14 [95% CI 1.08-1.20] (p<0.001) for CBP and ABP models respectively. After adding eGFR to CBP the events and non-events correctly reclassified were 7% and 8% respectively (cNRI=0.15; rIDI 8.9%; p<0.001). For ABP the proportions correctly reclassified were somewhat lower, 5% and 6% for events and non-events respectively, but still significant (cNRI=0.11; rIDI 5.6%; p<0.001).
In conclusion, eGFR is an independent and additive risk factor to either CBP or ABP and refines CV risk stratification to a highly significant extent in never treated hypertensives,
Adjusted hazard ratio for cardiovascular events by type of systolic blood pressure measurment and eGFR strata