Repeat testing is essential when estimating chronic kidney disease prevalence and associated cardiovascular risk

Investigations into chronic kidney disease (CKD) and cardiovascular disease in the CKD population may be misleading as they are often based on a single test of kidney function.

To determine whether repeat testing at 3 months to confirm a diagnosis of CKD impacts on the estimated prevalence of CKD and the estimated 10-year general cardiovascular risk of the CKD population.

Blood and urine samples from presumed healthy volunteers were analysed for evidence of CKD on recruitment and again 3 months later. Estimated 10-year cardiovascular risk was calculated using criteria determined by the Framingham study. Preliminary study: 512 volunteers were screened for CKD. Of the initial results, 206 indicated CKD or eGFR within one standard deviation of abnormal, and 142 (69%) of these were retested. Validation study: 528 volunteers were recruited and invited to return for repeat testing. A total of 214 (40.5%) participants provided repeat samples.

A single test indicating CKD had a positive predictive value of 0.5 (preliminary) and 0.39 (validation) for repeat abnormalities 3 months later. Participants with CKD confirmed on repeat testing had a significant increase in estimated 10-year cardiovascular risk over the population as a whole (preliminary: 16.5 vs. 11.9%, P < 0.05; validation: 18.1 vs. 9.2%, P < 0.01). Participants with a solitary test indicating CKD had no elevation in cardiovascular risk.

Repeat testing for CKD after 3 months significantly reduces the estimated prevalence of disease and identifies a population with true CKD and a cardiovascular risk significantly in excess of the general population.