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

BACKGROUND: 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. AIM: 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. DESIGN AND METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Single estimated glomerular filtration rate and albuminuria measurement substantially overestimates prevalence of chronic kidney disease.

BACKGROUND/AIMS: Guidelines require repeatedly diminished estimated glomerular filtration rate (eGFR) and/or albuminuria to diagnose chronic kidney disease (CKD), and advise screening only in select populations. Many estimates of CKD prevalence have used single measurements. This longitudinal study assessed eGFR and albuminuria reproducibility, and impact on estimate of CKD prevalence, in factory workers. METHODS: A total of 512 white workers in a Belarusian industrial factory were initially tested, identifying 206 with abnormal (eGFR <59 ml/min/1.73 m(2) or albuminuria) or near-abnormal (eGFR up to 1 SD above abnormal) renal function. At 3 months, 142 of the abnormal/near-abnormal cohort were re-tested. RESULTS: Analysis of repeat samples revealed no significant change in eGFR in this population, however 21% individually changed CKD stage. Initial proteinuria was reproducible in only 48% at 3 months. This had a major impact on estimated CKD prevalence: a point prevalence of 8.2% halved with repeat testing. The predictive value of initially abnormal eGFR or albuminuria for repeat abnormality at 3 months was 0.5. CONCLUSION: Non-targeted screening for CKD is inaccurate and can overestimate prevalence. This study emphasises the importance of confirming abnormal eGFR and proteinuria on at least one further sample 3 months apart before categorising the individual as having CKD. This has wide implications for screening in European general populations.