Independent effects of secondary hyperparathyroidism and hyperphosphataemia on chronic kidney disease progression and cardiovascular events: an analysis from the NEFRONA cohort

Background Secondary hyperparathyroidism (SHPT) is a complication of chronic kidney disease (CKD) and is associated with changes in calcium and phosphate. These related changes have been associated with increased cardiovascular mortality and CKD progression. It is not clear whether negative outcomes linked to SHPT are confounded by such factors. The present study was designed to assess the possible independent effects of SHPT [defined as patients with excessive parathyroid hormone (PTH) levels or on treatment with PTH-reducing agents] on the risk of CKD progression and cardiovascular event (CVE) incidence in CKD patients, as well as whether hypercalcaemia and/or hyperphosphataemia act as effect modifiers. Methods The study enrolled 2445 CKD patients without previous CVE from the National Observatory of Atherosclerosis in Nephrology (NEFRONA) cohort (Stage 3, 950; Stage 4, 612; Stage 5, 195; on dialysis, 688). Multivariate logistic and Fine and Gray regression analysis were used to determine the risk of patients suffering CKD progression or a CVE. Results The prevalence of SHPT in the cohort was 65.6% (CKD Stage 3, 54.7%; CKD Stage 4, 74.7%; CKD Stage 5, 71.4%; on dialysis, 68.6%). After 2 years, 301 patients presented CKD progression. During 4 years of follow-up, 203 CVEs were registered. Patients with SHPT showed a higher adjusted risk for CKD progression and CVE. Furthermore, hyperphosphataemia was shown to be an independent risk factor in both outcomes and did not modify SHPT effect. No significant interactions were detected between the presence of SHPT and hypercalcaemia or hyperphosphataemia. Conclusions We conclude that SHPT and hyperphosphataemia are independently associated with CKD progression and the incidence of CVE in CKD patients.