Low Vitamin D, High PTH Up Mortality Risk in Early CKD

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The risk for premature death increased by 62% and 42% for stage 3 CKD patients with vitamin D deficiency and elevated parathyroid hormone levels, respectively.
The risk for premature death increased by 62% and 42% for stage 3 CKD patients with vitamin D deficiency and elevated parathyroid hormone levels, respectively.

Vitamin D deficiency and elevated levels of parathyroid hormone (PTH) are independent risk factors for death among patients with stage 3 chronic kidney disease (CKD), a new study confirms. Increased levels of fibroblast growth factor 23 (FGF23) are not a risk factor.

During 5 years of follow-up of the Renal Risk in Derby study, 289 of 1664 stage 3 CKD patients (mean age 73) died. The causes of death were cardiovascular for 101 patients, malignancy for 75, infection for 61, other causes for 41, and unknown for 11. The risks for all-cause mortality were increased by 62% and 42% for those with vitamin D deficiency (below 25 nmol/L) and elevated PTH levels (above 65 pg/mL), respectively.

Unlike some previous studies, FGF23 showed no significant correlation with premature death. “While FGF23 may have a role as a risk marker in high-risk populations managed in secondary care, our data suggest that it may not be as important in CKD stage 3, managed in primary care,” Adam Shardlow, MD, of Royal Derby Hospital, in Derby, United Kingdom, and colleagues wrote in BMJ Open. Patients were treated at 32 primary care practices in Derby.

The investigators also examined CKD progression, defined as a 25% fall in estimated glomerular filtration rate (eGFR) and a drop in GFR category, or an increase in albuminuria category. FGF23, vitamin D, and PTH did not appear to be associated with CKD progression in multivariable models.

The FGF23 findings contrast with results from CRIC (Chronic Renal Insufficiency Cohort). The team cited a number of differences between the studies that might explain disparities, such as the relatively preserved renal function, older age, less severe albuminuria, and lower diabetes prevalence in their study. In addition, median FGF23 was notably lower compared with CRIC.

Dr Shardlow and his colleagues suggested treating vitamin D deficiency might improve survival of early stage CKD patients.

In a discussion of study limitations, the researchers noted that low event rates for CKD progression and cardiovascular mortality may have led to underpowering.

Reference

Shardlow A, McIntyre NJ, Fluck RJ, McIntyre CW, and Taal MW. Associations of fibroblast growth factor 23, vitamin D and parathyroid hormone with 5-year outcomes in a prospective primary care cohort of people with chronic kidney disease stage 3. BMJ Open. doi: 10.1136/bmjopen-2017-016528

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