Systematic review of the evidence underlying the association between mineral metabolism disturbances and risk of all-cause mortality, cardiovascular mortality and cardiovascular events in chronic kidney disease.

BACKGROUND: Chronic kidney disease (CKD) is a powerful risk factor for all-cause mortality and its most common aetiology, cardiovascular (CV) mortality. Mineral metabolism disturbances occur very early during the course of CKD but their control has been poor. A number of studies have assessed the relationship between all-cause mortality, CV mortality and events with mineral disturbances in CKD patients, but with considerable discrepancy and heterogeneity in results. Thus, a systematic review was conducted to assess methodological and clinical heterogeneity by comparing designs, analytical approaches and results of studies.
METHODS: Medline, EMBASE and Cochrane databases were systematically searched for articles published between January 1980 and December 2007.
RESULTS: Thirty-five studies were included in the review. All-cause mortality was the most commonly assessed outcome (n = 29). Data on CV mortality risk (n = 11) and CV events (congestive heart failure, stroke, myocardial infarction) (n = 4) are limited. The studies varied in populations scrutinized, exposure assessments, covariates adjusted and reference mineral levels used in risk estimation. A significant risk of mortality (all-cause, CV) and of CV events was observed with mineral disturbances. The data supported a greater mortality risk with phosphorus, followed by calcium and parathyroid hormone (PTH). The threshold associated with a significant all-cause mortality risk varied from 3.5-3.9 mg/dL (reference: 2.5-2.9) to 6.6-7.8 mg/dL (reference: 4.4-5.5) for high phosphorus, <3 mg/dL (reference: 5-7) to <5 mg/dL (reference: 5-6) for low phosphorus, 9.7-10.2 mg/dL (reference: < or =8.7) to >10.5 mg/dL (reference: 9-9.5) for high calcium, < or =8.8 mg/dL (reference: >8.8) to <9 mg/dL (reference: 9-9.5) for low calcium and >300 pg/mL (reference: 200-300) to >480 pg/mL (reference: < or =37) for PTH. Thresholds at which the CV mortality risk significantly increased were >5.5 (reference: 3.5-5.5) and >6.5 mg/dL (reference: <6.5) for phosphorus and >476.1 pg/mL (reference: <476.1) for PTH.
CONCLUSIONS: Serious limitations were observed in the quality and methodology across studies. In spite of enormous heterogeneity across studies, a significant mortality risk was observed with mineral disturbances in dialysis patients. Data on risk in pre-dialysis patients were less conclusive due to even more limited (numerically) evidence.