Insights into nutritional and inflammatory aspects of low parathyroid hormone in dialysis patients

In individuals with advanced chronic kidney disease, secondary hyperparathyroidism is known to be associated with high turnover bone disease. Low serum parathyroid hormone (PTH) levels may not necessarily be because of hypodynamic bone, but could be another facet of the malnutrition-inflammation-cachexia syndrome (MICS). A recent 5-year cohort study in 748 stable hemodialysis outpatients showed that after the confounding effect by the MICS was removed, the moderately low levels of PTH in the 100 to 150 pg/mL range was associated with the greatest survival rate. Data from Japanese dialysis patients show similar survival advantages of having a lower PTH range. Low levels of serum PTH seem to be associated with markers of protein-energy wasting and inflammation, and this association may confound the relationship between serum PTH and alkaline phosphatase. PTH stimulates lipogenesis through influx of calcium into the adipocytes. PTH secretion is suppressed by interleukin-1 beta and interleukin-6, which are proinflammatory cytokines that are associated with poor outcome in dialysis patients. These cytokines inhibits PTH secretion in cultured parathyroid tissue slices. In this article, we review the association of a low serum PTH level with the MICS in patients with chronic kidney disease and suggest avoiding over-interpretation of low serum PTH level as an indicator of low turnover bone disease.