Obesity, Hyperparathyroidism Linked in CKD
Elevated intact parathyroid hormone also associated with low albumin and elevated CBC count.
Elevated BMI is associated with secondary hyperparathyroidism in non-dialysis CKD patients, especially patients who have evidence of malnutrition and inflammation, a study found.
"We knew that in people with normal kidney function obesity leads to impairment in vitamin D metabolism and elevated PTH levels, but this phenomenon was never studied in patients with CKD," said lead investigator Csaba P. Kovesdy, MD, of the Salem Veterans Affairs Medical Center in Salem, Va.
"Since both obesity and hyperparathyroidism are very complex problems in CKD, establishing an association between the two is important because of potential prognostic and therapeutic implications."
He and his colleagues examined the association between intact parathyroid hormone (iPTH) level and BMI in 496 men with CKD (stages 2-5) not yet on dialysis. The men had a mean age of 69.4 years, and 113 (22.8%) were black. The study population had a mean estimated glomerular filtration rate of 31.8 mL/min per 1.73 m2.
The investigators, who published their findings in the Clinical Journal of the American Society of Nephrology (2007;2:1031-1036), divided the men into four groups according to BMI: less than 25, 25-28, 28.1-33, and greater than 33 kg/m2. Patients in these groups had iPTH levels of 84, 92, 102, and 105 pg/mL, respectively, after adjusting for age, race, diabetes status, and serum calcium and phosphorus levels.
The researchers also looked at the influence of serum albumin and white blood cell (WBC) count—both surrogate markers of malnutrition and inflammation. For patients with albumin levels of 3.6 g/dL or less, iPTH levels were 84, 96, 116, and 123 pg/mL for those whose BMI was less than 25, 25
.-28, 28.1-33, and greater than 33 kg/m2, respectively. The trend was statistically significant in this group but not in the group with albumin levels above 3.6 g/dL, in which the iPTH levels were 79, 85, 78, and 79 pg/mL, respectively.
Among patients with a mean WBC count above 7,200/mL, iPTH levels increased with higher BMI quartiles, a trend that was statistically significant. This was not the case among patients whose mean WBC count was 7,200/ml or less.