PREVALENCE OF SECONDARY HYPERPARATHYROIDISM IN DIALYSIS PATIENTS: COMPARISON BETWEEN BIOCHEMICAL AND MORPHOLOGICAL DIAGNOSIS

Patients with Chronic Kidney Disease (CKD) can develop secondary hyperparathyroidism (sHPT), which is an adaptive response triggered by persistent alterations of the mechanisms that control the homeostasis of calcium (Ca), phosphorus (P) and vitamin D. In epidemiological studies, the prevalence of sHPT is based on mineral metabolism biochemical parameters and on serum intact parathyroid hormone (i-PTH) levels. Based on these parameters, the prevalence varies from 20-30% to 47-50%. The primary objective of this study was to establish the epidemiology of a cohort of maintenance hemodialysis (MHD) and peritoneal dialysis (PD) patients. Secondary objectives of the study were: 1) to integrate the biochemical and pharmacological data with the morphological data obtained by Ultrasonography with colorDoppler (US/CD) and 2) to establish the correlation between morphological and biochemical sHPT. We enrolled 395 patients, 269 males and 126 females, 380 in MHD and 15 in PD. All patients underwent US/CD examination of the thyroid/parathyroid glands. The examination was performed by two experienced operators; single-blind (ICC 0.95-intrapersonal, interpersonal-ICC 0.91). Epidemiological data were collected in a case report format. Mean dialytic age of population studied was 62.9 ± 71.3 months while mean predialytic CKD age was 91.4 ± 82.7 months. Serum Ca was 8.9 ± 0.8 mg / dl, P 4.7 ± 1.5 mg / dl, Ca x P product 41.8 ± 15.0 mg2/dl2, ALP 133.5 ± 93.1 IU/l and i-PTH 281.9 ± 233.4 pg/ml. The prevalence of biochemical sHPT was 36.2% (143 patients out of 395) while the prevalence of morphological sHPT was 27.3% (108 patients out of 395). According to the reference values recommended by the K-DOQI guidelines, 252 patients showed i-PTH serum levels ≤300 pg/ml (144.1 ± 78.9 pg/ml) and 143 patients had i-PTH serum levels >300 pg/ml (526.6 ± 215.9 pg/ml). Serum Ca levels did not differ significantly while P, Ca x P product and ALP were significantly different (P 4.6 ± 1.4 mg/dl vs 4.9 ± 1.7 mg/dl, p = 0.03, Ca x P 40.5 ± 13.8 mg2/dl2 vs 44.4 ± 16.6 p = 0.01, ALP 124.7 ± 87.2 IU/l vs 148.9 ± 101.1 IU/l, p=0.01). US/CD showed 173 parathyroid glands in 108 patients: 70 (64.9%) of them showed values of i-PTH >300 pg/ml and 38 (35.1%) values of i-PTH ≤300 pg/ml. 73/287 (25.4%) patients showed values of i-PTH >300 pg/ml, without hyperplastic parathyroid glands at US/CD. The correlation between i-PTH and gland volume showed a linear trend (R2 = 0.1365, p = 0.001) regardless of current treatment (glandular volume = 0.8995 * (i-PTH) + 15.3). The biochemical evaluation associated with morphological examination with US/CD is the most complete diagnostic protocol for sHPT. So if i-PTH is constantly >400-500 pg/ml, an US/CD evaluation of the neck should be performed in order to document the presence of hyperplastic glands.