Validation and clinical utility of a novel immunoradiometric assay exclusively for biologically active whole parathyroid hormone in the horse.
BACKGROUND
Parathyroid hormone (PTH) plays a critical role in the regulation of mineral metabolism in mammals. Until recently, the standard method for PTH measurement has been the 2nd generation intact-PTH (I-PTH) assay. Current evidence indicates that the I-PTH assay binds to the PTH molecule and to an inactive N-terminally truncated PTH fragment that tends to accumulate in the blood of uraemic patients. Therefore, a new 3rd generation PTH assay that detects only the whole PTH molecule (W-PTH; cyclase-activating PTH [CAP]) has been developed.


OBJECTIVE
To validate this more specific W-PTH assay for measurement of equine PTH and evaluate its clinical utility.


METHODS
W-PTH and I-PTH were measured in plasma samples from normal horses (adults and foals) and horses with nutritional secondary hyperparathyroidism (N2HPT) and with chronic renal failure (CRF). Replicate measurements and dilutional paralellism were used for assay validation. Changes in blood ionized calcium were induced by EDTA and CaCl2 administration.


RESULTS
Performance of the W-PTH assay (accuracy, sensitivity, specificity and ability to detect changes in PTH in response to changes in calcium) was similar to that of the I-PTH assay. Surprisingly, the relative W-PTH concentration in normal horses and foals was higher than the relative I-PTH concentration. W-PTH values remained higher than I-PTH during acute hypo- and hypercalcaemia. An increase in both W-PTH and I-PTH concentrations was found in horses with N2HPT. In horses with CRF, W-PTH and I-PTH values were very low and no increase in I-PTH was observed.


CONCLUSIONS
The W-PTH assay can be used for measurement of equine PTH.


CONCLUSIONS
The use of W-PTH assay is likely to improve the diagnosis of mineral metabolism in horses.
Estepa
J C
JC
Departamento Medicina y Cirugia Animal, Universidad de Córdoba, Campus Universitario Rabanales, Ctra. Madrid-Cadiz km 396, 14014 Córdoba, Spain.
Garfia
B
B
Gao
P R
PR
Cantor
T
T
Rodriguez
M
M
Aguilera-Tejero
E
E
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000097:blood; D006734:Horse Diseases / Q000097:blood* / Q000175:diagnosis; D006736:Horses / Q000097:blood*; D006962:Hyperparathyroidism, Secondary / Q000097:blood / Q000175:diagnosis / Q000662:veterinary*; D015592:Immunoradiometric Assay / Q000592:standards / Q000662:veterinary*; D007676:Kidney Failure, Chronic / Q000097:blood / Q000175:diagnosis / Q000662:veterinary*; D010281:Parathyroid Hormone / Q000097:blood*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D010281:Parathyroid Hormone; D002118:Calcium