Radioimmunoassay for parathyroid hormone in equids.

The research explored the application of a radioimmunoassay, a scientific method to measure certain substances, for parathyroid hormone (PTH) in equids like horses. The research was extended to both healthy and disease-affected equids, and the assay was found reliable for equine carboxy-terminal PTH.

Objective and Methods

• The research aimed to gauge the viability of a radioimmunoassay for PTH in equids, more specifically in horses.
• To achieve this, the researchers used blood samples collected from both healthy equids and those suffering from conditions like hypercalcemia and hypophosphatemia. Hypercalcemia is an abnormally high calcium level in the blood, whereas hypophosphatemia indicates lower than normal phosphate levels.

Results

• The researchers validated the assay for equine carboxy-terminal PTH, indicating that the test is reliable for this specific element of the PTH.
• The manipulation of serum ionized Calcium (Ca) in healthy equids effected an anticipated increase and decrease in measurable immunoreactive PTH levels. This was achieved by infusion of Disodium Ethylenediaminetetraacetic Acid (Na2 EDTA) – which is known to reduce Calcium levels, and Calcium Chloride (CaCl2) – which increases the calcium level.
• The intra-assay and interassay coefficients of variation were determined at 2.6% and 11.7%, respectively, indicating a low level of variability within a given assay and higher variability between different assays.

Findings

• The range of PTH valves for healthy mature equine mares and geldings maintained on pasture was found to be between 0.27 ng/ml to 0.92 ng/ml and for horse colts fed grain was 0.61 to 1.25 ng/ml.
• PTH values were measured on two equine patients with hypercalcemia, one pony with primary hyperparathyroidism, and one horse with pseudohyperparathyroidism. Both patients exhibited increased serum PTH levels, thereby demonstrating that the assay could accurately indicate elevated PTH in diseased states.

Conclusion

• This research indicates that the radioimmunoassay for PTH could be a viable tool for detecting and monitoring PTH levels in horses, particularly in identifying abnormal levels associated with health issues like hypercalcemia, hypophosphatemia, primary hyperparathyroidism, and pseudohyperparathyroidism.