The definitive test for hypoparathyroidism is evaluating a serum PTH concentration and a concurrent ionized calcium concentration.1,4 With a normal functioning parathyroid gland, PTH should be increased in response to a low ionized calcium concentration.2 An animal with hypoparathyroidism will have an inappropriately low serum PTH concentration (undetectable to low-normal)
with a low ionized calcium concentration.2,7 So it is essential to perform both tests on the same blood sample. Serum samples should not be kept at room temperature
for longer than two hours before they are refrigerated or frozen.7,8 Contact the laboratory for guidelines on handling samples before collecting them because incorrectly handled samples may
yield erroneously low results.8
TREATMENT
Table 1: Treatment of Primary Hypoparathyroidism
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Table 1 provides an overview of the treatment recommendations for patients with primary hypoparathyroidism.
Initial treatment
Typically, affected animals are hospitalized for treatment because they require intensive care and frequent re-evaluation.
Animals with tetany or seizure activity may respond to empirical administration of diazepam.1,3 With prolonged tetany, animals may become hyperthermic. As muscle relaxation occurs with treatment, a gradual normalization
of body temperature occurs and additional cooling measures are typically not necessary.1-3 Serial monitoring of body temperature is recommended.3
When hypocalcemia has been established to be the cause of tetany, administer a slow intravenous bolus of a calcium salt.1,2 Ten percent calcium gluconate provides 9.3 mg/ml elemental calcium and is the preferred calcium salt because it is not irritating
if accidentally injected perivascularly.1-3 The dosage of 10% calcium gluconate is 0.5 to 1.5 ml/kg (5 to 15 mg/kg) over 10 to 30 minutes, to effect.1-3,10 An alternative calcium salt is 10% calcium chloride, which contains 27.2 mg/ml elemental calcium.1,2 However, because of its higher calcium concentration, calcium chloride is more likely to cause severe tissue trauma and
calcinosis cutis if injected perivascularly.1-3,11 The calcium salt must not be diluted in fluids that contain lactate, acetate, bicarbonate, or phosphates because calcium
precipitation will occur, but 0.9% sodium chloride solution is appropriate.1-3
Monitoring an electrocardiogram (ECG) for potential cardiac arrhythmias is important during initial treatment for hypocalcemia
because, when present, the arrhythmia may temporarily worsen. Various arrhythmias may occur with low ionized calcium concentrations,
including bradycardia, tachycardia, and heart block.12 Because of the prolonged action potential in cardiac cells, the S-T and Q-T segments are often prolonged, with deep and
wide T waves.1,3,12 Bradycardia, sudden elevation of the S-T segment, shortening of the Q-T interval, or ventricular premature complexes during
administration all indicate cardiotoxicity from the calcium infusion,1-3 and the intravenous infusion should be temporarily stopped. When the ECG normalizes, reinstitute the infusion at a slower
rate if further administration is needed to control tetany. The dosage provided above is a guideline only; the patient's response
(resolution of neuromuscular signs) should guide individual dosing.1,3
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