Calcium Infusion Test for Medullary Cancer of the Thyroid

INDICATIONS

Suspected acalcitoninaemia.
Suspected medullary carcinoma of thyroid.
Screening of families with medullary carcinoma of the thyroid.
Patients with suspected MEN type 2.

CONTRAINDICATIONS

Bleeding disorders

SIDE EFFECTS

Unpleasant flushing sensation
No major side effects

PREPARATION

Patient should fast overnight.
Check electrolytes and serum calcium.
Cannula, 19g.
Saline flush.
Calcium gluconate 10% (10 - 20 ml required).
6 x Lithium heparin tubes (green top Vacutainer) with 200 µl Trasylol.
Syringes.
Ice and facilities to transfer samples immediately to lab.

METHOD

Insert cannula and flush.
Take baseline sample for calcitonin.
Give calcium gluconate 0.2 ml/kg body weight i.v. over 1 minute.
Flush cannula.
Take samples at 1, 2, 3, 5 and 10 minutes for calcitonin.
Send immediately on ice to the lab for centrifugation and freezing.

INTERPRETATION

In medullary carcinoma of the thyroid there is often a raised fasting serum calcitonin (>90 ng/l) but this may be in the normal range. Provocative tests improve the sensitivity of calcitonin measurement. Normal range for peak calcitonin following calcium infusion is 100 to 200 ng/l

SENSITIVITY AND SPECIFICITY

In the study quoted below 8/12 subjects with medullary thyroid carcinoma had increased responses to calcium infusion. Two of the four who failed to respond had a raised baseline calcitonin. There is a high false positive rate especially in young men. The pentagastrin test is better in this situation.

REFERENCES

Charib H. et al., Mayo Clinic Proc., 62, 373 (1987).