This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Which of the following is used to differentiate between hypercalcemia of malignancy from primary hyperparathyroidism? 
Select and explain. 
A. Hydrocoisone suppression test, B. Glucose challenge test, C. 24 hour urine calcium measurement, D. Percentage of ionized calcium
A: Hydrocoisone suppression test
Answer: A: Hydrocoisone suppression test 
Explanation: Answer- A. Hydrocoisone suppression testlf doubt exists, hyilrocokone suppression test is of value.If the test is performed as originally described, (120 mg hydrocoisone per day for 10 days, correcting the serum calcium for haemodilution), it provides an excellent discrimination, since significant suppression ofserum calcium does not occur in primary hyperparathyroidism, where as malignant hypercalcemia is usually completely alleted.