What initial step should be taken in managing a patient with elevated calcium levels and normal laboratory findings aside from calcium?

When managing a patient with elevated calcium levels and normal laboratory findings aside from calcium, determining the underlying cause is critical for effective treatment. Measuring the serum parathyroid hormone (PTH) level is a crucial initial step.

In cases of hypercalcemia, the most common causes include primary hyperparathyroidism and malignancy. Checking the PTH level helps to differentiate between these conditions. If the PTH level is elevated or inappropriately normal despite high calcium, it suggests hyperparathyroidism. Conversely, if the PTH is low, it indicates the hypercalcemia is likely due to non-parathyroid causes, such as malignancy or other disorders.

Other options like discontinuing verapamil may be relevant if the medication is suspected to cause hypercalcemia, but determining PTH is more direct in identifying the etiology. A CT scan, while useful in certain contexts, is more appropriate after initial biochemical evaluations to identify possible malignancy or other anatomical issues. Genetic testing for multiple endocrine neoplasia type 1 is typically not warranted unless there are additional clinical features or family history indicative of this syndrome. Thus, measuring the serum PTH level is the most appropriate and useful initial step in this scenario.