What would be an expected lab finding in a patient taking lithium?

In a patient taking lithium, hypercalcemia is a pertinent finding that may occur due to lithium's effects on parathyroid hormone regulation and calcium homeostasis. Lithium can lead to increased calcium release from bones and modifications in renal handling of calcium, potentially resulting in elevated serum calcium levels.

This is especially important because lithium can cause a condition resembling primary hyperparathyroidism due to its influence on parathyroid glands. In examining further details related to the other options: increased renal function typically does not correlate with lithium therapy; rather, lithium is known to potentially impact renal function adversely over long-term use. Hypoglycemia is unrelated to lithium treatment, as it does not typically cause low blood sugar levels. Decreased TSH levels would denote suppressed thyroid function, which could happen, but it is more common for lithium to lead to hypothyroidism, not decreased TSH, as it can inhibit thyroid hormone synthesis.

Therefore, hypercalcemia is the most expected lab finding among patients on lithium due to its unique interaction with calcium metabolism.