The Angiotensin Converting Enzyme (ACE) in Serum test is used to measure the level of ACE in the blood. This test helps evaluate the function of the renin-angiotensin system, which plays a crucial role in regulating blood pressure. It may assist in diagnosing conditions such as hypertension, sarcoidosis, and certain lung diseases. A blood sample is typically taken in the morning, and it is important to follow the doctor's instructions for preparation before the test.