The Angiotensin-Converting Enzyme (ACE) blood test measures the level of this enzyme circulating in the bloodstream. Healthcare providers generally order this test when they suspect a patient has a medical condition causing widespread inflammation and involving the formation of small clumps of immune cells. The test quantifies the enzyme present in a blood sample, assisting in the evaluation of disease activity and providing insight into certain disease processes.
The Role of the Angiotensin-Converting Enzyme
Angiotensin-Converting Enzyme is a protein that plays a key role in the body’s system for regulating blood pressure and fluid balance, known as the Renin-Angiotensin System (RAS). The enzyme is primarily found on the surface of endothelial cells lining blood vessels, with high concentrations in the capillaries of the lungs and kidneys.
ACE converts the inactive hormone precursor, Angiotensin I, into the active hormone, Angiotensin II. Angiotensin II is a potent vasoconstrictor, causing the walls of small arteries to tighten and narrow. This constriction increases resistance to blood flow, leading to a rise in blood pressure. ACE also degrades bradykinin, a peptide that promotes vasodilation and lowers blood pressure.
Why Doctors Order the ACE Test
The ACE test is primarily used to help diagnose and monitor sarcoidosis, an inflammatory disease. Sarcoidosis is characterized by the formation of granulomas—tiny clusters of immune cells—which most often affect the lungs and lymph nodes. The cells forming these granulomas often produce and secrete excessive amounts of ACE into the bloodstream.
Elevated ACE levels are found in approximately 50 to 80 percent of patients with active sarcoidosis. Monitoring these levels over time helps assess disease severity and treatment effectiveness, such as with corticosteroids. If a patient’s ACE level decreases, it may indicate that the sarcoidosis is entering remission or responding well to therapy.
While sarcoidosis is the main indication, the ACE test may also be ordered when a provider suspects other conditions that cause elevated levels, such as Gaucher disease or certain types of liver disease. The test is a useful tool for investigating unexplained symptoms common to systemic inflammatory disorders, including persistent cough, shortness of breath, joint pain, or skin lesions.
Preparing For and Performing the Test
The procedure for an ACE blood test is straightforward, involving a simple venipuncture to collect a blood sample. A phlebotomist typically draws blood from a vein in the arm, usually near the elbow. The process takes only a few minutes before the sample is sent to a laboratory for analysis.
Patient preparation sometimes involves specific instructions to ensure accurate results. Some laboratories request fasting, meaning refraining from eating or drinking anything other than water for up to 12 hours before the draw.
It is important to discuss all current medications with the ordering physician, as certain drugs can interfere with the ACE measurement. This is particularly true for ACE inhibitor medications, prescribed for high blood pressure and heart failure, which artificially lower the measured ACE level by blocking enzyme activity. Steroid medications, such as prednisone, can also suppress enzyme production and may require temporary discontinuation prior to the test.
Interpreting ACE Test Results
Interpreting the results of an ACE blood test requires understanding the established reference range, which represents the normal concentration of the enzyme expected in a healthy adult. This range can vary slightly depending on the laboratory and the specific method they use to measure the enzyme, but generally, levels are reported in units such as nanomoles per milliliter per minute (nmol/mL/min). An adult reference range is often cited as being below a certain threshold, such as 40 or 50 units, though the lab report will always provide its specific normal values.
An elevated ACE level suggests increased enzyme production, which can be highly suggestive of active sarcoidosis, especially when accompanied by compatible clinical symptoms and imaging findings. However, a high result is not a definitive diagnosis for sarcoidosis because the enzyme can also be elevated in various other conditions, creating a risk of a false positive result. These conditions include alcoholism-related liver disease, hyperthyroidism, diabetes, and certain types of cancer like Hodgkin disease.
Conversely, a normal ACE level does not automatically rule out sarcoidosis, which is an important limitation of the test. The ACE level may not be elevated if the disease is chronic or in a less active phase, or if the granulomas are not producing the enzyme in large amounts.
Therefore, the ACE test is always interpreted in the context of a patient’s overall clinical picture, including physical examination, chest X-rays, and other laboratory work, and is never used in isolation to establish a diagnosis.