An angiotensin converting enzyme (ACE) blood test measures the level of ACE in your blood, primarily to help diagnose or monitor sarcoidosis, a condition where clusters of inflammatory cells form in organs like the lungs, skin, and eyes. For adults, a normal ACE level is generally less than 40 micrograms per liter, though exact ranges vary by lab and testing method.
What ACE Does in the Body
ACE is an enzyme your body produces mainly in the lungs, though it’s also made by cells in the brain, liver, pancreas, and immune system. Its best-known job is regulating blood pressure: it converts one hormone into another that tightens blood vessels and signals your kidneys to retain sodium and water. This is the same system that ACE inhibitor medications (commonly prescribed for high blood pressure) are designed to block.
The reason ACE levels matter in a blood test has little to do with blood pressure, though. When certain diseases cause your immune system to form granulomas (small clusters of inflamed tissue), the cells in those granulomas produce extra ACE and release it into the bloodstream. A spike in ACE levels can signal that this process is happening somewhere in the body.
Why Your Doctor Ordered This Test
The most common reason for an ACE blood test is suspected sarcoidosis. Sarcoidosis can affect the lungs, heart, eyes, skin, and nervous system, but it’s notoriously difficult to pin down because symptoms develop slowly and can mimic many other conditions. ACE serves as the most commonly used blood marker for sarcoidosis because the granulomas themselves are churning out the enzyme. More than 75% of untreated sarcoidosis patients have elevated ACE levels.
Beyond initial diagnosis, the test is also used to track how well treatment is working. ACE levels typically drop back to normal as the disease responds to therapy and rise again if sarcoidosis flares. Monitoring the trend over time gives a picture of disease activity without repeated imaging or biopsies.
Less commonly, the test may be ordered when a doctor suspects other granulomatous conditions like tuberculosis or certain fungal infections, or when evaluating unexplained lung symptoms alongside imaging and other bloodwork.
How Accurate the Test Is
The ACE test is better at ruling sarcoidosis out than confirming it. In a large population-based study, its sensitivity was only about 41%, meaning it misses more than half of sarcoidosis cases. Its specificity was roughly 90%, so about 1 in 10 people without sarcoidosis will still test falsely high. When ACE is more than double the upper limit of normal, the result becomes much more specific to sarcoidosis.
Because of these limitations, a high ACE level alone is never enough to diagnose sarcoidosis. Doctors combine it with chest imaging, sometimes a tissue biopsy, and a careful review of symptoms. Think of the ACE test as one piece of a puzzle rather than a standalone answer. Where the test shines is in tracking disease over time: serial measurements showing a clear upward or downward trend are more informative than any single reading.
What High ACE Levels Can Mean
Sarcoidosis is the condition most closely linked to elevated ACE, but it is not the only one. Other conditions associated with high ACE include:
- Gaucher’s disease, a rare inherited metabolic disorder
- Hyperthyroidism
- Tuberculosis and histoplasmosis (granulomatous infections)
- Hodgkin’s and non-Hodgkin’s lymphoma
- Cirrhosis of the liver
- Silicosis and asbestosis (occupational lung diseases)
- Diabetes
This long list is part of why a single elevated result can’t point to one diagnosis. Your doctor will interpret the number alongside your symptoms, imaging, and other lab work.
What Low ACE Levels Can Mean
Abnormally low or undetectable ACE almost always has a straightforward explanation: you’re taking an ACE inhibitor for blood pressure. Medications like lisinopril, enalapril, and captopril work by suppressing ACE activity, so they drive blood levels down to extremely low or unmeasurable levels. This is a surprisingly common testing error. If you’re on an ACE inhibitor and your doctor orders this test, the result will be artificially low and essentially uninterpretable for diagnosing sarcoidosis or anything else.
If you aren’t taking any blood pressure medication and your result comes back low, it generally falls within the normal range and isn’t a cause for concern on its own.
How the Test Works
The ACE test is a standard blood draw from a vein in your arm. No special fasting is required. The sample is sent to a lab, where enzyme activity is measured. Results are typically reported in units per liter, with normal adult values falling below 40 micrograms per liter, though the exact cutoff depends on your lab’s method and reference range.
One important thing to keep in mind: normal ranges also vary by age. Children and teenagers tend to have higher ACE levels than adults, so a result that looks elevated for a 50-year-old might be perfectly normal for a 15-year-old. Your lab report should include the specific reference range used.
Medications That Affect Results
If you take an ACE inhibitor for blood pressure or heart failure, mention it before this test is ordered. ACE inhibitors suppress the very enzyme being measured, making the test unreliable. In one study examining this issue, a notable proportion of ACE tests were ordered on patients already taking these medications, representing a common and avoidable error that wastes time and money.
Other classes of blood pressure medication, like ARBs (angiotensin receptor blockers), work differently and do not suppress ACE enzyme levels the same way. Still, let your doctor know about all medications you take so the result can be interpreted correctly.
What Happens After the Test
If your ACE level comes back normal and your doctor had a low suspicion of sarcoidosis, no further testing may be needed. If the level is elevated, expect additional workup. For suspected sarcoidosis, that typically means a chest X-ray or CT scan looking for enlarged lymph nodes and lung involvement, and possibly a biopsy of affected tissue to confirm granulomas under a microscope.
If you’ve already been diagnosed with sarcoidosis and this test is part of ongoing monitoring, your doctor is looking at the trend. A falling ACE level suggests the disease is responding to treatment. A rising level, especially after medication has been reduced or stopped, can signal a relapse. These serial measurements help guide decisions about whether to continue, adjust, or restart therapy.