What Does a Low ACE Level Indicate?

A low serum angiotensin-converting enzyme (ACE) level most commonly reflects one of three things: you are taking a medication that suppresses it, your genetics set your baseline lower than average, or an underlying condition such as hypothyroidism or advanced illness is pulling it down. ACE is an enzyme involved in blood pressure regulation, and doctors sometimes order the blood test when they suspect sarcoidosis or need to monitor certain diseases. But the result often raises more questions than it answers, because so many factors influence the number on the lab slip.

What ACE Does in Your Body

ACE is a key part of the system your body uses to manage blood pressure and fluid balance. It converts a relatively inactive molecule called angiotensin I into angiotensin II, which tightens blood vessels and raises blood pressure. At the same time, ACE breaks down bradykinin, a substance that widens blood vessels and lowers pressure.¹ When serum ACE is measured in a blood test, the result reflects how much of this enzyme is circulating. A level that falls below the lab’s reference range is flagged as “low,” but interpreting that flag requires knowing what is normal for you specifically and what else might be going on.

The Most Common Reason for a Low Result Is Medication

If you are taking an ACE inhibitor for high blood pressure or heart failure, your serum ACE level will almost certainly come back low. This is not a mystery; these drugs work by blocking ACE directly. Yet the test gets ordered for patients on ACE inhibitors more often than you might expect, leading to confusion when the result looks abnormal. A study examining this problem found that ACE levels in patients receiving ACE inhibitor therapy were substantially lower, making the test essentially uninterpretable for diagnosing anything else while you are on the drug.² If your doctor orders a serum ACE test and you are on lisinopril, enalapril, ramipril, or any similar medication, mention it. The result will be meaningless for diagnostic purposes.

Your Genes Set the Baseline

Even before any disease or medication enters the picture, people walk around with very different ACE levels based on their DNA. A well-known genetic variation in the ACE gene, often described as an “insertion/deletion” polymorphism, accounts for roughly half of the total variation in serum ACE from person to person.³ People who carry two copies of the “insertion” variant (the II genotype) tend to have the lowest ACE levels, while those with two copies of the “deletion” variant (DD genotype) tend to have the highest. Heterozygotes fall in between.

The practical spread is significant. In one study of healthy Caucasian volunteers, average serum ACE ranged from about 25 to 44 units per liter depending on genotype and assay method, while the DD group averaged 44 to 59 units per liter.⁴ A similar pattern appeared in a Saudi Arabian cohort, where healthy II-genotype individuals averaged about 21 units per liter and DD individuals averaged about 41.⁵ This means a person with the II genotype whose level sits near the bottom of a standard reference range is perfectly healthy. Their ACE is low for the population but normal for their genotype.

Researchers have argued that labs should adopt genotype-specific reference ranges, especially when using the ACE test to monitor sarcoidosis, because a one-size-fits-all cutoff misclassifies a lot of people.⁴ Most labs have not made the switch, so if your result looks low, your genetics could easily be the explanation.

Hypothyroidism and Low ACE

An underactive thyroid gland tends to drag serum ACE levels down. In a study comparing euthyroid subjects (normal thyroid function) with hypothyroid patients, the average ACE level in the hypothyroid group was noticeably lower. When twelve of those hypothyroid patients were treated with thyroid hormone replacement, their ACE levels climbed back up.⁶ A separate study looking at patients with primary hypothyroidism found a similar trend, with ACE activity averaging around 10 units per liter compared with higher values in healthy controls.⁷

The takeaway here is straightforward: if you have untreated or undertreated hypothyroidism, a low ACE result could be reflecting your thyroid status rather than anything else. Your doctor may need to know your thyroid function before drawing conclusions from the ACE number.

Corticosteroids Push ACE Down

Steroid medications like prednisone directly suppress serum ACE. This effect is well documented in sarcoidosis patients, where corticosteroids are a frontline treatment, but it happens in people without sarcoidosis too. In one study, patients who started on prednisone and had ACE levels in the normal-to-high range saw a significant drop within a week. Those whose levels were already low before treatment did not drop further, since there was not much room to fall.⁸

A separate analysis of sarcoidosis patients found a strong inverse relationship between steroid dose and ACE level: when the dose went up, ACE came down, and vice versa.⁹ If you are on prednisone, dexamethasone, or another corticosteroid for any reason, your ACE level will reflect that treatment. Clinicians monitoring sarcoidosis with serial ACE measurements need to factor in any dose changes when interpreting the trend.

Low ACE in the Context of Sarcoidosis Monitoring

Most people encounter the ACE blood test because sarcoidosis is suspected or already diagnosed. In sarcoidosis, ACE tends to run high because granulomas (clusters of immune cells) produce extra ACE. A falling or normal ACE level in a sarcoidosis patient usually signals that the disease is responding to treatment. After therapy with immunosuppressive drugs, serum ACE levels have been observed to drop back to normal as the condition improves, and then rise again if the disease flares.¹⁰

But the test has real limitations even in this context. A recent single-center study found that elevated ACE had a sensitivity of only about 64% and a specificity of about 60% for diagnosing sarcoidosis. The negative predictive value was high, around 95%, meaning a normal or low ACE makes sarcoidosis somewhat less likely, but a low result alone cannot rule it out or confirm it.¹¹ Many other conditions also influence the number, and the same study noted that ACE inhibitor use, lymphoma, cirrhosis, and interstitial lung disease all affected ACE levels in their cohort. For sarcoidosis, ACE is best understood as one data point among many rather than a definitive marker.

Lung Cancer and Other Malignancies

Low ACE levels have been documented in patients with certain cancers, particularly primary lung cancer. In a study of nearly 200 cancer patients, most presented with normal-to-low ACE levels, averaging about 70% of the standard value. Patients with primary lung cancer were significantly more likely to have low readings than patients with cancers elsewhere in the body.¹² A separate study of 141 patients with newly diagnosed lung cancer found their mean serum ACE was lower than that of healthy controls.¹³

The mechanism is not entirely clear, but one hypothesis involves damage to the pulmonary vascular endothelium, where a large share of ACE is normally produced. Lung tumors may disrupt or replace that tissue, reducing the body’s overall ACE output. This finding does not mean that a low ACE result should make you worry about cancer. The test is not used as a cancer screening tool, and a low result has many far more common explanations. But in someone already being evaluated for lung disease, the ACE level can contribute to the clinical picture.

Age Matters More Than You Might Expect

Children naturally have higher serum ACE levels than adults. Studies have confirmed that ACE activity in children is significantly higher than in adults and that levels decrease as children move into adolescence.¹⁴ A detailed study of 187 healthy children aged six months to 18 years found that the decline was age-related starting around age four, and that adolescent boys had higher levels than adolescent girls, possibly due to hormonal influences on ACE production.¹⁵

For a practical standpoint, this means adult reference ranges should not be applied to children, and a result that would be flagged as “normal” in an adult might actually be low for a child. Labs that do not use pediatric-specific reference ranges risk misinterpreting results in younger patients.

Reference Ranges Vary Between Labs

There is no single universally agreed-upon cutoff for “low” ACE. One commonly cited adult reference range runs from 8 to 65 units per liter for people over 14.¹⁶ But different assays yield different numbers, which is part of why the genotype-corrected approach mentioned earlier has been proposed. Two commonly used kinetic assays tested on the same population of healthy subjects produced noticeably different absolute values, even though the rank order across genotypes stayed the same.⁴ If your result is close to the lower boundary of your lab’s range, it is worth knowing that another lab using a different assay might report you as solidly within normal.

Lab Handling Can Affect the Number

Hemolysis, the breaking apart of red blood cells in a blood sample, can slightly suppress ACE readings. One study characterizing an optimized ACE assay noted that hemoglobin concentrations above a certain threshold caused a slight negative interference with the measurement.¹⁷ More recent research has explored this further, finding that hemolyzed plasma showed reduced ACE activity even though ACE protein levels were unchanged, suggesting that substances released from ruptured red blood cells inhibit ACE function in the test tube.¹⁸ A rough blood draw, poor sample handling, or delayed processing can cause enough hemolysis to nudge the result lower. If your result is unexpectedly low and the sample was flagged as hemolyzed, a redraw may be warranted.

Kidney Disease and ACE Levels

The relationship between kidney disease and serum ACE is complicated and somewhat inconsistent across studies. Early research on patients with end-stage kidney disease on chronic hemodialysis found that their ACE levels were below the normal mean, and that starting hemodialysis brought levels closer to normal over time.¹⁹ However, later work painted a more complex picture. A study of hemodialysis patients with cardiovascular disease found that their plasma ACE was actually elevated compared with healthy controls, and it rose further during a single dialysis session.²⁰

Part of the confusion may stem from the toxic environment of uremia. Research using detailed “ACE phenotyping” found that some patients with end-stage kidney disease showed structural changes in their circulating ACE protein, possibly caused by uremic toxins.²¹ The upshot is that serum ACE in kidney disease is not reliably low or reliably high. The direction may depend on the specific stage of disease, whether cardiovascular complications are present, what medications the patient is on, and even how the sample is handled relative to a dialysis session. A low ACE level in someone with chronic kidney disease should not be over-interpreted without additional context.

When a Low ACE Level Actually Matters

In most clinical scenarios, a low ACE level is either explained by something obvious (medication, genetics, thyroid status) or is simply uninformative. The test was originally popularized as a diagnostic tool for sarcoidosis, and even there its track record is modest. Outside of sarcoidosis monitoring, very few clinical decisions hinge on a low ACE result. Your doctor is unlikely to order follow-up testing based solely on a low number unless there are other clinical findings pointing toward a specific condition.

Where a low result can be genuinely useful is in the serial monitoring of a known condition. If you have been diagnosed with sarcoidosis and your ACE level drops to normal during treatment, that is a favorable signal, though it is not proof of remission on its own.¹⁰ If a previously elevated level suddenly falls and you have not started a new medication, it is worth investigating whether treatment is working or another factor has entered the picture. But a single low reading in a person who has never had a prior ACE measurement provides very little actionable information.

Conditions That Raise ACE, and Why That Context Helps

Understanding what pushes ACE up helps frame what “low” actually means. The multivariate analysis from a large retrospective cohort identified sarcoidosis, non-Hodgkin lymphoma, cirrhosis, interstitial lung disease, and not taking ACE inhibitors as factors that significantly increased the odds of an elevated reading.¹¹ Liver fibrosis from chronic hepatitis B has also been associated with higher ACE as the scarring progresses.²²

If none of those conditions apply to you, and you are not on an ACE-raising medication like thyroid hormone at a supraphysiologic dose, then a low ACE level is probably just your personal normal. Many people with the II genotype at the ACE gene locus will sit at the bottom of the reference range for their entire lives without any health consequence. The enzyme’s circulating level, unlike something like blood glucose, does not have a well-defined “too low” threshold that maps onto a clinical syndrome. Your body can regulate blood pressure through other pathways and feedback loops even when circulating ACE is on the lower end. The test is a diagnostic aid for specific conditions, not a standalone health marker.

1
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2
PubMed. Ordering of the Serum Angiotensin-Converting Enzyme Test in Patients Receiving Angiotensin-Converting Enzyme Inhibitor Therapy: An Avoidable but Common Error
3
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4
PubMed. Genotype-corrected reference values for serum angiotensin-converting enzyme
5
PubMed Central. ACE insertion/deletion genetic polymorphism, serum ACE levels and high dietary salt intake influence the risk of obesity development among the Saudi adult population
6
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8
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10
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11
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12
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13
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14
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15
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PubMed Central. Serum Level of the Angiotensin-Converting Enzyme in Patients with Idiopathic Acute Optic Neuritis: A Case-Control Study – Section: Materials and Methods
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PubMed Central. Severe Acute Hypertension Causes Hemolysis With Release of PEP and ACE Inhibitor
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PubMed. Angiotensin-converting enzyme activity in renal disorders: influence of disease pattern, hemodialysis and transplantation
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PubMed Central. Imbalanced plasma ACE and ACE2 level in the uremic patients with cardiovascular diseases and its change during a single hemodialysis session
21
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PubMed Central. Serum angiotensin-converting enzyme level for evaluating significant fibrosis in chronic hepatitis B