ACE (Angiotensin-Converting Enzyme) Test: Purpose, Range & High/Low Causes

What is ACE (Angiotensin-Converting Enzyme)?

ACE, or Angiotensin-Converting Enzyme, is an enzyme that plays a key role in regulating blood pressure and body fluid balance.
Its main job is to convert angiotensin I (an inactive form) into angiotensin II, which is an active substance that narrows blood vessels (vasoconstriction) and increases blood pressure.

The ACE test measures the level of this enzyme in your blood.
It is most often used to help diagnose and monitor sarcoidosis, an inflammatory condition that can affect the lungs, skin, eyes, and other organs.
High or low ACE levels can also point to lung, liver, or thyroid disorders.

Where is ACE Produced in the Body?

ACE is mainly produced in the endothelial cells of the lungs — the cells lining blood vessels.
Smaller amounts are also produced in:

• The kidneys
• The brain
• Other blood vessel tissues throughout the body

This widespread distribution explains why ACE can be found in the bloodstream and can rise in certain diseases.

Main Functions and Importance of ACE

The ACE enzyme is a crucial component of the Renin-Angiotensin-Aldosterone System (RAAS) — the body’s natural system for maintaining blood pressure and fluid balance.

The main roles of ACE include:

1. Converting Angiotensin I → Angiotensin II
   Angiotensin II is a strong vasoconstrictor that narrows blood vessels and raises blood pressure.
2. Stimulating Aldosterone Secretion
   Aldosterone, a hormone produced by the adrenal glands, increases sodium and water retention, which also helps raise blood pressure.
3. Regulating Fluid and Electrolyte Balance
   ACE helps maintain the right volume of fluid and sodium-potassium balance in the body.
4. Supporting Blood Pressure Control
   It plays a major role in long-term regulation of blood pressure.
5. Clinical Marker for Granulomatous Diseases
   Elevated ACE levels are often linked to diseases such as sarcoidosis, tuberculosis, and leprosy, where inflammation forms “granulomas” in tissues.

Causes of Low ACE Levels

Low ACE levels are less common and usually not dangerous by themselves.
They are mostly caused by other underlying conditions or medications.

Common causes include:

• Chronic Obstructive Pulmonary Disease (COPD)
• Emphysema
• Hypothyroidism
• Use of ACE inhibitors (blood pressure medicines such as enalapril, lisinopril, or ramipril)
• Genetic variants that naturally produce less ACE

Symptoms of Low ACE Levels

Low ACE levels usually do not cause direct symptoms, but patients may experience:

• Low blood pressure or dizziness (if related to medication)
• Fatigue and sluggishness (from hypothyroidism)
• Shortness of breath (in lung diseases such as COPD)

Causes of High ACE Levels

High ACE levels are usually seen in diseases that cause inflammation and granuloma formation — small clumps of immune cells that form in tissues.

Common causes of increased ACE include:

• Sarcoidosis (most common cause)
• Tuberculosis (TB)
• Leprosy
• Histoplasmosis (fungal infection)
• Hyperthyroidism
• Lung diseases such as silicosis and asbestosis
• Certain liver disorders

Symptoms of High ACE Levels

ACE itself does not produce symptoms — the symptoms are due to the underlying disease.

Commonly observed symptoms include:

• Persistent cough or shortness of breath (lung involvement)
• Skin rashes or raised lesions (common in sarcoidosis)
• Fatigue and weight loss
• Fever or night sweats (seen in infections such as TB or histoplasmosis)

Reference Range

ACE levels can vary depending on the lab and test method.
Typical reference range in adults:

🧾 Values above 52 U/L may suggest sarcoidosis or another granulomatous condition.

Sample Type and Handling

How the ACE Test is Performed

1. A blood sample is taken from a vein in your arm.
2. The sample is allowed to clot, and serum is separated in the lab.
3. The serum is tested for ACE enzyme activity using biochemical analysis.
4. The results are compared with the reference range to check for abnormalities.

Interpreting ACE Test Results

🔸 ACE levels alone are not diagnostic — doctors use them along with imaging (like chest X-ray or CT) and other tests.

Test Preparation

• No fasting is needed.
• Inform your doctor about any medications, especially ACE inhibitors.
• Avoid heavy exercise or stress before sample collection.
• The test is usually done once diagnosis is suspected and repeated later to monitor treatment response, especially in sarcoidosis.

When to Consult a Doctor

Consult your doctor if you experience:

• Persistent cough or shortness of breath
• Unexplained skin rashes or nodules
• Fever, weight loss, or night sweats
• Fatigue, weakness, or dizziness

These symptoms may indicate underlying lung, liver, or inflammatory conditions that require further evaluation.

Important Word Explanations

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