When you have granulomas (masses of inflammatory cells) that create small bumps under the skin, a lingering cough, red watery eyes and/or other symptoms suggestive of sarcoidosis. When you have active sarcoidosis in order to follow its progress
A blood sample taken from a vein in your arm
No test preparation is needed
Angiotensin converting enzyme (ACE) is an enzyme which helps regulate blood pressure. It converts angiotensin I (an inactive protein) to angiotensin II which causes arteries to contract, making them temporarily narrower and increasing the pressure of the blood flowing through them. ACE is produced throughout the body, but is present in especially high amounts within the lungs. It is normally found at a high concentration in the bloodstream of those less than 20 years of age, and will usually then drop to lower concentrations in healthy adults.
Increased amounts of ACE are sometimes produced by cells found at the outside borders of granulomas. Granulomas are a classic feature of sarcoidosis, a disorder that often affects the lungs but may also affect many other body organs including the eyes, skin, nerves, liver, and heart. The cause of sarcoidosis is unknown. About 75% of patients with untreated sarcoidosis will have elevated concentrations of ACE in their bloodstream that will rise and fall as the severity of the disease changes. Granulomas, fibrosis, and an elevated ACE concentration may also be seen in infections such as leprosy and tuberculosis. The granulomas form around the invading bacteria in these infections and can also form around irritant particles in poisons such as beryllium, asbestos, and silicon.
How is it used?
Although ACE measurement may not be needed in the diagnosis and monitoring of many patients with sarcoidosis, it can be used to help diagnose and monitor sarcoidosis in some patients. It is often requested as part of an investigation into the cause of a group of long troubling symptoms that may or may not be due to sarcoidosis. ACE will be elevated in around 75% of patients with untreated sarcoidosis. If it is initially elevated in someone with sarcoidosis, ACE can be requested at regular intervals to monitor the course of the disease and the effectiveness of corticosteroid treatment.
When is it requested?
ACE is requested when you have signs or symptoms such as granulomas, a chronic cough or shortness of breath, red watery eyes, and/or joint pain that may be due to sarcoidosis or to another disorder. Sarcoidosis is most commonly seen between 20 and 40 years of age. Your doctor may request ACE with other tests such as X-rays, CT-Scan, tissue biopsies, AFB culture or sputum culture (tests that can detect mycobacterial and fungal infections), to help differentiate between sarcoidosis and another granulomatous condition.
If when you were diagnosed with sarcoidosis, your initial ACE result was elevated, your doctor may request ACE testing at regular intervals to monitor the change in concentration over time.
What does the test result mean?
If someone is under 20 years of age, then high ACE concentrations do not usually indicate disease. For those over 20 years of age, the concentrations of ACE within the blood does not tell you why ACE is elevated, what organs and/or body systems are involved, or how badly they are affected. ACE does not cause granulomas but may reflect their presence.
If ACE concentrations are high, and other diseases have been ruled out and you have clinical symptoms of sarcoidosis, then it is likely that you have active sarcoidosis. About 20-50% of the time, however, sarcoidosis can be present without elevated ACE concentrations. This may be due to the disease being in an inactive state, due to an early detection of sarcoidosis where the levels have not yet risen, or due to the fact that the cells do not produce increased amounts of ACE. An ACE result within the normal (reference) range cannot be used to rule out the possibility of sarcoidosis. ACE concentrations are also less likely to be elevated in those with long term sarcoidosis.
High concentrations of ACE are often observed initially in sarcoidosis, which then decrease with time, which suggests the activity of the disease has decreased without obvious reason or as a result of therapy. Falling concentrations usually indicate a favourable prognosis. Rising concentrations of ACE on the other hand, may indicate either an early disease process that is progressing, or disease activity that is not responding to therapy.
Is there anything else I should know?
ACE conversion of angiotensin I to angiotensin II is a normal regulatory process in the body. This process is targeted by drugs called ACE inhibitors that are commonly used in treating hypertension and diabetes. These drugs inhibit the conversion process, keeping the blood vessels more dilated and the blood pressure lower. ACE inhibitors are useful in managing hypertension but they are not monitored with ACE blood tests.
Haemolysis (broken red blood cells) and hyperlipidaemia (excess fats) in the blood sample may falsely decrease the concentration of ACE within the blood. Decreased ACE concentrations may also be seen in patients with:
- Chronic obstructive pulmonary disease (COPD)
- Cystic fibrosis
- Lung cancer
- Steroid drug therapy
ACE has been found at moderately increased concentrations in a variety of diseases and disorders such as:
- Certain fungal diseases
- Diabetes mellitus
- Alcoholic cirrhosis
- Gaucher disease (a rare inherited lipid metabolism disorder)
The ACE test is not useful in diagnosing or monitoring any of these disorders.
What other tests are used to diagnose sarcoidosis?
A variety of tests may be requested to help diagnose sarcoidosis and to discover the extent of the disease. Laboratory tests may include: liver function tests, full blood count, and calcium. Other tests may include an examination for skin problems, a lung function test (about 90% of the time there will be evidence of lung disease in patients with sarcoidosis), bronchoscopy (passing a flexible tube that is used to look at the lining of the airway and to biopsy the lung), chest x-ray, PET or CT scanning. Biopsies of the skin, lungs, lymph nodes and sometimes liver may also be needed, as may a thorough eye examination (a test called a slit-lamp examination may be used). There is a biomarker (blood test) that appears to perform better than ACE for diagnosing sarcoidosis, soluble interleukin 2 receptor (sIL-2R), however it is not yet routinely available in clinical practice.
What causes sarcoidosis?
The cause is not well understood. It is not easily spread. It is inflammatory and involves the immune system. It appears to have a genetic and environmental association. It is relatively common in Scandinavia and Northern Ireland, but rare in China, Japan, and Africa. For some reason, those who move from a part of the world where the disease is very uncommon to a part of the world where it is common will have a higher risk of developing the disease.
What is the long-term prognosis for sarcoidosis?