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What is the Scleroderma Antibody (Scl-70) test?

The scleroderma antibody (Scl-70) test works by detecting the presence of scleroderma antibodies in the serum. Scl-70 antibodies are also referred to as topoisomerase antibodies. Topoisomerases are a group of nuclear enzymes that generally work to loosen double-stranded DNA so that the DNA can replicate. Scl-70 antibodies are the antibodies produced by our immune system to oppose various topoisomerases, so their function is hindered, resulting in a group of diseases, which in clinical medicine is known as scleroderma but is better named as systemic sclerosis. These antibodies affect the skin, but the gastrointestinal tract, kidneys, heart, muscles, lungs, and blood vessels are frequently involved.

Scleroderma may be limited or diffused depending upon the area of skin involved;

Diffused scleroderma is characterized by early widespread skin involvement, with rapid progression and visceral involvement, while in limited scleroderma, the skin involvement is confined to fingers, forearms, and face.

What is this test used for?

This test detects scleroderma (Scl-70) antibodies in the blood, confirming the patient’s diagnosis of systemic sclerosis. About 40% of the patients with systemic sclerosis test positive for the Scl-70 antibodies. Scl-70 antibodies are specifically present in a patient’s blood with a diffused type of systemic sclerosis. These antibodies are not necessarily present in all patients with systemic sclerosis, but their presence tells the severity of the disease. Moreover, lower levels of these antibodies can also be found in some patients with SLE (systemic lupus erythematosus). Besides that, patients containing these antibodies have a high frequency of getting lung fibrosis.

Why and when do you need a Scleroderma Antibody (Scl-70) test?

Your doctor may order a Scleroderma antibody (Scl-70) test if you have been suspected of having the diffuse type of systemic sclerosis, which is presented by;

Joint pain may be caused by stretching the skin over the joints. It may also be caused by inflammation and hyperplasia of the synovium.
Tightened or hardened skin is caused by overstimulation of fibroblasts which produce more collagen. Hardening is first seen in the skin of the fingers and then progresses proximally to affect the forearm, arm, and face. The skin then feels hard to touch and itchy.

Gastrointestinal tract dysfunction occurs, including mal-absorption of nutrients due to villi and microvilli loss. It also presents inflexibility of the lower part of the esophagus due to excess collagen deposition, which causes esophageal reflux and can lead to complications like barrett-esophagus. The patient can have signs like difficulty swallowing, vomiting, or diarrhea.

Raynaud’s phenomenon is presented with swollen hands and toes. It occurs due to episodic vasoconstriction of the blood vessels, and the skin turns red, blue, or numb in response to cold.

What kind of sample is required?

Usually, rheumatologists use a blood sample to find Scl-70 antibodies. A healthcare professional will find a suitable vein on your arm to take a blood sample, rub the area with an antiseptic to avoid any infection, and gently push the needle into the vein. The blood will be drawn out and stored in the tube attached to the needle and sent to the laboratory to check for the presence of Scl-70 antibodies. An indirect immunofluorescence assay (IFA) is recommended to obtain accurate results.

Do you need to prepare for the test?

No special preparations or fasting are needed before taking the Scleroderma antibody (Scl-70) test. Still, you should talk to your doctor if you take any medicines to alter your test results.

Are there any risks to this test?

Because it is a blood test, it has none to low risks. You may feel the needle prick with a bit of bleeding during the test and get some bruising later, which is normal. You should be concerned and consult your doctor if you experience symptoms like;

  • Infection at the pierced skin.
  • Excess bleeding.
  • Blood accumulation under the skin (hematoma).
  • Fainting.

What does the test result mean?

Remember that your doctor must always be the one concluding your diagnosis by examining your symptoms and test results. But if you have anti-Scl-70 antibodies in your blood, they are a specific marker of the diffused type of systemic sclerosis. That means your immune system is making autoantibodies against your DNA topoisomerases, and other than the cutaneous conditions following complications can occur.  

1. Pulmonary-cardiac difficulties:

Pulmonary fibrosis causes respiratory problems, which may result in right-sided cardiac dysfunction, which in turn causes cardiac arrhythmias and cardiac failure. Thus, pulmonary fibrosis has become the primary cause of death in systemic sclerosis.

2. Gastrointestinal tract abnormalities:

Here, esophageal fibrosis gives rise to dysphagia (difficulty swallowing) and the dilation of the lower end of the esophagus, causing abdominal pain and intestinal obstruction. Nutritional deficiencies also result due to mal-absorption.

3. Renal dysfunction:

Some cases of systemic sclerosis are also accompanied by proteinuria, which causes nephrotic syndrome and malignant hypertension. These conditions eventually result in renal failure.

Related tests:

  • Antinuclear antibodies (ANA).
  • Anti-centromere antibodies (ACA).
  • Anti-histone antibodies (AHA).
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