What is Acetylcholine (Ach)?
It is an organic chemical (neurotransmitter) of parasympathetic nervous system, which is involved in contraction of smooth muscle, dilates blood vessels, slows heart rate & increases bodily secretions. It is made by the enzyme choline acetyltransferase & then transported into synaptic vesicles where they get attached to specific receptors and produce action in body.
What is ACRA lab test?
Acetylcholine receptor antibodies (also abbreviated AChR) are autoantibodies (antibodies that mistakenly target/react with a person's own tissues) which are produced by immune system. They mistake body’s own proteins called acetylcholine receptors located on muscles as foreign antigens and start targeting them. The acetylcholine which initiates muscle contraction when it reaches muscle fiber and gets attached to the acetylcholine receptors is deactivated by the release of AChR antibodies. These antibodies prevent activation of acetylcholine receptors and impede communication b/w nerves & skeletal muscles, inhibit muscle contraction & cause rapid muscle fatigue. Which eventually leads to an autoimmune disorder called myasthenia gravis. This lab test basically detects & measures the presence of AChR antibodies in blood.
Why is ACRA lab test done?
During this test, three types of AChR antibodies can be tested namely AChR binding antibodies (most used), AChR blocking antibodies, and AChR modulating antibodies. The test is done:
- To help diagnose myasthenia gravis (MG)
- To distinguish it from other muscle conditions having similar symptoms as MG.
- If thymoma (benign thymus tumor) detected, then MG is suspected as well, for which this test can help measure the presence of antibodies.
- How long will it take for AChR test?
Its results may come within 7 to 10 days.
- Acetylcholine receptor antibodies are found in which disorder?
Most common primary disorder affecting neuromuscular transmission is myasthenia gravis, therefore, in 80% to 90% patients AChR antibodies can be detected. Also detected in 50% patients with pure ocular myasthenia & rarely found in healthy people.
- What happens if acetylcholine is released in excess?
It leads to muscarinic & nicotinic toxicity whose symptoms include cramps, increased salivation, muscular weakness, lacrimation (flow of tears), paralysis, diarrhea, & blurry vision
- Which diseases are associated with acetylcholine imbalance?
An imbalance in acetylcholine concentrations leads to chronic diseases like Parkinson’s & Alzheimer’s disease.
- How can MG be diagnosed?
The most important test known for MG is blood test that looks for type of antibody released by immune system which stops signals sent b/w nerves & muscles (AChR antibodies).
INTERPRETATION OF THE RESULTS:
- Normal Results: there is normally no AChR antibody present in the bloodstream or can be in less than 0.05 nmol/L concentration.
- Abnormal Results: It simply means that AChR antibody has been found in the blood & it confirms the diagnosis of myasthenia gravis. Its results can be considered positive in this manner:
- Weak positive: 0.5 to 1.0 nmol/L
- Positive: 1.0 to 5.0 nmol/L
- Strong positive: >5.0 nmol/L
The test helps in diagnosing myasthenia gravis (autoimmune disorder) & distinguishes it from other muscle conditions.