Do you sometimes sweat a lot for no reason, or do you feel like you're sweating less in some places? Or do you have minor things like numbness in your legs or dizziness? Sometimes it can be difficult for a doctor to immediately find the cause of these symptoms. At such times, a special test may be suggested to see if there is a problem with the nervous system that we work unconsciously in our body (the part that controls things like breathing and sweating). This is one such test called QSART.
Simply put, what is QSART?
QSART stands for 'Quantitative Sudomotor Axon Reflex Test'. While the name may sound complicated, it's actually quite simple. Simply put, it's a test that measures how well the nerves that control your sweating are working. We also call it a 'sweat test'.
Think about it, sweating is very important for controlling our body temperature. This sweating is controlled by a special part of our nervous system. In this test, we apply a very small electrical stimulation to a small area of your skin and measure how much sweat your sweat glands produce in response. By measuring the amount of sweat produced in this way, we can get a good idea of the function of the nerves involved.
In what cases would a doctor recommend this test?
This QSART test is very helpful in diagnosing diseases of the Autonomic Nervous System, which controls the functions of our body that we do not consciously control (for example, heart rate, blood pressure, sweating, digestion). It is also used to diagnose peripheral neuropathies, which are related to things like numbness in the limbs, and some pain conditions.
Your doctor may suggest this test if he or she suspects you have one of the following conditions:
- Autonomic neuropathy: Damage to the nerves that control automatic functions in our body.
- Complex regional pain syndrome (CRPS): Severe, long-lasting pain in an arm or leg, usually after an accident.
- Diabetes-related neuropathy: Nerve damage caused by diabetes.
- Multiple sclerosis: A disease that damages the nerves in the brain and spinal cord.
- Postural orthostatic tachycardia syndrome (POTS): A condition in which the heart rate increases abnormally when standing.
- Sjögren's syndrome: An immune system disease that affects the glands that produce moisture in the body (tears, saliva).
- Small fiber neuropathy: Symptoms such as pain and numbness occur due to damage to the small nerve fibers in the skin and organs.
How should I prepare for this test?
Before the QSART test, your doctor will talk to you and explain everything. He or she will also give you some special instructions to follow to ensure accurate test results. It is very important that you follow these instructions exactly.
Let's look at the table below to see how we should generally prepare.
| Instruction | Description and Reason |
|---|---|
| Some medications | You may be asked to stop taking certain medications for a day or two that can affect the test results. Your doctor will tell you exactly what they are. Never stop taking any medication without first asking your doctor. |
| Tobacco products | Avoid smoking and using other tobacco products for at least four hours before the test. These can affect the nervous system. |
| Clothing | Wear loose, comfortable clothing on the day of the test. Do not wear tight-fitting socks (compression stockings) on the day of the test. |
| Lotions and creams | The morning of the test, do not apply any lotions, creams, or oils to your hands and feet. These can interfere with the test equipment from contacting the skin. |
| Food and drink | There are some special instructions for this, which we will discuss separately below. |
Things you need to know about eating and drinking before the test
| What to Do | Time Frame |
|---|---|
| Do not drink anything containing alcohol. | From 12 hours before the test. |
| Do not consume anything that contains caffeine (tea, coffee, chocolate, some soft drinks). | From 8 hours before the test. |
| Eat a light meal (e.g. some rice, a slice of bread) | 3 hours before the test. |
| Avoid drinking anything (even water). | From 3 hours before the test. |
| Drink plenty of water and stay hydrated. | The day before the test. |
What medications may need to be stopped before the test?
Most importantly: Don't stop taking any medication until your doctor tells you to. Some medications can cause other problems if you stop taking them. So, tell your doctor about all the medications you're taking (including vitamins and herbal remedies). He or she will tell you if you need to stop taking any and how soon.
Below are some medications that can commonly affect QSART results. Your doctor may ask you to stop taking some of these for 48 hours before the test.
- Analgesics
- Antidepressants
- Antihistamines (medicines for allergies)
- Anti-inflammatory agents
- Aspirin
- Blood pressure medications
- Diuretics
- Over-the-counter cold or cough medications
Okay, now let's see what happens when we do the test.
Knowing in advance how the test will be done can help reduce anxiety. It's a very simple process.
1. Preparation: First, you will be asked to take off your shoes and socks. Then, you will be asked to sit on an examination table or lie down.
2. Skin cleansing: The examiner will thoroughly cleanse and dry the skin around your legs, feet, and wrists.
3. Attaching the electrodes: Next, four small plastic patches called electrodes are attached to your skin. Usually, three are attached to your legs and one to your wrists.
4. Applying a special solution: Next, a solution called `acetylcholine` is applied to the skin where the electrodes are. `acetylcholine` is a chemical (neurotransmitter) that is naturally present in our body and carries messages between nerves. Here, it is used to stimulate your sweat glands.
5. Starting the test: Now the QSART machine is turned on. Then a very, very small electric current is sent to your skin through the electrodes. This is not a large current, so there is nothing to be afraid of.
6. Sweat measurement: This electric current and the `acetylcholine` solution cause your sweat glands to start producing sweat. The machine measures the amount of sweat produced.
7. Repeat: The officer may remove the electrodes and attach them to other parts of the body, repeating the process.
How long does this test take? Does it hurt?
The entire test usually takes about 45 minutes to an hour .
This is not a painful test. However, some people may feel a little discomfort. When the small electrical current passes through the skin, it may feel like a tickle, a small tingle, or a slight burning sensation, like a tiny needle prick . This varies from person to person. However, it is not unbearable pain. If you feel a lot of pain, tell the person doing the test right away.
What happens after the test? When will the results be available?
After the test is over, the officer will remove the electrodes from your skin. After that, you can put on your socks and shoes again and live normally.
You may notice a slight redness or discoloration of the skin where the electrodes were placed. This is normal and will disappear completely within a few hours.
The data obtained from the test will be sent to the doctor who referred you for this test. He or she will contact you in a few days when the results are available.
How to understand QSART results?
Your doctor will analyze the results and explain their meaning to you. When looking at these results, there are three main things to look for:
- Onset latency: How long did it take for sweating to occur after the stimulus?
- Peak sweat production: When is the greatest amount of sweat produced?
- Total sweat volume: How much sweat was produced during the entire test period?
These results can be 'Normal' or 'Abnormal'.
What is a normal result?
If the result is 'Normal' (sometimes called a 'negative result'), it means that the amount and duration of your sweat production are within the expected range for your age and gender. This means that the test does not indicate a major problem with the functioning of the nerves that control sweating.
What is an Abnormal / Positive result?
If the result is 'Positive' or abnormal, it means that the test values are different from what is expected. For example, it may take a long time to start sweating, or the amount of sweat produced may be too little or too much.
This suggests that something may be interfering with the functioning of your autonomic nervous system.
The important thing to understand here is that a 'positive' QSART test result does not directly mean that you have a disease. It means that something is not working properly in your autonomic nervous system and that further investigation is needed. It is only an important clue that the doctor will get to diagnose your condition. He or she can then decide whether to do further tests or start treatment that is right for you.
Take-Home Message
- QSART is a safe and painless test that measures the activity of the nerves that control your sweating.
- To obtain accurate results, it is essential to strictly follow the diet, medication, and other instructions given by the doctor before the test.
- Tell your doctor about all the medications you are taking. Avoid stopping any medication without your doctor's advice.
- The discomfort felt during the test is usually a tingling or mild burning sensation. It is not unbearable pain.
- A 'positive' (abnormal) test result is not a diagnosis. It is just important information that helps your doctor investigate your condition further.
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