Thermoregulatory sweat test (TST)

The TST is a clinical test that is used to aid diagnosis of disorders related to thermoregulation and sweat production abnormalities in the body. The test measures a patient’s ability to produce sweat in a temperature-controlled environment and assists the consultant in diagnosing medical conditions or planning and carrying out treatments.

A TST is a useful diagnostic test, although any clinical benefit should always outweigh the possible risks associated with the procedure.

Common concerns from patients in relation to the heating chamber include overheating and claustrophobia during testing. If at any point during the test you become too uncomfortable and wish to terminate the test, then you should inform the clinical autonomic scientist (CAS) who is performing the test.

The TST involves the use of a powdered dye which will be sprinkled over your whole body, including your face. The powder contains the food additive, Allura Red, which has been shown to be safe for consumption at the levels which would occur during a TST [1]. In the unlikely event that you notice an allergic reaction to the powder during testing, you should inform the CAS in the first instance.

It is not uncommon to feel slightly light-headed or dizzy following the test due to the heat and humidity of the chamber fluids will be available if needed, although it is recommended that you bring your own bottle of water.

The decision to have a TST is entirely yours. Declining this procedure will not affect our attitude towards you or influence any other aspect of your care. It may mean, however, that your consultant cannot be as certain or specific about any future treatment or diagnosis.

Your consultant or clinical nurse specialist (CNS) will have taken into account the potential risks and benefits of having a TST during your initial referral. There are some alternative methods which may be available under certain circumstances, although the possibility of these should be discussed with your referring doctor or CNS.

Please do not eat four hours prior to testing; you may drink water only - if possible, please drink approximately 500 ml of water (a small bottle) one to two hours before testing. It is advisable to bring with you a bottle of water to help re-hydrate after testing.

If you are not able to lie still on your back for prolonged periods, please inform us by telephone.

Should you prefer to wear your own underpants for testing as opposed to the disposable ones that we can provide, we recommend that you wear old ones in case of any staining from the powdered dye.

For those with long hair, you should tie it up away from your face and neck. Please bring a shower gel/shampoo and clean underpants (if choosing to wear your own during heating) with you.

Do not wear make-up or deodorant or moisturiser. Please remove any fake tan.

You may need to stop certain medications prior to testing, although the consultant or CNS should be able to advise you during your initial consultation; if you are unsure, please call us directly or ask us when you confirm your appointment.

We want to involve you in all the decisions about your care and treatment. If you decide to go ahead with treatment, by law we must ask for your consent. This confirms that you agree to have the procedure and understand what it involves, which includes the taking of digital photographs throughout testing; only those persons involved in your care will be able to view the photographs.

If you are unsure about any aspect of your proposed treatment, please do not hesitate to speak with a senior member of staff again.

The TST suite encompasses:

• a washroom facility – includes a shower, sink and toilet, and a place to protect your privacy whilst changing (the clinical autonomic scientist performing the test will usually be the same gender as you)
• an ante-chamber – where preparation for heating and monitoring take place
• the TST chamber – where the heating process takes place. The facility is fitted with an intercom that will allow communication with the CAS during heating. Testing, which includes preparation, heating and post-heating procedure, will take approximately two and a half hours.

The TST suite:

The testing procedure

You will be asked to lie down (on your back) on a trolley wearing only underpants (either your own or disposable ones that can be provided) and then placed into the heated TST chamber on the trolley whilst lying on your back for a maximum of 60 minutes.

Prior to entry into the TST chamber (whilst lying on your back on the trolley) you will be fitted with:

• an in-ear temperature sensor that fits snugly into your preferred ear (your in-ear temperature will be monitored continuously throughout heating)
• skin sensors (taped to the skin in various locations) that will monitor skin temperature

Powdered dye will then be sprinkled over your whole body, including your face (glasses will be provided to protect your eyes); the dye will turn from pink to bright red when in contact with moisture (i.e., sweat) to accurately show the areas of sweating. The dye will wash off in the shower before you leave.

Digital photographs will be taken at the beginning of heating, during and at the end; we will have to obtain your consent prior to doing so. Only those persons involved in your care will be able to view the photographs.

Once the heating process is complete and all relevant photographs have been obtained, you will be removed from the chamber.

As soon as the test is complete, you will then be able to have a shower in our washroom facility to wash off the powdered dye.

Once you have completed all of your clinical tests with us, the results will be analysed and discussed at a multi-disciplinary team (MDT) meeting.

A brief summary letter will then be sent to you and your referring doctor (normally your GP) detailing the results of your tests.

You will then have a follow-up appointment with a consultant or a CNS to explain the results in more detail, and to also answer any questions you may have.

[1] Scientific Opinion on the re-evaluation of Allura Red AC (E 129) as a food additive on request from the European Commission. EFSA Journal 2009; 7(11):1327.

National Hospital of Neurology and Neurosurgery
The Autonomic Unit (Box 87)
2nd Floor Queen Mary Wing
Queen Square
London WC1N 3BG

Direct tel: 0203 448 3709
Switchboard: 0203 456 7890
Fax: 0203 448 3878
Email: uclh.enquiry.autonomic.secretaries@nhs.net

The Autonomic Unit is located on the second floor of the Queen Mary Wing at the National Hospital for Neurology and Neurosurgery, Queen Square. Please follow signs from the main entrance towards the Queen Mary Wing and you should find the appropriate set of lifts/stairs on your right-hand side. Head to the second floor and use the intercom to contact our admin team who will let you in once you have confirmed your identity.