Testing for MH
It is really important that anyone who has suspected MH undergoes testing. This is because it could be a life-threatening condition for a patient’s relatives as well as themselves. The more we research and learn about existing MH patients, the more likely we will help future sufferers.
There are two types of test to confirm MH. These are:
- Genetic screening (blood test)
- Muscle biopsy
Your GP, or consultant, will be able to advise you on the most appropriate type of screening for your particular case after corresponding with the specialist unit in Leeds.
Genetic screening
Genetic screening via a blood test may be offered as the initial test to a person who has had a suspected MH reaction. If a gene change known to cause MH is found in the blood sample then MH will be confirmed, and no further testing will be needed. However, a large number of MH patients (c. 60-65%) do not necessarily have an identifiable gene change and would need to undergo further testing using the muscle biopsy. Where a gene change is found in the family, genetic screening can initially be used in other family members.
In those cases who are put forward for genetic screening, a blood test will be taken at a local GP practice and sent off to for screening at the specialist UK MH investigation centre in Leeds.
Muscle biopsy
Muscle biopsy testing for MH involves a two-night stay at the Leeds MH Investigation Unit at St James’s Hospital in Leeds.
- Download our factsheet on Muscle Biopsy testing here.
What does the test involve?
A sample of muscle tissue is taken through an incision in the lower thigh (c. 2-2.5 inches). The procedure is done under local anaesthetic and takes 30 to 40 minutes to be done.
The muscle biopsy must be done in Leeds because the samples need to be processed and taken to the laboratory within 15 minutes of their removal from the leg.
What happens once the sample is taken?
Muscle samples are kept in a way that mimics the environment within the body as closely as possible. In the specialised MH laboratory the samples are put in a tissue chamber where muscle contraction can be measured. Once stabilised in the tissue chamber the principal test involves exposing the muscle to halothane, one of the triggering anaesthetics. Halothane causes normal muscle to relax but in MH muscle halothane causes a spasm or contracture to develop.
A second test involves exposing separate pieces of muscle to caffeine, the chemical found in coffee, tea and cola drinks. However, the concentrations of caffeine used in MH tests are much higher than can be tolerated by the human body. These concentrations of caffeine can be used to distinguish normal muscle from MH muscle.
- Download our factsheet on Muscle Biopsy testing here.
Testing family members
MH is an inherited condition and once it has been found in a family testing will also be offered to other family members, to see if they are at risk. This is done in a systematic way where the closest relatives are tested first.
The choice of test will vary from family to family, depending on whether a gene change associated with malignant hyperthermia has been found or not. Where such a gene change has been found a positive gene test (blood sample) will define high risk for malignant hyperthermia under anaesthesia.
However because of the possibility of more than one gene change being responsible for MH in some families, a negative gene change must be confirmed by the muscle biopsy tests. It is only through the muscle biopsy tests that someone who is possibly at increased risk of MH can be shown not to be at risk.
The muscle biopsy tests can only be done in adults and children more than 10 to 12 years of age. There is also a minimum body weight for a child of 30 kg. These limitations on the muscle biopsy are principally because there is uncertainty of the accuracy of the biopsy tests in younger children. There is also some concern that the muscle biopsy may have an unacceptable cosmetic result in younger children.
- Download our factsheet on Muscle Biopsy testing here.