A malignant hyperthermia genetic test looks mainly for pathogenic variants in RYR1 and, less often, CACNA1S or STAC3. These genes control calcium movement in skeletal muscle. A susceptible person can develop a life-threatening hypermetabolic crisis after exposure to volatile inhaled anesthetics or the muscle relaxant succinylcholine. Genetic testing can confirm susceptibility when a known disease-causing variant is found, guide testing of relatives, and help anesthesia teams avoid triggers. However, a negative genetic result does not rule out malignant hyperthermia susceptibility because current testing does not identify every cause. In some people, the definitive evaluation is a specialized muscle contracture test called the caffeine-halothane contracture test in North America or in vitro contracture test in Europe. Anyone with a convincing personal or family history should be managed as susceptible until an expert center completes the evaluation. Safe non-triggering anesthesia is available, and planned surgery does not need to be avoided when the anesthesia team is informed and prepared.
- RYR1 causes most genetically explained malignant hyperthermia susceptibility; CACNA1S and STAC3 account for fewer cases.
- A pathogenic or likely pathogenic variant can establish inherited susceptibility.
- A negative panel cannot reliably clear someone for trigger anesthetics.
- A variant of uncertain significance is not a confirmed diagnosis, but the clinical history may still require trigger avoidance.
- Volatile anesthetics and succinylcholine are the main recognized anesthetic triggers.
- Relatives need targeted testing or expert physiologic testing based on the family result.
Table of Contents
- What malignant hyperthermia is
- Who should be evaluated
- Genetic and muscle contracture tests
- Interpreting test results
- Safe anesthesia after a result
- Inheritance and family testing
- RYR1-related muscle and heat conditions
- Records, alerts, and next steps
What malignant hyperthermia is
Malignant hyperthermia, or MH, is an inherited disorder of skeletal-muscle calcium regulation. During exposure to a triggering anesthetic, uncontrolled calcium release causes sustained muscle metabolism and contraction. The body rapidly produces carbon dioxide, acid, heat, and potassium while using large amounts of oxygen and energy. Without prompt treatment, the crisis can lead to muscle breakdown, dangerous heart rhythms, kidney injury, clotting problems, brain injury, or death.
The name can be misleading because high temperature is often a later sign. Early clues during anesthesia include an unexpected rise in exhaled carbon dioxide despite increased ventilation, fast heart rate, generalized or jaw muscle rigidity, acidosis, and rapidly increasing oxygen consumption. Hyperkalemia, very high creatine kinase, dark urine from myoglobin, and rising core temperature may follow. A reaction can begin soon after exposure or develop more gradually.
The main triggers are potent volatile inhaled anesthetics, including agents such as sevoflurane, desflurane, and isoflurane, and the depolarizing muscle relaxant succinylcholine. Nitrous oxide is not a volatile MH trigger. Intravenous anesthetics such as propofol, opioids, local anesthetics, and nondepolarizing muscle relaxants can be used in a trigger-free plan when otherwise appropriate. The anesthesiologist determines the safest combination for the procedure and patient.
Susceptibility is usually silent. A person can have several uneventful anesthetics and still experience MH during a later exposure. Lack of a prior reaction does not prove safety because trigger dose, procedure, anesthetic combination, age, and chance may differ. Likewise, a relative’s normal surgery does not exclude an inherited familial variant.
MH is not the same as fever from infection, heat stroke, serotonin syndrome, neuroleptic malignant syndrome, thyroid storm, sepsis, or inadequate anesthesia. These conditions can resemble parts of an MH crisis. An anesthesiology review of the timing, medications, vital signs, blood gases, CK, potassium, temperature, treatment response, and postoperative course helps determine how likely MH was.
Dantrolene is the specific emergency treatment because it reduces abnormal calcium release from skeletal muscle. In a crisis, the anesthesia team stops triggers, gives dantrolene promptly, provides high-flow oxygen and active cooling when needed, corrects acidosis and electrolyte problems, treats complications, and continues monitoring for recurrence. Genetic testing is performed after stabilization; it is not an emergency diagnostic tool during the event.
Who should be evaluated
Evaluation is appropriate after a suspected MH reaction during or shortly after anesthesia. The most informative first person is usually the one who had the event. Medical records should be obtained before testing whenever possible. A vague family story of “anesthesia allergy,” fever, cardiac arrest, or unexplained surgical death may be important, but it needs reconstruction because many perioperative complications are unrelated to MH.
Relatives of a person with confirmed MH susceptibility should also be assessed. Confirmation may come from a pathogenic genetic variant or a positive muscle contracture test. Until their status is clarified, close relatives are often advised to receive non-triggering anesthesia. The exact degree of relationship and which side of the family is involved determine risk.
Testing may be considered for people with recurrent exertional rhabdomyolysis, severe heat illness, or certain congenital myopathies, especially when RYR1 involvement is suspected. The overlap is real but incomplete. Most exercise cramps or heat exhaustion do not indicate MH susceptibility, and not every RYR1 myopathy variant carries the same anesthetic risk. A neuromuscular and MH expert should frame the question before the laboratory order.
An incidental RYR1 or CACNA1S variant may be found during exome or genome sequencing for another reason. Some laboratories actively report selected medically actionable variants. The next step depends on classification. A recognized pathogenic MH variant is clinically important even if the person has never had anesthesia. A VUS is not enough by itself to label someone genetically susceptible, but the anesthesia plan may remain cautious while the finding and history are reviewed.
People planning surgery do not need to wait for complete testing if MH is suspected. The procedure can often proceed with a prepared anesthesia machine, avoidance of triggering drugs, standard monitoring, and immediate access to appropriate emergency resources. MHAUS and the European Malignant Hyperthermia Group advise managing an untested at-risk person as susceptible when the question has not been resolved.
Routine population screening is not currently standard. MH-associated variants are difficult to classify, penetrance is incomplete, and a negative panel has limited sensitivity. Testing is most useful when anchored to a personal event, confirmed family finding, suggestive muscle phenotype, or a carefully evaluated incidental result.
Before testing, ask whether the laboratory reports all three established genes, how RYR1 variants are classified, whether copy-number analysis is included, and whether the result will be reviewed by an MH diagnostic center. The quality of interpretation matters more than simply ordering a large “anesthesia panel.”
Genetic and muscle contracture tests
Genetic testing uses blood, saliva, or another DNA sample to sequence RYR1, CACNA1S, and sometimes STAC3. RYR1 accounts for most genetically explained nonsyndromic MH susceptibility. CACNA1S variants are much less common. Biallelic STAC3 variants cause Native American myopathy and can include MH susceptibility; the phenotype and inheritance differ from usual dominant RYR1- or CACNA1S-related susceptibility.
A multigene panel should include sequence analysis and, when validated, deletion/duplication testing. However, most established MH variants are single-nucleotide or small insertion/deletion changes. The central challenge is not finding rare variants; it is deciding which rare variants truly alter calcium regulation enough to cause susceptibility. RYR1 is a large gene with many benign missense changes.
The caffeine-halothane contracture test, or CHCT, is performed in North America. The in vitro contracture test, or IVCT, is used in Europe and other regions under a related but not identical protocol. Both require a surgical muscle biopsy obtained at a specialized center. Fresh muscle bundles are exposed to caffeine and halothane, and their contracture response is measured. The sample cannot usually be shipped like an ordinary biopsy, so the person must travel to an accredited testing center.
Contracture testing evaluates the muscle phenotype rather than a particular DNA variant. It can identify susceptibility in a person whose genetic panel is negative or inconclusive. It is invasive and geographically limited, but it remains an important diagnostic method. The result is commonly classified as susceptible or normal according to the center’s protocol. Borderline or protocol-specific findings need expert explanation.
Genetic testing is especially powerful after a familial pathogenic variant has been established. At-risk relatives can have a simple targeted blood or saliva test instead of muscle biopsy. A relative who tests positive is considered susceptible. A relative who tests negative for the known familial variant may be released from that variant-related risk only when the original family diagnosis and variant are well established and no separate clinical concern remains.
When no family variant is known, a negative genetic panel cannot replace contracture testing. A proportion of families with positive physiologic testing have no identifiable pathogenic variant in RYR1, CACNA1S, or STAC3. There may be undiscovered genes, hard-to-detect variants, or changes that current evidence cannot classify.
The choice between DNA testing and muscle testing depends on who is being evaluated, the urgency of surgery, the quality of the event history, access, age, and family results. Young children may not be ideal candidates for biopsy because of muscle size and procedural burden. An MH center can develop a staged plan rather than treating the tests as interchangeable.
Interpreting test results
A pathogenic or likely pathogenic variant known to cause MH susceptibility is a positive molecular result. In RYR1 or CACNA1S, one such variant is usually sufficient because susceptibility is generally autosomal dominant. The person should receive trigger-free anesthesia, and biological relatives can be offered targeted testing. The report should identify the exact transcript, DNA change, protein change, and classification evidence.
Not every RYR1 pathogenic variant has the same phenotype. Some cause central core disease, multiminicore disease, congenital fiber-type disproportion, King-Denborough syndrome, or other myopathies. Certain variants can cause both muscle weakness and anesthetic susceptibility. The clinician should review strength, motor history, CK, exercise symptoms, and family history rather than assuming the finding affects anesthesia only.
A negative result means no reportable pathogenic variant was found with that assay. It does not mean “not susceptible.” A person with a highly convincing reaction or positive contracture test should still be managed as MH susceptible despite negative sequencing. The report’s coverage, genes, variant types, and classification date should be reviewed before deciding whether additional testing or reanalysis is useful.
A VUS is a DNA change with insufficient evidence. It may eventually prove harmful or benign. It should not be used as the sole basis for predictive testing of healthy relatives because finding the same VUS does not establish risk and not finding it may not establish safety. Segregation, functional calcium-release studies, contracture testing, population frequency, and expert variant curation can help resolve some VUSs.
The clinical history can override molecular uncertainty for anesthesia safety. If the person had an event strongly compatible with MH, clinicians should not use a VUS or negative result to justify trigger exposure. Conversely, a VUS discovered incidentally in someone with no supporting history should not automatically be described as a confirmed disease-causing mutation. An individualized interim plan can prioritize safety without overstating certainty.
A benign or likely benign variant does not explain MH susceptibility. Consumer or raw sequencing data may mislabel variants because databases are outdated or context is missing. Any potentially actionable finding should be confirmed in a clinical laboratory with MH-specific classification.
A positive contracture test indicates physiologic susceptibility even if genetics is negative. A normal contracture test performed under an accepted protocol can substantially reduce concern for the tested person, but it does not directly test relatives. Family members need their own evaluation unless a familial genetic variant provides a targeted route.
A clear pathogenic, benign, and VUS result explanation is useful, but MH adds a special rule: a negative DNA test has lower exclusion power than a negative targeted test for a known family variant.
Safe anesthesia after a result
MH-susceptible people can undergo general anesthesia, regional anesthesia, sedation, dental procedures, childbirth care, and emergency surgery. The key is a trigger-free plan. The patient should tell the surgeon, anesthesiologist, dentist, emergency team, and procedural facility well in advance. The diagnosis belongs in the medication and allergy-alert area of the medical record even though it is a pharmacogenetic susceptibility rather than a conventional allergy.
The anesthesia team avoids all potent volatile anesthetics and succinylcholine. They prepare the anesthesia workstation to prevent residual vapor exposure, using the method recommended for the machine and local guideline. Activated charcoal filters may shorten preparation in some settings. Dantrolene should be immediately available wherever trigger agents are used, even when the scheduled patient is receiving a non-triggering technique.
Total intravenous anesthesia is one option, but the exact drugs depend on the person and procedure. Regional blocks, spinal or epidural anesthesia, and local anesthetics are not MH triggers. Nondepolarizing neuromuscular blockers are generally considered safe from an MH standpoint. The team still manages ordinary anesthetic risks, allergies, airway issues, heart disease, pregnancy, kidney function, and medication interactions.
Prophylactic dantrolene is not routinely recommended when triggers are avoided. It can cause weakness and other adverse effects and is unnecessary for a properly prepared trigger-free anesthetic. Standard preoperative fasting, monitoring, and recovery arrangements generally apply unless other medical issues require changes. Susceptible patients may have outpatient procedures in appropriately prepared facilities.
A prior uneventful anesthetic is not a reason to use triggers. The patient should not be challenged with a volatile anesthetic to “see what happens.” Deliberate exposure is dangerous and is not a diagnostic test. Likewise, routine surgery should not be canceled solely because contracture testing is unavailable; safe management as susceptible is usually possible.
During general anesthesia, continuous monitoring includes exhaled carbon dioxide and appropriate core temperature monitoring for procedures of relevant duration. Staff must recognize early signs and have an MH response protocol. Prompt treatment matters more than waiting for every diagnostic feature, especially fever.
After surgery, routine recovery may be appropriate after an uneventful trigger-free anesthetic. Extended observation is based on the procedure and clinical course rather than susceptibility alone. If an actual MH crisis occurs, intensive monitoring is needed because complications and recurrence can develop after initial treatment.
Inheritance and family testing
Most RYR1- and CACNA1S-related MH susceptibility is autosomal dominant. Each child of a carrier has a 50% chance of inheriting the variant. The same probability applies to siblings when a parent carries it. Inheriting the variant creates susceptibility, but not every exposure causes a crisis and not every carrier is ever exposed to a trigger.
A person can appear to be the only affected family member because relatives had no surgery, received non-triggering anesthesia, had uneventful trigger exposure, or were never recognized. Penetrance depends on exposure as well as biology. Therefore, an unremarkable anesthesia history in a parent does not rule out carrier status.
When a pathogenic familial variant is known, targeted testing is offered to adult relatives and may be considered in children because the result can change anesthesia management during childhood. This differs from predictive testing for a condition with no childhood action. Testing before a planned procedure allows a clear record, but untested at-risk children can still receive trigger-free anesthesia safely.
If an at-risk relative tests positive, they should receive written guidance and inform their health professionals. If they test negative for the confirmed family variant, the MH center determines whether they can be considered not susceptible. A separate suspicious anesthetic event, muscle disorder, or variant on the other side of the family may require independent evaluation.
When the affected family member has only a positive contracture test and no pathogenic variant, relatives cannot be cleared by a negative gene panel. They may choose their own contracture testing or continue to be managed as susceptible. Testing the most informative person first prevents false reassurance.
STAC3-related Native American myopathy is autosomal recessive. Affected people usually have two pathogenic variants and may have congenital weakness, distinctive features, and MH risk. Carrier relatives generally do not follow the same risk model as dominant RYR1 families. Gene-specific counseling is essential.
Reproductive options can be discussed after a familial variant is confirmed. Prenatal diagnosis and preimplantation genetic testing are technically possible, but families weigh them differently because susceptibility is preventable through anesthetic avoidance and expression is variable. Counseling should provide options without implying that reproductive testing is required.
A family letter should include the exact gene and variant, the name of the diagnosing center, and the recommendation to seek MH-specific counseling. It should not rely on the phrase “anesthesia reaction,” which is too broad for accurate targeted testing.
RYR1-related muscle and heat conditions
RYR1 is also associated with congenital and adult-onset muscle disease. Some people have lifelong hypotonia, delayed motor milestones, proximal weakness, scoliosis, eye-movement limitations, or characteristic biopsy findings. Others have normal baseline strength but experience exertional muscle pain, cramps, high CK, or rhabdomyolysis. The phenotype depends on the exact variant and whether one or both gene copies are affected.
Exertional rhabdomyolysis is rapid muscle breakdown associated with severe exercise, heat, illness, fasting, drugs, or a genetic predisposition. Symptoms can include severe muscle pain, weakness, swelling, and cola-colored urine. It can cause dangerous potassium abnormalities and kidney injury. Anyone with dark urine or severe muscle symptoms after exercise or heat needs urgent medical assessment, not just outpatient genetic counseling.
Some RYR1 carriers appear more vulnerable to exertional heat illness. However, classic environmental heat stroke is not identical to anesthetic MH, and most heat illness is not caused by RYR1. A history of heat intolerance should be evaluated alongside hydration, environment, medications, exertion, infection, and other metabolic or muscle conditions.
Advice should be individualized. People with recurrent RYR1-related rhabdomyolysis may be told to avoid extreme heat, sudden unaccustomed maximal exercise, dehydration, and exercise during illness, while maintaining appropriate regular activity. A neuromuscular specialist can develop a plan for hydration, gradual conditioning, emergency symptoms, medication review, and CK monitoring when useful.
The presence of an RYR1 myopathy often supports trigger-free anesthesia even when the specific variant’s MH evidence is incomplete. Anesthesia planning should involve both the neuromuscular diagnosis and variant classification. Some congenital myopathies also create respiratory weakness, scoliosis, aspiration, or difficult-airway risks independent of MH.
CACNA1S variants can cause hypokalemic periodic paralysis as well as MH susceptibility through different variants. Episodes of flaccid weakness related to low potassium, carbohydrate intake, rest after exercise, or illness require a separate neurologic evaluation. The label “CACNA1S positive” is not specific enough; the exact variant and phenotype determine the implication.
A broad neurologic genetic panel may identify these genes, but the report must distinguish myopathy, periodic paralysis, and MH evidence. One gene can support several diagnoses, and the anesthesia recommendation should not be inferred from gene name alone.
Records, alerts, and next steps
After a suspected crisis, request the anesthesia record, medication administration record, vital-sign trends, laboratory results, discharge summary, and dantrolene documentation. Referral to an MH investigation center should occur after recovery. The center can calculate clinical likelihood, select genetic or contracture testing, and advise relatives.
After a positive genetic or contracture result, obtain a concise written letter stating that the person is MH susceptible and requires non-triggering anesthesia. Keep copies in the primary-care record, hospital portal, and personal files. A medical alert bracelet or phone emergency card can list “malignant hyperthermia susceptible—avoid volatile anesthetics and succinylcholine.”
Before every procedure, contact the anesthesia service rather than relying only on an electronic allergy field. Ask whether the facility can provide trigger-free anesthesia, prepare the workstation correctly, monitor appropriately, and access dantrolene. This is particularly important for dental offices, ambulatory centers, remote locations, and emergency procedures.
After a negative genetic result, do not remove alerts without expert review if the personal or family history remains concerning. Ask whether contracture testing is indicated and whether the panel included all relevant genes and current variant interpretation. A negative test in the wrong family member may add little information.
After a VUS, seek review by an MH center or genetics professional familiar with RYR1 curation. Ask whether the variant appears on expert lists, whether functional or segregation studies exist, and whether the laboratory will issue reclassification updates. Until the clinical risk is resolved, a non-triggering plan is usually the safer interim approach when there is a credible history.
People who have no procedure planned can still complete testing and family communication. Emergency surgery is not the ideal time to reconstruct records. Early documentation allows anesthesiologists to prepare without delaying necessary care.
During a possible crisis, clinicians should activate the facility’s MH protocol and obtain immediate expert support through the appropriate regional service. Patients and families should not try to direct emergency dosing from an article. The lasting lesson is straightforward: a positive result can prevent a crisis, a negative result may not exclude susceptibility, and clear communication makes safe anesthesia possible.
References
- Nonsyndromic Malignant Hyperthermia Susceptibility (2025, GeneReviews)
- European Malignant Hyperthermia Group Guidelines for Investigating Malignant Hyperthermia Susceptibility (2026)
- Testing for Malignant Hyperthermia (2025, Malignant Hyperthermia Association of the United States)
- Testing for Malignant Hyperthermia Susceptibility (2025, European Malignant Hyperthermia Group)
- Malignant Hyperthermia Panel, Sequencing: Test Fact Sheet (2025, ARUP Consult)
- EMQN Best Practice Guidelines for Genetic Testing and Reporting of RYR1-Related Disorders (2026)
Disclaimer
This article is for general education and does not replace advice from an anesthesiologist, malignant hyperthermia center, neuromuscular specialist, or genetic counselor. A negative genetic test does not necessarily make triggering anesthesia safe. During a suspected malignant hyperthermia crisis or severe exertional rhabdomyolysis, seek immediate emergency medical care and follow the treating team’s protocol.
