Medical Oncologist
CION Cancer Clinics
HLA testing before allopurinol, seizure medicines and other drugs | CION Cancer Clinics
An HLA test looks for an inherited immune type that can make one particular medicine dangerous. In cancer care the medicines involved are mostly supporting ones, such as allopurinol for uric acid and some seizure medicines. A positive result means that medicine is swapped, not that treatment stops. This page explains the known pairs, how HLA testing differs from transplant typing, and the rash signs that need same-day care. At CION Cancer Clinics, our team helps carriers and their families plan checks, next steps and support after a genetic result.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- Why would anyone need an HLA test before a medicine?
- Which HLA types matter, and for which medicines?
- The words you will meet, in plain language
- Is this the same HLA test used for a bone marrow transplant?
- What this page cannot tell you
- Four things patients tell us, and what is actually true
- Common questions about HLA testing before medicines
The short answer
Why would anyone need an HLA test before a medicine?
Some people inherit an immune system type that reacts violently to one particular medicine. The reaction is rare, but it can cause severe blistering of the skin or damage to the liver. An HLA test looks for that inherited type before the medicine is given, so a safer alternative can be chosen.
What HLA actually is
HLA genes make the markers your immune system uses to tell your own cells from germs. They differ enormously between people and between communities. Almost always that variety is harmless. With a handful of medicines, one specific HLA type allows the drug to confuse the immune system into attacking the body.
Where this meets cancer care
The medicines involved are mostly not chemotherapy. They are the supporting medicines given alongside it. Allopurinol, used to prevent a build-up of uric acid when blood cancers are first treated, is the most common one. Anti-seizure medicines given for brain tumours are another. Knowing your HLA type in advance can steer those choices.
This is an inherited result about your immune system. It says nothing about your cancer or your family's cancer risk.The known pairs
Which HLA types matter, and for which medicines?
Each warning links one HLA type to one medicine or family of medicines. A positive result for one says nothing about the others.
HLA-B*58:01 and allopurinol
Carriers have a much higher chance of a severe skin reaction to allopurinol. This type is found in many Asian populations, including in India. Other uric acid medicines can usually be used instead.
HLA-B*15:02 and seizure medicines
Linked to severe skin reactions with carbamazepine, oxcarbazepine and phenytoin. These may be prescribed for seizures caused by a brain tumour, or carbamazepine for nerve pain. South Asians carry this type more often than Europeans do.
HLA-A*31:01 and carbamazepine
A second type linked to reactions with the same drug, including a widespread rash with fever and organ involvement. It is tested less often in India.
Cancer drug labels that mention HLA
The labels of lapatinib and pazopanib note HLA types linked to liver injury. Testing before these drugs is not routine. Your team will usually rely on regular liver blood tests instead.
Not sure whether this applies to you?
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Signs that cannot wait
After starting any new medicine, a rash that spreads quickly, blisters, peeling skin, sores in the mouth or eyes, or a rash with fever and a swollen face needs an emergency department the same day. Take the medicine strip with you and say when you started it. Do not take the next dose, and do not treat the rash at home first.
On your report
The words you will meet, in plain language
- HLA
- Human leukocyte antigen. The family of genes that make the immune system's identity markers.
- Allele
- One version of a gene. HLA-B*58:01 is one allele of the HLA-B gene, written with a star and a colon.
- Positive or carrier
- You have at least one copy of the allele tested for. One copy is enough to raise the risk with that medicine.
- Negative or not detected
- The allele was not found. The specific high-risk link does not apply to you, though other reactions remain possible.
- Stevens-Johnson syndrome
- A severe reaction in which the skin and the lining of the mouth and eyes blister and peel. It needs hospital care.
- DRESS
- A drug reaction with a widespread rash, fever and inflammation of organs such as the liver. It can appear weeks after starting a medicine.
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Same genes, different question
Is this the same HLA test used for a bone marrow transplant?
HLA test before a medicine
HLA typing for a transplant
Looks for one or two specific alleles
Reads several HLA genes in detail
Answers whether one medicine is safe
Answers which donor is the closest match
Done once, for the patient only
Done for the patient and possible donors
Usually a single, cheaper test
A detailed report may already answer the medicine question
Being straight with you
What this page cannot tell you
It cannot tell you whether a medicine you have already been taking safely for months is a risk. Most of these reactions start in the first weeks of a new medicine. Someone who has taken a drug for a long time without a problem is in a very different position from someone about to start it.
It cannot read your own report
HLA reports use dense codes, and a detailed transplant report may or may not include the allele that matters for a given medicine. What your specific result means is a question for the doctor who ordered the test, or for the doctor planning to prescribe.
Who this does not apply to
Most people having cancer treatment do not need an HLA test. If your plan does not include allopurinol, carbamazepine, oxcarbazepine or phenytoin, it is unlikely to change anything. A negative result is also not a promise of safety. Reactions can happen in people without any of these alleles, so any new rash still needs attention. And this is not the tumour test that guides targeted drugs.
Commonly believed
Four things patients tell us, and what is actually true
"A negative HLA test means I cannot react to the medicine."
It removes one known, strong risk. It does not remove every risk. People without the allele can still have a reaction, so any new rash or fever after a new medicine needs to be reported.
"If I am positive, I must avoid all medicines."
The link is specific. A person with HLA-B*58:01 needs to avoid allopurinol, not every tablet. Your doctor will name exactly which medicines the result applies to.
"This is only a problem for Chinese or Thai patients."
These alleles are well studied in East and Southeast Asia, but they are also found in India. How common they are varies from one community to another, which is why ancestry alone is not a safe guide.
"A skin reaction means I was given the wrong dose."
These reactions are about the immune system, not the dose. They can happen at an ordinary, correctly prescribed dose, which is why the inherited type matters more than the amount.
Questions we are asked
Common questions about HLA testing before medicines
Do I need an HLA test before allopurinol?
It is worth asking about, because HLA-B*58:01 is found in India. In practice allopurinol is often needed within a day of starting treatment for a blood cancer, before a result could come back. Your team may choose a different uric acid medicine instead of waiting for the test.
Do I need a test before carbamazepine or phenytoin?
For people of South or Southeast Asian ancestry, drug labels advise HLA-B*15:02 testing before starting carbamazepine. Many neurologists and oncologists now choose seizure medicines that do not carry this risk. Ask which medicine you are being given and whether it needs a test.
How is the test done?
A blood sample or a cheek swab. No fasting is needed. The result reads genes you were born with, so it never needs repeating. Ask for a printed copy and keep it with your other medical papers.
My bone marrow transplant workup included HLA typing. Is that enough?
Sometimes. Detailed transplant typing often reads HLA-B in enough detail to show whether B*58:01 or B*15:02 is present. Ask your transplant team to check the report rather than ordering a new test straight away.
I took allopurinol before without a problem. Am I safe?
A previous course without any reaction is reassuring. It is not a formal test result, however, and a new course should still be discussed with your doctor. Tell them exactly when and how long you took it before.
Should my family be tested because I am positive?
Each child of a parent with one copy has a one in two chance of inheriting the allele. A relative would only need to know if they are ever prescribed the linked medicine. Telling them about your result lets them mention it to their own doctor.
How long does the result take?
It depends on the laboratory and whether the sample has to travel. Ask the lab directly before the sample is taken. If the result cannot arrive before treatment must start, a different medicine is usually the safer choice.
Can I still get my cancer treatment if I am positive?
Yes. A positive result almost always affects a supporting medicine, not the cancer treatment itself. Your team simply swaps that medicine for an alternative, and the main plan carries on as intended.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
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Sources
- Clinical Pharmacogenetics Implementation Consortium (CPIC) — Guideline for Allopurinol and HLA-B
- Clinical Pharmacogenetics Implementation Consortium (CPIC) — Guideline for Carbamazepine and HLA-B
- MedlinePlus Genetics — HLA-B gene
- U.S. Food and Drug Administration — Table of Pharmacogenomic Biomarkers in Drug Labeling
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
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G6PD deficiency and cancer drugsAnother inherited check that decides the uric acid medicineWhich cancer drugs have a gene test firstThe full short list of drug-gene checksAsking for a drug-gene test before treatmentHow to raise it with your team, and whenCarrying your drug-gene result forwardKeep the result where every future doctor will see it
Talk to us
Not sure whether your treatment plan needs an HLA test?
Tell us which medicines you have been prescribed. An oncologist will check whether any of them carry an HLA warning. One helpline serves every CION centre.