ABACAVIR HYPERSENSITIVITY — HLA-B*57:01

Abacavir Hypersensitivity — HLA-B*57:01, the variant that makes abacavir an HIV treatment for most but a potentially life-threatening hypersensitivity reaction for the 5-8% of Europeans who carry it.

Whole genome sequencing provides complete HLA class I typing — including the HLA-B*57:01 allele that the FDA mandates screening for before abacavir is prescribed — alongside all other pharmacogenomic relevant HLA alleles.

HLA-B

About this condition

Abacavir Hypersensitivity — HLA-B*57:01

Abacavir (Ziagen) is a nucleoside reverse transcriptase inhibitor (NRTI) used as a core component of combination antiretroviral therapy for HIV infection. Approximately 5-8% of patients prescribed abacavir without prior HLA-B*57:01 screening develop a potentially life-threatening hypersensitivity reaction (HSR) characterized by fever, rash, gastrointestinal symptoms, and malaise beginning within the first 6 weeks of therapy. In patients who develop HSR and then inadvertently re-challenge with abacavir — for example, if the diagnosis was not clearly documented — the reaction can be severe and rapidly fatal, with acute hypotension and multi-organ failure.

The association between HLA-B*57:01 and abacavir hypersensitivity is one of the strongest pharmacogenomic associations in medicine. HLA-B*57:01 carriers who receive abacavir have approximately a 50-60% risk of developing HSR, compared to approximately 0-1% in non-carriers. The mechanism involves the HLA-B*57:01 protein presenting abacavir or its metabolites as part of the peptide-binding groove to CD8+ T cells, triggering a polyclonal cytotoxic T cell response. HLA-B*57:01 is present in approximately 5-8% of European ancestry individuals, 1-3% of African ancestry individuals, and under 1% of Asian ancestry individuals, making screening particularly impactful in European-ancestry HIV populations.

The FDA added a boxed warning to abacavir in 2008 requiring HLA-B*57:01 screening before or at the time of initiating abacavir therapy. WHO HIV treatment guidelines likewise recommend HLA-B*57:01 screening before abacavir use. Implementation of universal pre-treatment screening has reduced the incidence of immunologically confirmed abacavir HSR by approximately 50%. The test is standard of care in HIV treatment in the United States, European Union, and increasingly in low-and-middle-income countries. HLA-B*57:01 is also associated with flucloxacillin-induced liver injury and carbamazepine hypersensitivity risk, making complete HLA typing — as provided by whole genome sequencing — broadly valuable in patients with complex medication regimens.

Gene locus: HLA-B (6p21.33)

Single HLA-B57:01 commercial tests exist and are standard of care before abacavir. What whole genome sequencing adds is comprehensive HLA typing — covering HLA-B15:02, HLA-B58:01, and other clinically actionable HLA alleles alongside B57:01 in a single test.

Complete HLA typing covers multiple life-critical drug hypersensitivity alleles in one result

HLA-B*57:01 is just one of several HLA alleles with documented drug hypersensitivity associations. HLA-B*15:02 (carbamazepine-SJS/TEN in Southeast Asian populations), HLA-B*58:01 (allopurinol-SJS/TEN), HLA-B*57:01 (flucloxacillin liver injury), and HLA-A*31:01 (carbamazepine hypersensitivity in Europeans) are all clinically actionable alleles with distinct geographic distributions and drug-specific associations. A patient receiving multiple medications may have multiple relevant HLA pharmacogenomic considerations. Whole genome sequencing performs complete high-resolution HLA class I and II typing — providing the complete HLA pharmacogenomic profile in a single test rather than ordering separate single-allele tests for each relevant drug.

HLA-B*57:01 status is a permanent result — the same genome that predicts abacavir risk also informs lifelong prescribing decisions

Unlike many clinical laboratory results that require periodic re-testing, HLA genotype is fixed at birth and never changes. A HLA-B*57:01 result obtained once — whether from a targeted test or whole genome sequencing — is valid for life. The abacavir prescribing contraindication applies regardless of HIV treatment stage or co-morbidities. For patients with HIV who may change treatment regimens over many years, having the HLA genotype permanently documented in the medical record ensures that abacavir-containing regimens are avoided at every future treatment decision point without requiring repeat testing.

Abacavir Hypersensitivity — HLA-B*57:01, the variant that makes abacavir an HIV treatment for most but a potentially life-threatening hypersensitivity reaction for the 5-8% of Europeans who carry it.

Abacavir Hypersensitivity — HLA-B*57:01

Single HLA-B*57:01 commercial tests exist and are standard of care before abacavir. What whole genome sequencing adds is comprehensive HLA typing — covering HLA-B*15:02, HLA-B*58:01, and other clinically actionable HLA alleles alongside B*57:01 in a single test.

Complete HLA typing covers multiple life-critical drug hypersensitivity alleles in one result

HLA-B*57:01 status is a permanent result — the same genome that predicts abacavir risk also informs lifelong prescribing decisions

Others in Pharmacogenomics

One test. A lifetime of answers.

Single HLA-B57:01 commercial tests exist and are standard of care before abacavir. What whole genome sequencing adds is comprehensive HLA typing — covering HLA-B15:02, HLA-B58:01, and other clinically actionable HLA alleles alongside B57:01 in a single test.