# A nurse is preparing to initiate carbamazepine for a client of Han Chinese descent with new-onset trigeminal neuralgia. Which pre-treatment test is most important?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=391742&lang=en  
> language: en  
> subject: Standard/Transmission-Based Precautions/Surgical Asepsis  
> category: SIPC

## Question

A nurse is preparing to initiate carbamazepine for a client of Han Chinese descent with new-onset trigeminal neuralgia. Which pre-treatment test is most important?

## Option

1. HLA-B*1502 genetic test **✔ Correct answer**
2. Serum sodium
3. CBC
4. Liver function test

**Correct answer: 1**

## Explanation

Correct (2): HLA-B*1502 is strongly associated with carbamazepine-induced Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN); the allele is most prevalent in Han Chinese, Thai, and other Southeast Asian populations. FDA mandates screening before initiation. Carriers must use an alternative anticonvulsant. (1) CBC monitors aplastic anemia long-term but is not the gating screen. (3,4) Sodium and LFT are monitored on therapy but are not the pre-screen for life-threatening hypersensitivity.

## In-depth explanation

Memory Tip Carbamazepine = "C for Chinese screening" — HLA-B*1502 in Asians; HLA-B*5701 (abacavir, different drug) shows similar pharmacogenomic gating.

## Clinical scenario

Scenario 42-year-old female of Han Chinese descent with trigeminal neuralgia; provider prescribes carbamazepine 200 mg PO BID. No prior anticonvulsant exposure.

## Key concepts

- **HLA-B*1502** — Genetic marker strongly linked to carbamazepine-induced SJS/TEN; screening required in Asian-descent clients before initiation.
- **Stevens-Johnson syndrome** — Severe mucocutaneous reaction with epidermal detachment; can be fatal; carbamazepine is one of the highest-risk triggers.
- **Pharmacogenomic screening** — Genetic testing used to predict serious drug reactions and tailor therapy; standard for HLA-B*1502 with carbamazepine in at-risk ancestries.

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