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CMAJ. 2010 May 18; 182(8): 804.
PMCID: PMC2871209

Predictive genotype

Shinya Ito, MD
Division of Clinical Pharmacology and Toxicology, Hospital for Sick Children, University of Toronto, Toronto, Ont

The article by Fernando and Broadfoot1 summarizes the important issues of drug-induced severe skin reactions. It is very important to note that genotype-based identification of those Han Chinese patients who may develop severe skin reactions to carbamazepine is now possible. However, we need to clearly understand a downside of this approach. Namely, a positive predictive value of the HLA-B*1502 genotyping is only 7.7%, as the authors suggested, or may be even less. The authors’ statement that “in 3% of patients who are test-positive, the disease may never develop with exposure to carbamazepine” could be interpreted in different ways. Because the 3% is a false positive rate of the genotyping test in Han Chinese, it is better to state as follows: “If we test 1000 Han Chinese patients who will never develop the severe skin reactions to carbamazepine, 30 of them (3%) will be positive on the HLA-B*1502 genotyping.”

Footnotes

For the full letter, go to: www.cmaj.ca/cgi/eletters/182/5/476#322816

REFERENCE

1. Fernando SL, Broadfoot AJ. Prevention of severe cutaneous adverse drug reactions; the emerging value of pharmacogenetic screening. CMAJ. 2010;182:476–80. [PMC free article] [PubMed]

Articles from CMAJ : Canadian Medical Association Journal are provided here courtesy of Canadian Medical Association