Predictive genotype
===================

* Shinya Ito
* Bruce C. Carleton

The article by Fernando and Broadfoot 1 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](http://www.cmaj.ca/cgi/eletters/182/5/476#322816)

## REFERENCE

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