By Kirell Lakhman

This update includes details provided by a Scripps Health spokesperson.

Quest Diagnostics later this month plans to offer nationwide a PCR-based assay designed to predict response to the anticoagulant Plavix.

The LDT, Quest’s first saliva-based test with a cardiovascular indication, interrogates the cytochrome P-450 2C19 gene for one or four mutations known to affect how the body metabolizes the drug, known generically as clopidogrel.

The wild type version of the gene is CYP2C19*1, while the *2, *3, *4, and *5 variants affect metabolism.

Quest is currently offering the test as a pilot program to physicians at a Scripps Health hospital who can prescribe it to patients undergoing elective coronary stent procedures, the lab said in a statement Wedneaday.

The facility, Scripps Green Hospital in San Diego, has access to a spit-based version of the assay (patients can collect samples at their doctor’s office or at home), though Quest said it plans to co-launch a blood-based version nationwide later this month. A Quest spokesperson told me the company is currently ”making other [hospital] clients aware of” it.

The assay, which costs around $200, has a “targeted turnaround time” of about four days, according to the spokesperson.

A Scripps Health spokesperson told me the hospital that will be providing the test (it has five acute-care facilities in San Diego county) performs around 1,800 coronary stent procedures each year, 70 percent of which, or 1,300, are elective.

According to genetic-testing company Genelex, which is among several shops offering similar assays, “most” of the approximately 1 million patients who undergo coronary stent procedures each year in the US are prescribed Plavix. Those that carry mutated versions of the CYP2C19 gene will not likely respond well to the drug, which puts them at greater risk for adverse cardio- and neurovascular events.

Approximately two-thirds of Caucasians and 60 percent of blacks and Asians are believed to carry mutations of the gene. According to Seattle-based Genelex, about 2-6 percent of Caucasians, 15-20 percent of Japanese, and 10-20 percent of Africans have a “slow acting, poor metabolizer form of this enzyme.”

Genelex’s test, which can run off buccal swabs and blood, but not spit, interrogates the *2, *3, *4, *5, *6, *7, and *8 variants of the gene and has a turnaround time of 10 days standard and five days STAT.

Other genes believed to affect Plavix efficacy are the glycoprotein IIIa receptor and P2RY12 genes, which may alter the drug’s pharmacodynamics, according to Lexi-Comp’s Pharmacogenomics Handbook. GPIIIa may also predict the ability of antiplatelet drugs such as Plavix to prevent subacute thrombosis following coronary artery stent implantation.