| Monday, January 01, 0001
A simple diagnostic lab test can help you avoid adverse drug interactions, improve drug efficacy – and prescribe more confidently.
Personalized medicine offers the promise of optimizing drug therapy for each, individual patient. Since collectively, our bodies, organs, enzymes and genes are all unique, not all patients respond appropriately to a standard, one-size-fits-all approach to drug therapy. A single DNA test provides a lifetime of knowledge about a patient's drug sensitivity and rate of drug metabolism, which are central to optimizing drug selection and thereby protecting against drug toxicity or reduced efficacy.
Genetic tests of the P450 cytochrome system have become available through specialty laboratories over the past decade, with acceptance first seen in the cardiology community. New this year, however, CMS has added new codes to the Physician Fee Schedule, facilitating 100% coverage for some of these tests. Many of the private insurers have followed suit and also reimburse for these tests, effectively broadening the availability of this tool for physicians and patients.
Given the wide-ranging applicability of this test, we thought we would provide a brief overview for our readers. More information is available here.
The vast majority of drugs are metabolized through the liver and the P450 cytochrome system of drug metabolizing enzymes (DMEs). This includes CYP2C9, CYP2C19, CYP2D6, CYP3A4 and CYP1A2. In fact, the P450 system metabolizes over 50% of today's most commonly prescribed drugs.
The function of one or more of these DMEs can be affected by gene variants. Patients with gene variants (5%-45% depending on ethnicity) are more likely to experience drug toxicity or lack of efficacy because the altered enzyme function can change the rate at which the liver metabolizes drugs. Most variants cause a loss of enzyme function and patients with reduced enzyme function are poor or intermediate metabolizers. Fewer people have variants thatincrease enzyme function and these patients are rapid or ultra-rapid metabolizers. And, of course, many people have a normal drug metabolism profile.
Clinical Utility & Rationale
The P450 cytochrome pathway is well known in the cardiology community, with leading institutions, such as Scripps, Vanderbilt, the Mayo Clinic and others incorporating routine testing for variations of the C2YP19 gene. In particular, for patients on or candidates for blood thinner therapy, Vanderbilt "believes the real utility of this strategy will be in the outpatient setting", performing the test well in advance of the patient needing an antiplatelet agent.
A recent study by Medco and the Mayo Clinic showed that ordering a P450 cytochrome-related test early – prior to starting therapy – reduces hospitalization rates by nearly 1/3rd for patients on blood thinners. This is critically important because patients on blood thinners have the highest incidence of adverse events and highest hospitalization rate.2
The utility of the test expands well beyond warfarin and blood thinners. A landmark study in the New England Journal of Medicine showed that between 40% to 75% of drug therapy is less effective than expected.1 Knowing how your patient is likely to respond to drug therapy – or why they might be responding poorly to a current regimen – can help with drug and drug class selection. It is noteworthy that so-called polypharmacy patients (those on multiple drugs) are at the greatest risk for adverse drug reactions, as the chance that one or more of the drugs will not be metabolized correctly increases with each drug prescribed.
As an example of the broad applicability of this type of testing, we highlight the Extended DME Panel from Iverson Genetics (Bothell, Wash.).
Iverson's "DME Panel" tests for variations of 7 enzymes:
- CYP2C9 variations that affect response to warfarin, NSAIDs, fluvastatin, rosuvastatin, and others
- CYP2C19 variations affect response to clopidogrel, tricyclics, anticonvulsants, and others
- CYP2D6 variations that affect codeine response, antiarrhythmics, beta blockers, SSRIs and others
- CYP3A4 variant affects the response to atorvastatin, simvastatin and lovastatin, psychotropics, and others
- CYP1A2, which can affect response to acetaminophen and Haldol, and others
- VKORC1 affects a patient's sensitivity to warfarin. COMT metabolizes catecholamine drugs such as dopamine, methyldopa and levodopa
Samples are collected via a buccal swab or blood draw and shipped to the laboratory; test results and the report are returned within 24 hours of receipt.
Billing and Economics
For the Iverson test panel and certain other suppliers' panels, Medicare coverage extends to all CMS carriers in all localities. As noted earlier, many private insurers also cover the test.
Laboratories like Iverson bill insurers directly; there is no cost to the practice for the test or test results, and no patient copays to collect. There is, of course, a "soft cost" – the time required for sample collection, analyzing the results and making subsequent treatment decisions, as warranted.
There are revenue components for physicians and their practices:
- Interpretation via CPT Code G0452-26, Molecular pathology interpretation. The Medicare reimbursement ranges from $16.30 to $25.00 with a national median of $18.71.
- Elevated E/M coding. Patients with abnormal variants will need medications reviewed, drug selection strategies assessed, and counseling on the life-long impact of these results
This diagnostic lab testing provides clinically useful information for patients on or about to be prescribed drugs that are metabolized by this system – about half the commonly prescribed drugs. Sample collection, shipping and the report are all straightforward. Medicare's coverage of the test broadens it's utility to all prescribers. And, while the clinical benefit of the test provides a compelling rationale for incorporating the test into your prescribing protocols, there also are modest but meaningful revenue opportunities for the physician and practices associated with the test.
More test information is available at physiciansofficeresource.com.
Sean Hanlon is POR's senior diretor of professional communications. He has held senior marketing, reimbursement management and distribution management positions for diagnostics companies and has managed strategic marketing programs for Boston Scientific, Medtronic, Genentech, Bristol-Myers Squibb and other leading companies. He blogs for POR at blog.physiciansofficeresource.com and can be reached @poronline and @smhanlon on Twitter.