Doctors can check patients' DNA (search) when choosing medication for them, using a test the Food and Drug Administration said Thursday it has approved.

The FDA called it the first laboratory test system for doctors to use in reviewing patients' genetic information. It is meant to improve doctors' ability to prescribe medications for conditions such as cancer and heart and psychiatric diseases.

"Physicians can use the genetic information from this test to prevent harmful drug interactions and to assure drugs are used optimally, which in some cases will enable patients to avoid less effective or potentially harmful treatment choices," said acting FDA commissioner Lester M. Crawford.

The new test is the AmpliChip Cytochrome P450 Genotyping Test (search) made by Roche Molecular Systems, Inc., of Pleasanton, Calif. The FDA said the test was cleared for use with the Affymetrix GeneChip Microarray Instrumentation System, manufactured by Affymetrix, Inc., of Santa Clara, Calif.

The test uses DNA from a patient's blood. It analyzes one of the genes from a group called cytochrome P450 genes, which are active in the liver to break down certain drugs and other compounds. Variations in this gene can cause a patient to metabolize certain drugs more quickly or more slowly than average, or, in some cases, not at all, FDA said.