The use of medication may affect diagnostic tests. This may distort the results of those tests. Because laboratories are often unaware of the medication a patient is using, it may not always be immediately clear that a medicinal product is the cause of a deviating test result. This is evident from research conducted by RIVMNational Institute for Public Health and the Environment on behalf of the Health and Youth Care Inspectorate (IGJ).

The influence of medication, so-called interference, is not always known at the time a diagnostic test (such as a blood test) is being developed. In some cases, the interference becomes known after the IVD has been put on the market and used in laboratories. In Europe, a database is being created where laboratories, test manufacturers and pharmaceutical companies will be able to find information about this in the future. 

If the interference of a medicinal product with a diagnostic test is discovered, the manufacturer of the IVD (a diagnostic test in a laboratory) will amend the instructions for use. Then laboratories know that they have to consider this interference when using the IVD.

It is unknown how often medicines influence diagnostic tests.  The Health and Youth Care Inspectorate receives one or two reports of newly discovered interferences per year. It may happen that they are not discovered, but new regulations can improve this. It should be noted that a physician does not base his judgment exclusively on an IVD test. A physician also often carries out other tests for diagnosis and considers the symptoms and complaints of the patient.