The Importance of In Vitro Diagnostics
"In vitro diagnostic" refers to the purpose for which a test, kit, apparatus, control material, etc. is used. It must be intended by the manufacturer to be used with 'live' human-derived specimens - tissue samples, bodily fluids, etc. - for the purposes of investigating a condition. For example, specimen receptacles, such as urine sample receptacle cups or the urine wells of ovulation tests, would be accurately called in vitro diagnostic medical devices.
"In vitro diagnostic" (IVD) materials may be used in hospital laboratories, doctor's offices, pharmacies, or in some cases (such as store-bought ovulation tests) in the privacy of a patient's own home. The important distinction is that the medical device, substance, or system is reliant on a 'live' human specimen sample, and intended for the investigation (not the treatment or prevention) of a medical condition.
Fingernail clippers are not IVD devices because they do not diagnose any illness, though they may prevent illnesses indirectly by keeping your fingernails short; athlete's foot cream is not an IVD substance, because it treats the common condition of athlete's foot. Ovulation tests are a classic example of an IVD device you might find in someone's home. So, too, a thermometer, a pregnancy test, or a home drug test could be considered an IVD device.
In a simplified manner, IVD substances, devices, and materials offer a way to test for various medical conditions, sometimes from the comfort of one's own home.
How an IVD Test Works
Keeping with the classic example of ovulation tests, let's look at how IVD tests work. In all cases, a 'live' sample from the human body must be supplied. In the case of ovulation tests, this sample is urine. In an insulin meter, another common IVD device, the sample is blood.
The IVD device tests the sample against a parameter. In ovulation tests, the parameter is a specific level of luteinizing hormone (LH). If the LH in the sample is higher than the parameter level, ovulation tests display a double line in the results window of the test. Similarly, the parameter for pregnancy tests is human Chorionic Gonadotropin (hCG). If the level of hCG in the submitted sample is higher than the parameter level recognized by the pregnancy test, its display reflects a positive result: hCG was detected in levels that are above normal, which indicates a possibility of pregnancy.
IVD Accuracy
In a clinical setting, where all variables are carefully considered and controlled, the accuracy of IVD test results is normally quite good. As an example, trained professionals have shown it is possible to get 98% accurate test results on ovulation tests when the directions are followed exactly, but accuracy levels of ovulation tests in reality fall to about 75% due to user error, misinterpretation, or misunderstanding of the directions. The key difference is the willingness and ability to carefully read and follow the directions, exactly as they're written.
With ovulation tests in particular this can prove difficult. Ovulation tests are ongoing, taken daily until positive results are achieved. With a one-time or occasional test, such as a pregnancy test or drug test, accuracy might be improved because the tests are taken less often. Ovulation tests rely on consistent use at the same time of day, every day, for anywhere from seven to twenty-eight days (and, in some cases, even longer). However, accuracy of ovulation tests is not intended to be precise, as some women may experience an LH surge without ovulating, or ovulate without a surge in LH, or skip ovulation in one menstrual cycle completely.
Clinical IVD tests are generally seen as being more accurate, and thus more reliable, than the at-home variants. If you're curious about your ovulation or the chance that you might be pregnant, by all means, try an at-home test; but for results that have a much higher chance of being accurate, you should always consult your doctor.
