therapeutic-drug-monitoring
Reviewed
Also called: medicine levels blood test, therapeutic drug levels
Therapeutic drug monitoring (TDM) measures the amount of certain medicines in your blood to check whether the dose is safe and effective. It helps your provider determine the right dose for medicines that must stay within a specific range in your blood to work well and avoid dangerous side effects.
Specimen: blood
Why this test may be ordered
- To determine the most effective dose when you first start taking a medicine that requires close monitoring.
- To regularly check that the medicine level remains effective and safe over time, especially if your health, other medicines, or age change.
- To check if you have symptoms of a serious side effect from the medicine.
- To make sure you are taking your medicine as prescribed.
Preparation and collection
Depending on the type of medicine you are taking, you may need to schedule your test before or after taking your regular dose. Tell your provider about any other medicines or supplements you take, as they may affect the results.
A health care professional will take a blood sample from a vein in your arm using a small needle. The procedure usually takes less than five minutes.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Understanding results
Your results will show if medicine levels in your blood are in a range that is medically helpful but not dangerous. This is called the 'therapeutic range.' The range varies depending on the type of medicine and your own health needs.
- Medicine level within the therapeutic range: The amount of medicine in your blood is at a level that is considered safe and effective for your condition. Limitation: The therapeutic range varies by medicine and individual health needs. Your provider will interpret the result based on your specific situation. Next step: Routine
- Medicine level outside the therapeutic range (too low or too high): The amount of medicine in your blood may be too low to be effective or too high, which could be unsafe (toxicity). Limitation: The result does not diagnose a condition; it indicates that your dose may need adjustment. Many factors (aging, pregnancy, illness, infection, other medicines) can affect medicine levels. Next step: Prompt
- The therapeutic range varies depending on the type of medicine and your own health needs.
- Many factors such as aging, pregnancy, illness, infection, and other medicines can affect how quickly your body processes the medicine, leading to changes in blood levels.
- Results are interpreted by your healthcare provider, who will adjust your dosage as needed.
What to do next
If your results are not in the therapeutic range, your provider may need to adjust your dosages. If your dosages change, you may get repeated tests until your medicine levels fall into the therapeutic range. Talk to your provider if you have questions about your results.
- What is my specific therapeutic range for this medicine?
- How often should I have this test?
- What symptoms of side effects should I watch for?
- Do any of my other medicines or supplements affect the results?
Evidence source
U.S. National Library of Medicine: therapeutic-drug-monitoring