Serum/plasma concentration of **angiotensin II receptor blocker (ARB) metabolites** (specifically, active metabolites of losartan)

Why This Test Might Be Ordered

Your healthcare provider may order this test if you’re taking losartan (a blood pressure medication) and want to ensure it’s working properly. It could also be done if you have kidney problems or if your blood pressure isn’t controlled as expected. Rarely, it may be used to investigate unusual side effects or to check for drug interactions.

What to Expect Before the Test

No special preparation is usually needed. You may have a small needle inserted into a vein (venipuncture) to draw blood. If you’re taking losartan, it’s important to tell your doctor beforehand, as it may affect test results. Avoid eating or drinking for a short time before the blood draw if instructed.

What the Results Mean

This test doesn’t provide a single number like many other blood tests. Instead, it measures the presence and levels of active chemical forms of losartan in your blood. Your doctor will compare these results to your medical history, symptoms, and other test results to determine if your medication is working as intended.

Common Reasons for Monitoring

Healthcare providers may monitor ARB metabolites in cases like kidney disease, where metabolism can be slower. It may also be used if you’re taking other medications that could affect how losartan breaks down in your body.