There are no direct tests of detoxification capacity.  Indirect tests only measure a few of the thousands of processes involved in detoxification.  The most popular and useful of these tests involves ingesting three compounds, caffeine, acetaminophen, and acetylsalicylic acid. . Saliva and urine are analyzed for metabolites of the three compounds to determine how well the liver can convert and clear toxins from the body in the most commonly used phase I and phase II processes. This test is only accurate in adults.  This test is considered experimental and is not covered by insurance.

Another indirect way to examining detoxification capacity is with the ION Profile, which examines blood and urine for many substances.  Again, we are using a proxy.  In this test, substances appear in the urine or blood in greater quantities if the body is not properly detoxifying.  Rather than directly measuring detox activity, we measure the chemicals that accumulate when the detoxification activity is impaired.  This test is approved, but has not been subjected to clinical trials and is not covered by most insurers.

How to assess your detoxification capacity
A Simple Safe detox program
Further information links
Can nutrition affect chemical toxicity?