There are tests to determine whether PCBs are in the blood, body fat, and breast milk. These are not regular or routine clinical tests, butcould be ordered by a doctor to detect PCBs in people exposed to them in the environment and at work. If PCB levels are higher than thebackground levels, this will show that you have been exposed to high levels of PCBs. However, these measurements cannot determine the exactamount or type of PCBs that you have been exposed to, or how long you have been exposed. Although these tests can indicate whether you have beenexposed to PCBs to a greater extent than the general population, they do not predict whether you will develop harmful health effects. Bloodtests are the easiest, safest, and probably the best method for detecting recent exposures to large amounts of PCBs. Results of such testsshould be reviewed and carefully interpreted by physicians with a background in environmental and occupational medicine. Nearly everyone hasbeen exposed to PCBs because they are found throughout the environment, and people are likely to have detectable amounts of PCBs in their blood,fat, and breast milk. Recent studies have shown that PCB levels in tissues from United States population are now declining.