Firstly, CEA, is a tumor marker test that falls under the catagory of immunoassay testing. Each manufacturer of the instruments to perform this test develop their own method for the testing. Immunoassay instruments often do not correlate from one method to another (what may be 45 on one instrument and method, might be 55 on another instrument/method). It is important that people who are having serial tumor marker testing performed, have it done at the same place for the duration of the monitoring period to insure the most consistant results.
There are two ranges that are determined in any Laboratory test. The analytical range (AMR) and the clinically reportable range (CRR). The AMR, is the span of both minimum and maximum range that the instrument performing the test can analyze. The CRR is the maximum value that the laboratory determines to be clinically significant to patient diagnosis, beyond which obtaining a "number" is no longer useful. In the case of CEA, for example, lets say the instrument can measure CEA as low as 0.1 and as high as 100. Once the test exceeds the value of 100, the patient's specimen must then be diluted to obtain the result. The laboratory will continue to dilute the specimen until they reach the maximum value that is clinically useful for diagnosis. This value varies from Laboratory to Laboratory, and test to test, and is determined by the Laboratory's Medical Director. So, in one laboratory, they may be willing to dilute the specimen until they eventually report ">500" and at another laboratory they may continue to dilute the specimen until it is ">5000". At some point, obtaining the "number" becomes irrelavent, because it will not change the physician's course of treatment nor will it further the physician's diagnosis.
There can be some correlation between tumor marker values and treatment, but what the immediate course of action, after a single increase would be, is up to the physician monitoring the patient.
Medical Technologist, 20 years of experience in Laboratory Medicine, Core Lab Manager of a Hospital Laboratory
· 1 decade ago