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Question and Answers

Q: We are using tumor markers, some of them for more than 40 years. It is surprising that there are no international quality control programs for them. This is important not only because sometimes the difference between them from one company to the other is more than 20%. You showed clearly some examples with CA 19-9. I have patients whose results with one method were 1000 lg/L, whereas with the other 7 lg/L. We were lucky in that this happened only in 5% of the cases but it was really surprising. We are trying to suggest utilities, cut-offs and algorithms, but the question is who is responsible to help improve this situation? And secondly, what can we do to change that? Sturgeon: I do think that in terms of standardization of the tumor markers and proving things that it is an international exercise where an international organization is required. I believe the IFCC is the best place for that as it can coordinate with the member groups. In terms of looking at an international external quality assessment or proficiency testing that would be a challenge. It sounds like a brilliant idea and we thought about it among European groups of EQA providers but when you actually look at it, it is quite difficult because of the different kinds of philosophies behind external quality assessment in different countries. And then there are practical problems because if you tried to do that internationally, the actual number of samples and material required would be huge. But I do think that there are two things that could be done which are highly desirable. One of them is better communication between EQA providers because we really should be looking to see that the message that comes from, say, the UK is the same as the German scheme or CAP (College of American Pathologists) or where ever else. Although we have tried in the past to increase that communication there has been somewhat limited success, sometime the reports are in different languages etc., etc. It has been suggested that an occasional single distribution, maybe annually, of the same sample by a number of EQA providers, for example in Europe, would be a really interesting thing to do. In principle, it is an international issue. Q: I don’t know if IFCC can do more or not. I will explain one case that I had last week. A patient came with a CA 19-9 result of 500 lg/L from another lab and in my lab the result was 7 lg/L. He asked which the good one is. Am I in good health or not? Sturgeon: I totally agree with you. We don’t know for CA 19-9 which (method) is giving the correct result. We don’t know that for a lot of tumor markers. For the example that you mentioned, it also depends on why the patient was having CA19-9 measured. Did he really have a strong suspicion of pancreatic cancer? We know that many of these tumor markers are raised in many different conditions and are therefore not diagnostic tests. They have to be used carefully and the two really dangerous ones are CA 19-9 and CA125. Q: You mentioned about free light chains being measured in the same laboratory if you can. Similarly, tumor markers should be measured in the same laboratory, if possible, as different assays for a particular tumor marker give different results. If a consultant gastroenterologist were to call you saying that he has a patient with a high CA 19-9 result measured in another lab and ultrasound of the abdomen has shown a mass in the pancreas but your lab has given him a normal CA 19-9 result. How would you answer him? Sturgeon: I would say we had to investigate, that we had to check which method he had got the result from. That should be put into the report from the laboratory. If it were not possible to exchange the sample immediately we would ask for a repeat sample, which should be measured by both methods. And that is where it is important to have a good network of colleagues and colleagues in other laboratories using different methods. In fact, in the UK, we send CA 19-9 samples to referral laboratories and we will ensure that if we are going to change from one laboratory to another we will be very, very careful. Q: I want to make a comment because I do not like to finish in this way. Evidently, techniques are different and the results for the marker from one company to another can be 20% lower or higher. When you compare results obtained from one laboratory with that from the other, the results are so clear that you can make the correct interpretation and decision in the majority of situations. Sturgeon: Yes, I would totally agree and I think that is a very sensible comment. The interpretation depends on the context of the measurement. The laboratory has to change platform occasionally. When we have done that we have always told the clinician we are changing; there may be implications for patients who are being serially monitored.