Lipase vs Amylase & Troponin vs CK?

Question

Where I come from Troponin is used instead of CK, as its prolonged raise seems to be more useful than CK, and all CK seems to do is let us know that a MI just occured, (in which case we would already be treating as symptomatic MI.)

Also Lipase is more sen and spec than Amylase - yet alot of drs order amylase for pancreatitis / etc... Why is this?

If any1 knows any extra info on the above/insights would love to hear from you

thanks

Answer 1

Troponin and CK both have their uses, but Troponin alone is almost 100% diagnostic - CK is not. You have to also bear in mind that the blood tests are only one part of the clinical picture.

You might already know all this but here's what I know...

The advantages of CK are that it rises fast after an MI (within a few hours). It is also simple to measure - the measurement uses a straighforward chemical reaction, which is simple and cheap and can be done on a routine chemistry analyser. CK is a sensitive marker - it will be raised in the vast majority of people who have had an MI. The disadvantage is that it's not specific - any kind of muscle damage anywhere in the body will raise CK - eg a fall, an injury, muscle inflammation, effects of statins, etc etc. It also varies between ethnic groups and with the amount of exercise a person does. CK falls within a couple of days after the event, so it is a good marker for re-infarction but no good for late presenters. .

Troponin doesn't rise very fast after an MI and the best evidence base for its use as a cardiac marker is from results 12 hours after the patient has been admitted to hospital. Troponin can be measured by a simple automated analyser, but it has to be measured by immunoassay - using antibodies. This is a more complicated method, may take longer than routine chemistry and costs much more.

However, the advantages far outweigh this. Troponin (T or I) are components of all muscles, but they have cardiac-specific forms, so raised cardiac troponin means there has specifically been cardiac muscle damage - it is incredibly specific. Obviously this could be from cardiac surgery, infection, defibrillation, etc, but those are things that you would know about. Troponins are also extremely sensitive - at 12 hours after an event, very close to 100% of people who had an MI will have raised troponin and very close to 100% of people who didn't have an MI will have normal troponin. The method used to measure Troponin T (rather than Trop I) is patented by one company and the precision and sensitivity is amazing - you can detect very small elevations in people with unstable angina but no MI. The fact that Trops remain elevated for up to 2 weeks is good for late presenters but no good to detect re-infarction.

So they both have their uses - CK is good in the acute setting but not very specific. Troponin can be used for rapid rule-in (but an early negative result does not exclude MI), or later rule-out.

As for amylase and lipase - I don't know so much about this but I don't think there's a great deal of difference between them - I think either can be used.

edit: forgot to mention CKMB but I think it's becoming outdated now we have troponins.

Answer 2

Well, CK-MB rises first, so if you get a patient early in an MI, troponin levels may still be normal. If you didn't order a CK-MB, you would have just the EKG to differentiate angina vs. MI vs. numerous other causes of chest pain. Where I come from we order both.

As to the pancreatic enzymes, I am not sure on  the specifics of that, but a lot of Dr's can't keep up on 100% of changes in a medical field. I mean just on here I would say over half of the docs give advice on blood pressure meds that aren't current with JNC-7, especially if it falls outside their specialty. Others just like to do things the way they always have.