Trop and CK-MB levels

[aprilleverett]

I'm new to critical care nursing and have a question that the other experienced nurses I work with seemed stumped by:

I had a patient the other night that had a cardiac cath with 4 stent placements in the RCA. Part of the artery was 90% calcified and another part was 70%. After the cath he had chest pain off and on, which was only controlled with 20mcg/hr nitro gtt. His ECG initially showed substantial ST elevation (no big surprise), which resolved over apprx 12 hrs. His cardiac enzymes were quite elevated initially (again, no surprise). So after apprx 24-30 hrs after stent placement his CP subsided and he had been asymptomatic for at least 12 hrs on the nitro which I had slowly titrated down. I drew his cardiac enzymes at that point and his Troponin was elevated by 4 points (from 8 to 12), but his CK-MB was actually lower by over 100 points (however it was still high). What would cause this dissociation between the two levels? Why would one go up and one go down?? I know Troponin is much more reliable, but if it goes up doesn't the CK-MG always go up also - or at least stay at the same level? I can't seem to find any reason in books and articles

[APRN., DNP, RN, APRN, NP]

Perhaps the whacky levels began in the lab? ......As in, the tubes accidently got switched with someone else? (We had a new lab tech not too long ago, and it happens)

[ldybug7]

Stress can cause the trop bump. Afterwards you want to watch the CKMB trend down to make sure there is no issue with the newly placed stents. It also takes about 24 hours for the trop to peak after the MI. It probably was just peaking.

[Ranier]

These markers have different kinetics. CPK peaks within a few hours and then declines relatively rapidly. Troponin takes about 24 hours to peak and then days to decline. So you were probably testing in that window between the two peaks- CPK was already on the way down and troponin was still rising. This would happen within a roughly 12-24 hour window post-event, which seems to fit your scenario.

[in2bate71, BSN, RN]

http://en.wikipedia.org/wiki/Cardiac_marker

[Rook]

I'm a chem/hematology lab tech and a RN. CK-MBs aren't considered a good cardiac marker anymore and many hospitals including the one I work at don't use them anymore. AST and LH are also considered to not be good cardiac markers as well.

If you are thinking its an error though do a redraw. The machines are almost always accurate however cardiac markers can have a error if you use serum tubes to collect them (I don't know why many hosp collect card markers in serum tubes) and the patient is on heparin and/or other anticoagulants. Because even after sitting for 1hr you could get a fibrin clot in the serum and sometimes the machine doesn't flag it during sampling.

[aCRNAhopeful]

That is an expected result. Just as Ranier said. Look at the curves of the rise, peak, fall of the different cardiac enzymes. That's why we never check a troponin after an MI and PCI, it doesn't really tell you anything. We do trends of a plain old CK because we know it should be trending down rather quickly. It is not cardiac specific so if the patient had major bodily trauma then of course it wouldnt be accurate. However the majority of the time the only muscle that's injured is the heart and if the CK levels are dropping then you know that there is no active event going on. If a plain old CK level is negative, then the patient hasn't had an MI.

And why monitor the troponin levels after an MI anyways? You already know that there going to be elevated and does it matter if it says 4, 5, 80, or 1000? In that case what they need is an echo or some other similar study to tell you how bad the MI was and what kind of function they have left now.