Choice and evaluation of clinical laboratory parameters in myocardial diseases.
Troponin (reference range 0.00-0.06 μg/l and in acute MI>40 μg/l)
a protein which regulates the muscle contraction. Controls the interaction of actin, myosin and the level of intracellular ionized calcium.
It has 3 complexes:
- ТrТ (structural protein), bounds the troponin complex with the molecules of tropomyosin
- ТrС (has 4 binding sites for Са++). Identical in the myocardial and skeletal muscles
- ТrI (protein inhibitor, activates actin-myosin-ATP-аse)
High diagnostic specificity – 98% for acute MI Broad diagnostic window (from 10 h to 10 days). Available fast immunoenzyme methods with high analytical reliability
Elevated in myocardial infraction two phases:
I phase – starts 2.-3. h after the ischemia and lasts to 4-6 days
II phase – starts 3.-4. days after the ischemia and lasts 5-8 to 10 days after it.
Creatine Phosphate: Reference range: Total CK: Male 25 – 200 U/l; Female 25 – 175 U/l CK-MB up to 20 U/l. Elevated 10x in myocardial infraction
Determination of the isoforms CК-МВ2 and CК-ММ3 after acute myocardial infarction is very important for distinguishing the presence and the lack of reperfusion of the affected region of the myocardium. When the perfusion is restored, the activity of the tissue isoforms in the serum is greatly increased, because of the so called „wash-out effect”. The lack of reperfusion points unsuccessful thrombolytic therapy and urgent surgery intervention should be done.
Myoglobin: Is a sensitive early marker, cheap to analyse and can be detected in the urine. Myoglobin increases as soon as 1 to 3 hours after symptom onset in AMI (acute myocardial infraction). The change in myoglobin may help identify acute myocardial infraction in patients with normal cardiac levels of troponin I on admission
Glycogen Phosphorylase BB: Specific for myocardium Early elevation - 2-3 h after AMI and no change in lesions of skeletal muscles. Disadvantages: very high sensitivity raises in stable angina pectoris, some methodological problems
Late markers include LDH and ASAT:
LDH (230 – 460 U/l) elevated after 12-14 hours and levels are 5-10x higher in myocardial infraction. It goes back to normal in 12-14 days.
ASAT (ASAT 0 – 36 U/l) elevated after 8-12 hours and goes back to normal in 7-8 days. levels are 5-10x higher in myocardial infraction
Non-enzymes tests include:
- Erythrocyte sedimentation rate elevated after 15-20 hours last 10-14 days
- Leucocytosis, Neo with left shift after 3 hours
- Hyperglycaemia after 2 hours