Enzyme diagnostics can be used to detect cardiac muscle-specific isoenzymes in blood serum that are present in elevated concentrations after myocardial infarction. 1st-order laboratory parameters-obligatory laboratory tests.
- Myoglobin – early diagnosis or exclusion of myocardial necrosis (cell death of the heart muscle) in acute coronary syndrome (ACS).
- Troponin T (TnT) – high cardiospecificity with high sensitivity (percentage of diseased patients in whom the disease is detected by use of the test, i.e., a positive test result occurs; also allows differentiation between NSTEMI (NSTE-ACS) and unstable angina):
- For the high-sensitivity troponin test (hs-cTnT), a second measurement should be performed as early as after 3 hours (“3-hour exclusion protocol”) in case of initially inconclusive values; recommendation for ESC 0/3h algorithm downgraded from class I to class IIa. Currently git: the second measurement should be made as early as after 1 hour (“1-hour exclusion protocol”; ESC 0/1h rule-out/in algorithm) [Guidelines: ESC Guidelines].
- If NSTEMI is suspected, a second hs-troponin determination should be performed as early as after 1 hour (1-hour rule-in/out algorithm). [Very low hs-troponins at initial determination + low values without detectable variations at second measurement → negative predictive value for acute myocardial infarction > 98%]
- Creatine phosphokinase (CK), especially isoenzyme MB (CK-MB).
- Aspartate aminotransferase (AST, GOT).
- Lactate dehydrogenase (LDH)
- Hydroxybutyrate dehydrogenase (HBDH)
- Uric acid – strong independent predictor (predictive value) of mortality (mortality).
- Small blood count [leukocytosis – increase in white blood cells]
- Inflammatory parameters – CRP (C-reactive protein) or ESR (erythrocyte sedimentation rate) [increased].
- Fasting glucose (fasting blood glucose) – due toexclusion of hyperglycemia (increased concentration of glucose in the blood).
- Albumin in the urine [microalbuminuria and condition after myocardial infarction → a factor of 2-4 increased risk of suffering another infarction or even cardiovascular death]
| Parameter | Increase (after infarct onset) | Maximum (after infarct onset) | Normalization (after infarct onset) | Notes on specificity, etc. |
| Myoglobin | 2 – 6 h | 6 – 12 h | 1 d |
|
| Troponin T (TnT) | 3 – 8 h | 12 – 96 h | 2 weeks |
|
| CK-MB | 3 – 12 h | 12 – 24 h | 2 – 3 d |
|
| CK | 3 (-4) – 12 h | 12 – 24 h | 3 – 6 d |
|
| GOT | 6 – 12 h | 18 – 36 h | 3 – 6 d |
|
| LDH | 6 – 12 h | 48 – 144 h | 7 – 15 d | |
| HBDH | 6 – 12 h | 48 – 144 h | 10 – 20 d |
Clinical Chemistry Score (CCS) for calculating the probability of myocardial infarction.
Using the CCS, in emergency department patients with ACS symptoms, it is possible to classify patients who are at low risk for unstable angina, myocardial infarction, and death and therefore can be discharged home.
| Laboratory parameters | Points | ||
| Glucose in serum | |||
| <5.6 mmol/L | < 100.9 mg/dL | 0 | |
| ≥ 5.6 mmol/L | ≥ 100.9 mg/dL | 1 | |
| eGFR | |||
| < 90 mL/min/1.73 m2 | 1 | ||
| ≥ 90 mL/min/1.73 m2 | 0 | ||
| hs-cTnT/hs-cTnI | |||
| hs-cTnT < 8 ng/L | 0 | ||
| hs-cTnI 8-18 ng/L | 1 | ||
| hs-cTnI 19-30 ng/L | 2 | ||
| hs-cTnI > 30 ng/L | 3 | ||
The primary study end point-myocardial infarction or death within 30 days-occurred in 17.1 percent. Interpretation:
- CCS: 0 points, only 1 of 4,245 patients was affected by the primary end point; sensitivity was 100% for the primary end point, ie, there were no false-negative results
- CCS: 5 points; depending on the cohort, between 50% and 90% were affected by the primary endpoint; approximately 10% of patients are expected to have 5 points; specificity was 96.6% with a positive predictive value (PPV) of 75.1% for hs-cTnI and 94% with a PPV of 61.7% for hs-cTnT
Legend
- EGFR: engl.estimated GFR, i.e. the estimated glomerular filtration rate (here: calculated according to the CKD-EPI creatinine formula).
- Hs-cTnl: engl. high-sensitive cardiac troponin, i.e. high-sensitive cardiac troponin.
Further notes
- Differentiating type 1 myocardial infarction (T1MI) without ST elevation (NSTEMI) from type 2 myocardial infarction (T2MI) is clinically difficult. Patients with T1MI are more likely to have a retrosternal (“behind the sternum“) feeling of pressure or oppressive chest pain (chest pain) and pain in the left shoulder and arm. Patients with T2MI are more likely to complain of vertigo (dizziness) and lightheadedness, as well as dyspnea (shortness of breath).For the definition of a type 1 or type 2 myocardial infarction, see Classification below.
- In the T2MI group, due to cardiac wall stress, the release of natriuretic peptide is increased: Researchers demonstrated that natriuretic peptide levels (measured as NT-proBNP) were significantly higher in the T2MI group at all times (30 and 60 minutes) except after three hours. The T!MI patients always had higher levels of cardiac troponin (measured as cTnT gene 5); however, they were not significantly higher than in the T2MI patients. The quotient of both values: NT-proBNP/cTnT gene 5 showed a significantly higher value for patients with T2MI at all measurement points.
Preventive laboratory diagnostics
- Ceramides (in plasma) – to predict cardiovascular risk [currently still in the trial phase].
- Lp-PLA2 (vascular inflammatory enzyme lipoprotein-associated phospholipase A2; inflammatory marker) – for risk stratification of cardiovascular disease.
- MICRA (Myocardial Infarction-associated Circular RnA) – prognostic indication of whether an affected person will develop heart failure after a myocardial infarction.
