Isoenzymes: Clinical Distinctions
Isoenzymes (or isozymes) are different physical forms of the same enzyme that catalyze the same chemical reaction but are encoded by different genes and have different kinetic properties, tissue distributions, or regulatory mechanisms.
| Enzyme | Key Isoenzymes | Clinical Utility |
|---|---|---|
| LDH | LDH-1 to LDH-5 | LDH-1 (Heart/RBCs),
LDH-5 (Liver/Skeletal muscle). LDH-1 > LDH-2 suggests MI. |
| CK (Creatine Kinase) | CK-BB, CK-MB, CK-MM | CK-MB is highly sensitive to myocardial injury.
CK-MM indicates skeletal muscle. |
| Alkaline Phosphatase | Bone, Liver, Placental | Distinguishes between liver pathology and bone turnover (e.g., Paget disease). |
High-Yield Core Realities:
- Tissue Specificity: Isoenzymes allow clinicians to pinpoint the source of organ damage by identifying which tissue-specific form of an enzyme is leaking into the serum.
- Diagnostic Accuracy: While less critical with the advent of specific biomarkers like Cardiac Troponins, understanding isoenzymes remains fundamental for interpreting laboratory profiles and organ-specific pathology.