hGH & CK-MB: Biomarker Guide – Physiology, Clinical Indications & Interpretation
Human Growth Hormone (hGH) and Creatine Kinase-MB (CK-MB) are distinct biomarkers for growth/metabolism and cardiac injury, respectively.
1. Human Growth Hormone (hGH / Somatotropin)
| Aspect | Details |
|---|
| Source | Anterior pituitary somatotrophs |
| Regulation | GHRH (stimulates), Somatostatin (inhibits), Ghrelin (stimulates), IGF-1 negative feedback |
| Secretion Pattern | Pulsatile; peak during slow-wave sleep; higher in puberty; declines with age |
| Actions | Linear growth (via hepatic IGF-1), lipolysis, protein synthesis, gluconeogenesis, immune modulation |
| Clinical Indications | Growth failure evaluation; acromegaly/gigantism diagnosis; GH deficiency (adult/pediatric); pituitary tumor monitoring |
| Testing | Stimulation tests (insulin tolerance, arginine, clonidine, glucagon) for deficiency; Suppression test (OGTT) for acromegaly. Random hGH unreliable due to pulsatility. |
| IGF-1 | Stable surrogate; integrates pulsatile GH. First-line screening for acromegaly/GHD. |
2. Creatine Kinase-MB (CK-MB)
| Aspect | Details |
|---|
| Source | Cardiac myocytes (≈15–30% of total CK in heart; <5% in skeletal muscle) |
| Isoforms | CK-MB2 (tissue) → CK-MB1 (plasma); MB2/MB1 ratio >1.5 = early MI marker |
| Kinetics Post-MI | Rises 3–6 hr; peaks 12–24 hr; normalizes 48–72 hr. Earlier & more cardiac-specific than total CK. |
| Clinical Indications | Early MI diagnosis (serial q6–8h ×24h); reperfusion success (early peak); reinfarction (recurrent rise); periprocedural MI (PCI/CABG) |
| Limitations | Elevated in: skeletal muscle trauma, rhabdomyolysis, myositis, heavy exercise, renal failure, hypothyroidism. Superseded by cardiac troponin (cTnI/T) as preferred biomarker. |
| Current Role | Periprocedural MI definition (PCI: >5×URL; CABG: >10×URL); early reinfarction detection; troponin-unavailable settings. |
Key Contrasts
| Feature | hGH | CK-MB |
|---|
| Primary System | Endocrine / Growth | Cardiovascular / Injury |
| Sample | Serum (fasting, timed) | Serum/Plasma (serial) |
| Dynamic Testing | Essential (stim/suppress) | Serial kinetic interpretation |
| Gold Standard Replacement | IGF-1 for screening | Cardiac Troponin for MI |
Both remain valuable in specific niches despite newer markers. Understanding their physiology, kinetics, and limitations prevents misinterpretation.
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