## Biochemical Markers in Protein-Energy Malnutrition **Key Point:** Serum prealbumin (transthyretin) is the most sensitive and specific marker for protein malnutrition because of its short half-life (2–3 days) and rapid response to nutritional repletion. ### Comparison of Protein Markers | Marker | Half-life | Sensitivity | Specificity | Clinical Use | |--------|-----------|-------------|-------------|---------------| | **Prealbumin (Transthyretin)** | 2–3 days | High | High | **Gold standard for protein status** | | Serum albumin | 20 days | Moderate | Low | Chronic malnutrition; affected by liver disease, inflammation | | Total serum protein | Variable | Low | Low | Non-specific; includes globulins | | BUN | Variable | Low | Low | Reflects renal function, not protein status | **High-Yield:** Prealbumin levels: - Normal: 20–40 mg/dL - Mild depletion: 15–20 mg/dL - Moderate depletion: 10–15 mg/dL - Severe depletion: <10 mg/dL **Clinical Pearl:** Serum albumin is a poor acute marker because its long half-life (20 days) means it reflects chronic nutritional status. Prealbumin rises within 3–5 days of adequate protein intake, making it ideal for monitoring nutritional intervention response. **Warning:** Both albumin and prealbumin are negative acute-phase reactants and may be falsely low in acute inflammation, sepsis, or liver disease—independent of protein malnutrition.
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