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Leukocyte alkaline phosphatase
🧪 Leukocyte Alkaline Phosphatase (LAP) is an enzyme found in neutrophils. The LAP score (0–400) is used as a diagnostic aid in distinguishing between reactive vs malignant myeloproliferative processes.
📈 Conditions where LAP is Raised
- 🌲 Myelofibrosis
- ⚡ Leukemoid reactions (marked neutrophilia due to infection or stress)
- 🩸 Polycythaemia rubra vera
- 🦠 Severe infections
- 💊 Steroid therapy, Cushing’s syndrome
- 🤰 Pregnancy or OCP use
📉 Conditions where LAP is Low
- 🧬 Chronic Myeloid Leukaemia (CML) ❗ (classic exam point)
- 🩺 Pernicious anaemia
- 🌙 Paroxysmal nocturnal haemoglobinuria (PNH)
- 🤒 Infectious mononucleosis
🧠 Exam Tip
- 👉 LAP ↑ in reactive states (e.g. infection, myeloproliferative disorders).
- 👉 LAP ↓ in CML – a key differentiator from a leukemoid reaction.
🧪 Leukocyte Alkaline Phosphatase (LAP) is a useful tool in differentiating between a Leukemoid Reaction (benign/reactive) and Chronic Myeloid Leukaemia (CML).
🔎 Leukemoid Reaction vs CML
| Feature | Leukemoid Reaction ⚡ (Reactive) | CML 🧬 (Malignant) |
|---|---|---|
| Cause | Infection, stress, haemorrhage | BCR-ABL fusion gene (Philadelphia chromosome) |
| WCC | Raised, usually < 50 × 10⁹/L | Very high, often > 100 × 10⁹/L |
| Cells | ↑ Neutrophils with toxic granulation | All myeloid stages: myeloblasts → mature neutrophils |
| LAP score | 📈 High (reactive neutrophils) | 📉 Low (clonal defect in CML) |
| Spleen | Usually normal | Splenomegaly common |
| Genetics | None | Philadelphia chromosome t(9;22) present |
🧠 Exam Tip
- LAP is the key discriminator: ⬆️ in leukemoid reaction, ⬇️ in CML.
- If you see very high WCC + splenomegaly + low LAP → think CML.
- Always confirm CML with cytogenetics (Philadelphia chromosome).
| The content on this website is provided for educational and informational purposes only to support exam preparation (e.g., MLA, MRCP, USMLE) and learning. This is NOT medical advice, diagnosis, treatment, or professional guidance. It does not replace consultation with a qualified healthcare professional, official guidelines (e.g., NICE, GMC, BNF), or supervised clinical practice. Always verify information with current, authoritative sources. Makindo and its contributors accept no liability for any reliance on this content, including errors, omissions, or any resulting harm, loss, or consequences. By using this site, you agree to these terms. |
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