• Common causes:
o Bacterial infection
o Inflammation
o Steroids
o Stress
o Myeloproliferative disorders (e.g. CML, PV)
• Left shift: ↑ immature granulocytes (bands, metamyelocytes)
o Seen in infection or marrow stress
• Definition: neutrophils <1.5 × 10⁹/L
• Severe risk: ANC < 0.5 × 10⁹/L → high infection risk
• Causes:
o Viral infections (e.g. EBV, HIV)
o Bone marrow suppression: chemotherapy, radiotherapy
o Aplastic anaemia
o Drugs (e.g. carbimazole, clozapine, sulfasalazine)
o Congenital neutropenia
• Causes:
o Viral infections: EBV, CMV, hepatitis
Atypical lymphocytes: strongly suggest EBV
o Pertussis (whooping cough)
o Chronic lymphocytic leukaemia (CLL)
Smudge cells on blood film
• Causes:
o HIV
o Steroids
o SLE
o Chemotherapy / Radiotherapy
o Severe malnutrition
• Mnemonic — NAACP:
o Neoplasia
o Allergy/Asthma
o Addison’s disease
o Collagen vascular disease (e.g. vasculitis)
o Parasites (especially helminths)
• Causes:
o Chronic myeloid leukaemia (CML) (with eosinophilia and neutrophilia)
o Chronic inflammation
o Allergy
o Hypothyroidism
• Definition: presence of immature myeloid cells + nucleated red cells
• Suggests:
o Bone marrow infiltration: metastatic cancer, myelofibrosis
o Myelophthisis
o Also seen in severe sepsis or haemolysis
• Stepwise approach:
o Differentiate reactive (infection/inflammation) vs malignant (leukaemia/lymphoma) vs marrow failure
• Investigations:
o Blood film: morphology clues
o Infection screen: viral PCR, cultures
o Inflammatory markers: CRP, ESR
o Autoimmune panel: ANA, ENA, dsDNA
o B12, folate (deficiency can affect all lineages)
o Bone marrow biopsy: if persistent unexplained changes or cytopenias
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Author & Educational Disclaimer
Author:
Dr Phillip Cockrell BM FRCP DipClinEd
Dr Phillip Cockrell is a UK Consultant Physician in Internal Medicine, currently working at Queen Alexandra Hospital, Portsmouth University Hospitals NHS Trust. He has previously worked as a registrar across Intensive Care Medicine, Gastroenterology, Cardiology, Stroke Medicine, Acute Medicine, and Respiratory Medicine.
He has held senior leadership roles including Associate Clinical Director of the Acute Medical Unit, Clinical Director of Internal Medicine, and Chief of Medicine. Dr Cockrell has over 15 years’ experience in postgraduate medical education, having lectured extensively across the MRCP syllabus and contributed to MRCP revision teaching and course development.
Dr Cockrell holds a Bachelor of Medicine (BM), Fellowship of the Royal College of Physicians (FRCP), and a Diploma in Clinical Education (DipClinEd). His teaching approach is based on structured consolidation of complex medical topics to support efficient and effective revision for postgraduate examinations.
Purpose of this content:
The material on this page is intended solely for educational purposes to support revision for the MRCP (UK) Part 1 examination. It reflects examination-relevant principles of internal medicine and is designed to aid learning and pattern recognition.
Medical disclaimer:
This content is designed for postgraduate medical examination revision and does not constitute medical advice, diagnosis, or treatment guidance and must not be used as a substitute for professional clinical judgement, local guidelines, or specialist consultation. Clinical decisions should always be made in the context of individual patient circumstances and current national guidance.
