Basic Approach to Abnormal FBC (Part 2): Platelets and White Blood Cells

by Dr. Carol Moore, MBChB (UCT), MMed in Haematopathology (University of Stellenbosch)

PATHCHAT Edition No. 9: Part 2
Please contact your local Ampath pathologist for more information.

PLATELETS

Important Considerations:

• Platelet counts are generally higher in women.
• Individuals of African descent tend to have lower platelet counts than those of Caucasian descent.

Thrombocytopenia (Low Platelet Count)

🔹 Step 1: Exclude Pseudo-Thrombocytopenia

• A false low platelet count can occur due to:
  • Difficult venepuncture.
  • EDTA-induced platelet clumping (repeat platelet count using a sodium citrate tube).
• Confirm thrombocytopenia by examining a peripheral blood (PB) smear or repeating the count.

🔹 Step 2: Identify Serious Causes Requiring Urgent Treatment

• Consider thrombotic thrombocytopenic purpura (TTP), haemolytic-uraemic syndrome (HUS), or disseminated intravascular coagulation (DIC).
• Recommended tests:
  • Lactate dehydrogenase (LDH), bilirubin, urea & electrolytes (U&E), and DIC screen.
  • PB smear review for platelet fragments.

🔹 Step 3: Consider Common Causes

• Drug-induced thrombocytopenia (e.g., antibiotics, thiazide diuretics, heparin).
• Viral infections (HIV, other viral illnesses).
• Autoimmune conditions (systemic lupus erythematosus (SLE)).
• Liver disease & hypersplenism.
• Recommended tests:
  • HIV serology, antinuclear factor (ANF), liver function tests (LFTs), and abdominal ultrasound.

🔹 Step 4: Consider Idiopathic Thrombocytopenic Purpura (ITP)

• If all the above causes are excluded, ITP is a likely cause.
• If clinical findings are inconsistent with ITP, consider a bone marrow biopsy to assess for:
  • Myelodysplastic syndrome (MDS).
  • Lymphoproliferative disorders.

Thrombocytosis (High Platelet Count)

🔹 Step 1: Differentiate Between Primary (Malignant) and Secondary (Reactive) Causes

• Primary thrombocytosis (malignant) → Associated with increased risk of thrombosis or bleeding.
• Secondary thrombocytosis (reactive) → Often due to:
  • Infection or inflammation.
  • Pregnancy.
  • Iron deficiency.
  • Malignancies.
  • Post-splenectomy state.
• Patient history and examination are crucial for differentiating between these causes.

🔹 Step 2: Initial Investigations for Reactive Causes

• Ferritin (to check for iron deficiency).
• C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) (to assess for inflammation).
• Peripheral blood (PB) smear review.

🔹 Step 3: Consider Myeloproliferative Disorders

• If no reactive cause is found, consider primary thrombocytosis.
• Recommended tests:
  • JAK2 PCR (to detect polycythaemia vera or essential thrombocythemia).
  • Fluorescence in situ hybridisation (FISH) for BCR/ABL (to assess for chronic myeloid leukaemia (CML)).
  • Bone marrow biopsy if primary disorder is suspected.

WHITE BLOOD CELLS (WBCs)

🔹 Different Types of WBC Abnormalities:

• Neutropenia (low neutrophil count).
• Neutrophilia (high neutrophil count).
• Lymphocytosis (high lymphocyte count).
• Lymphopenia (low lymphocyte count).
• Monocytosis (high monocyte count).
• Eosinophilia (high eosinophil count).
• Basophilia (high basophil count).

Neutropenia (Low Neutrophil Count)

🔹 Step 1: Identify Acquired vs. Congenital Causes

• Severe neutropenia (<0.5 × 10⁹/L) → High risk for infection.
• Common acquired causes:
  • Drugs (antibiotics, NSAIDs, anticonvulsants, immunosuppressants, antipsychotics).
  • Infections (especially viral infections like HIV).
  • Autoimmune diseases (e.g., lupus-related immune neutropenia).
  • Haematological malignancies (e.g., myelodysplastic syndromes (MDS)).

🔹 Step 2: Recommended Investigations

• Stop suspected drug & monitor FBC.
• HIV testing if indicated.
• B12 and folate levels, LFTs, serum protein electrophoresis.
• Antinuclear factor (ANF) and rheumatoid factor (RF) (to assess autoimmune causes).

🔹 Step 3: Consider Haematological Referral If:

• Severe neutropenia (<0.5 × 10⁹/L).
• Lymphadenopathy, hepatosplenomegaly, or persistent/progressive neutropenia >6 weeks.

Neutrophilia (High Neutrophil Count)

🔹 Step 1: Differentiate Between Reactive vs. Malignant Causes

• Reactive neutrophilia:
  • Infection (especially bacterial infections).
  • Inflammation, malignancy, pregnancy, smoking, strenuous exercise.
  • Drug-induced (steroids, adrenaline).
• Malignant causes:
  • Chronic myelogenous leukaemia (CML).

🔹 Step 2: Recommended Investigations

• Peripheral blood smear to check for blasts or leukoerythroblastic reaction.
• FISH for BCR/ABL if malignancy suspected.

Lymphocytosis (High Lymphocyte Count)

🔹 Step 1: Review Peripheral Blood Smear

• Reactive lymphocytosis (e.g., viral infections like EBV, CMV, HIV).
• Persistent lymphocytosis (>4-6 weeks):
  • Consider chronic lymphocytic leukaemia (CLL).
  • Perform immunophenotypic analysis via flow cytometry.

🔹 Step 2: Consider Additional Testing If:

• Lymphadenopathy, splenomegaly, weight loss, or hepatomegaly present.
• Lymphocyte morphology is abnormal.

Monocytosis, Eosinophilia & Basophilia

🔹 Monocytosis (High Monocyte Count)

• Reactive causes: Chronic infections, inflammatory/granulomatous diseases, metastatic cancer.
• Persistent monocytosis (>1.5 × 10⁹/L): Consider myeloproliferative disorders → Bone marrow biopsy + cytogenetic studies.

🔹 Eosinophilia (High Eosinophil Count)

• Reactive causes: Parasites, allergies, asthma, drug reactions, autoimmune diseases.
• Primary eosinophilia: Consider hypereosinophilic syndrome or haematological malignancy → Bone marrow biopsy + genetic testing.

🔹 Basophilia (High Basophil Count)

• Rare, usually linked to myeloid malignancies.
• Requires bone marrow examination & haematological referral.