PATHCHAT Edition No. 85
Published: 2023
Please contact your local Ampath pathologist for more information.
Authors:
- Dr. Carissa Chetty
- Dr. Rita Govender
- Dr. Mada Ferreira
Key Messages
✅ Importance of Reference Intervals
- Reference intervals must comply with national and international laboratory standards.
- They should be representative of the South African population, considering racial diversity.
- FBC (Full Blood Count) results should always be interpreted within the context of the patient’s clinical history.
✅ New Reference Intervals Adopted by Ampath
- Implemented in June 2023 to align with current scientific data.
- Based on a South African study conducted in the Western Cape.
- Participants were screened to exclude conditions affecting blood parameters, ensuring accurate reference intervals.
✅ Consultation with a Pathologist
- Persistent, unexplained abnormalities should prompt discussion with a pathologist.
- Pathologists review all FBC results outside reference intervals and assess the need for further testing.
📌 Clinicians should consider clinical presentation, patient history, and prior results when interpreting FBC findings.
Definition of Reference Intervals & Clinical Implications
✅ How Reference Intervals are Defined
- The Clinical and Laboratory Standards Institute (CLSI) defines a reference interval as the range between two reference limits.
- These limits typically represent the central 95% of a healthy population’s test results.
- 5% of healthy individuals may have results outside the reference range.
📌 Abnormal results do not necessarily indicate disease—clinical correlation is essential.
Actionable FBC Results & Diagnostic Cut-Offs
✅ Key FBC Parameters & Their Diagnostic Implications
✔ Anaemia
- Haemoglobin <13 g/dL in men and <12 g/dL in women.
- Previously defined as <10 g/dL in both sexes (WHO 4th edition).
✔ Classification of Anaemia by MCV (Mean Corpuscular Volume)
- Normocytic: 80–100 fL.
- Macrocytic: >100 fL.
- Microcytic: <80 fL.
✔ Polycythaemia
- Haemoglobin >16.5 g/dL (men) or >16.0 g/dL (women).
- Haematocrit >49% (men) or >48% (women).
✔ Leucocyte Abnormalities
- Leucocytosis: WBC ≥11 × 10⁹/L.
- Neutropenia: Absolute neutrophil count <1.8 × 10⁹/L.
- Neutrophilia: Neutrophils >7.5 × 10⁹/L.
- Lymphopenia: Lymphocytes <1.0 × 10⁹/L.
- Lymphocytosis: Lymphocytes >4.0 × 10⁹/L.
- Eosinophilia: Eosinophils ≥0.5 × 10⁹/L.
- Monocytosis: Monocytes ≥1 × 10⁹/L.
✔ Platelet Abnormalities
- Thrombocytopenia: Platelets <150 × 10⁹/L.
- Thrombocytosis: Platelets ≥450 × 10⁹/L.
📌 Persistent, unexplained deviations from these ranges may warrant further investigation for haematological disorders.
Suggested Clinical Actions for Abnormal FBC Results
✅ When to Consider Further Investigation
- Unexplained anaemia, polycythaemia, or cytopenias.
- Symptoms of hyperviscosity (headache, blurred vision, thrombosis risk).
- Febrile neutropenia (urgent medical attention required).
- Persistent thrombocytopenia or thrombocytosis.
✅ Factors Affecting FBC Interpretation
- Pregnancy: Expected increase in MCV.
- Ethnicity: Some individuals of sub-Saharan African descent may have benign ethnic neutropenia.
📌 Pathologists at Ampath review abnormal FBCs and may suggest further investigations when indicated.
Reference Sources & Guidelines Used
✅ Major Sources for Reference Intervals & Haematological Cut-Offs
- WHO 5th Edition (2022) Classification of Haematolymphoid Tumours.
- International Consensus Classification (ICC) of Myeloid Neoplasms & Acute Leukaemias (2022).
- Williams Hematology, 10th Edition (2021).
- Clinical and Laboratory Standards Institute (CLSI) guidelines for reference interval verification.
📌 Ampath’s reference intervals are based on robust, internationally accepted haematology guidelines.
Key Takeaways for Clinicians
✅ FBC interpretation should always consider patient history, symptoms, and previous results.
✅ Ampath’s new reference intervals are locally validated and aligned with international guidelines.
✅ Anaemia, cytopenias, and abnormal white cell counts require further evaluation if persistent or unexplained.
✅ Benign ethnic neutropenia should be considered in appropriate populations before extensive investigations.
✅ Pathologists are available to assist in interpreting abnormal results and advising on additional testing.
📌 Accurate FBC interpretation is essential for diagnosing and managing haematological conditions effectively.