Blood Count — Complete Blood Evaluation

A full blood count quantifies the cellular components of peripheral blood through automated haematology analysers. The analysis evaluates three primary cell lineages: erythrocytes (red blood cells), which carry oxygen via haemoglobin; leukocytes (white blood cells), which orchestrate immune defense; and thrombocytes (platelets), which facilitate haemostasis and vascular repair. The test also calculates indices like haematocrit, mean corpuscular volume, and the white cell differential count, detailing neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

In oncological practice, the bone marrow is exceptionally vulnerable to both malignant infiltration and the cytotoxic mechanisms of antineoplastic therapies. Systemic chemotherapy, targeted agents, and radiotherapy suppress rapidly dividing haematopoietic precursors, causing transient or prolonged reductions in blood cell populations. Consequently, the blood count acts as a dynamic surrogate measure of bone marrow reserve and systemic physiological recovery.

Cancer therapies can induce myelosuppression, leaving patients susceptible to debilitating anaemia, spontaneous bleeding, or life-threatening infections such as neutropenic sepsis. Regular blood counts alert medical teams to clinically silent declines in cell numbers before symptoms escalate. Clinicians depend on blood count metrics to calculate safe drug dosages, determine whether to temporarily pause or reduce systemic treatments, and decide when supportive interventions, such as blood transfusions or granulocyte colony-stimulating factors, are warranted.

A blood count is conducted on a standard venous blood sample collected in an ethylenediaminetetraacetic acid (EDTA) tube. Automated analysers generate quantitative values, including absolute neutrophil count (ANC), haemoglobin concentration, and platelet count. If abnormal cell populations or flags are detected, a haematologist examines a stained peripheral blood smear under a microscope.

Blood counts are standard across all cancer types. They are especially critical in haematological cancers such as leukaemia, lymphoma, and multiple myeloma, and in solid tumours treated with cytotoxic chemotherapy, including breast, colorectal, ovarian, and lung cancers. They are also monitored in patients undergoing pelvic radiotherapy or extensive bone-directed therapies.

Specific thresholds are mandated before proceeding with cytotoxic chemotherapy; typically, an ANC of at least 1.0–1.5 × 10⁹/L and platelets above 75–100 × 10⁹/L are required. Substantial cytopenias prompt dose delays, dose reductions, or supportive treatments such as filgrastim (G-CSF) injections, erythropoiesis-stimulating agents, packed red cell infusions, or platelet transfusions.