Full Blood Count (FBC/CBC): The Complete Guide
The most commonly ordered blood test in the world -- measuring red cells, white cells, and platelets to reveal how your blood is performing.
What is a Full Blood Count?
A Full Blood Count (FBC) -- called a Complete Blood Count (CBC) in the United States -- is the most frequently ordered blood test worldwide. It measures the three main types of cells circulating in your blood: red blood cells that carry oxygen, white blood cells that fight infection, and platelets that control bleeding.
A single FBC test produces approximately 15 individual results, giving your doctor a comprehensive snapshot of your blood health. It is routinely ordered as part of annual checkups, pre-surgical assessments, fatigue investigations, and infection monitoring. Understanding what each number means helps you have more informed conversations with your healthcare provider.
The Three Blood Cell Families
Your blood contains three families of cells, each with a distinct role. Every FBC result maps back to one of these three groups.
Red Blood Cells
Your oxygen delivery system
Haemoglobin (Hb)
The oxygen-carrying protein inside red cells. The single most important indicator of anaemia.
Red Blood Cell Count (RBC)
Total number of red cells per litre of blood. Low counts confirm anaemia; high counts may indicate polycythaemia.
Haematocrit (Hct/PCV)
The percentage of blood volume occupied by red cells. Reflects hydration status and red cell mass.
MCV (Mean Cell Volume)
Average size of each red cell. Key to classifying anaemia as microcytic, normocytic, or macrocytic.
MCH (Mean Cell Haemoglobin)
Average weight of haemoglobin per red cell. Parallels MCV -- low MCH usually accompanies low MCV.
MCHC (Mean Cell Hb Concentration)
How densely packed with haemoglobin each cell is. Low in iron deficiency, raised in spherocytosis.
RDW (Red Cell Distribution Width)
Measures variation in red cell size. High RDW signals mixed cell populations (anisocytosis).
White Blood Cells
Your immune army
Total WBC Count
Combined count of all white cell types. High in infection or inflammation; low in immune suppression.
Neutrophils
First responders to bacterial infection. Make up 60-70% of white cells. Rise sharply during acute infections.
Lymphocytes
Include B-cells (antibodies) and T-cells (cell-mediated immunity). Rise in viral infections and chronic immune responses.
Monocytes
Cleanup crew that becomes macrophages in tissues. Elevated in chronic infections and autoimmune conditions.
Eosinophils
Specialised for allergic reactions and parasitic infections. Elevated in asthma, hay fever, and eczema.
Basophils
Rarest white cell. Releases histamine and heparin. Plays a role in allergic inflammation and hypersensitivity.
Platelets
Your repair crew
Platelet Count
Total number of platelets. Low counts (thrombocytopenia) increase bleeding risk; high counts (thrombocytosis) may increase clotting risk.
MPV (Mean Platelet Volume)
Average size of platelets. Larger platelets are younger and more active. High MPV with low count suggests increased platelet destruction.
Complete FBC Reference Ranges
Reference ranges vary slightly between laboratories. The values below are based on guidelines from the Royal College of Pathologists of Australasia (RCPA) and WHO. Always compare your results against the ranges printed on your specific pathology report.
Gender-specific ranges are shown where clinically relevant. Where ranges are identical for men and women, the same value appears in both columns.
| Marker | Full Name | Men | Women | Units | What It Tells You |
|---|---|---|---|---|---|
| Hb | Haemoglobin | 130-175 | 115-165 | g/L | Oxygen-carrying capacity of blood |
| RBC | Red Blood Cells | 4.5-6.5 | 3.8-5.8 | x10¹²/L | Total red cell production |
| Hct | Haematocrit | 0.40-0.54 | 0.36-0.48 | L/L | Percentage of blood that is red cells |
| MCV | Mean Cell Volume | 80-100 | 80-100 | fL | Average red cell size |
| MCH | Mean Cell Haemoglobin | 27-33 | 27-33 | pg | Average haemoglobin per cell |
| MCHC | Mean Cell Hb Conc. | 310-360 | 310-360 | g/L | Haemoglobin concentration in cells |
| RDW | Red Cell Distribution Width | 11.5-14.5 | 11.5-14.5 | % | Variation in red cell size |
| WBC | White Blood Cells | 4.0-11.0 | 4.0-11.0 | x10⁹/L | Total immune cell count |
| Neut | Neutrophils | 2.0-7.5 | 2.0-7.5 | x10⁹/L | Bacterial infection fighters |
| Lymph | Lymphocytes | 1.0-4.0 | 1.0-4.0 | x10⁹/L | Viral defence and antibody production |
| Mono | Monocytes | 0.2-0.8 | 0.2-0.8 | x10⁹/L | Chronic infection response |
| Eos | Eosinophils | 0.04-0.4 | 0.04-0.4 | x10⁹/L | Allergy and parasite response |
| Baso | Basophils | 0.0-0.1 | 0.0-0.1 | x10⁹/L | Histamine release and allergic response |
| Plt | Platelet Count | 150-400 | 150-400 | x10⁹/L | Blood clotting capacity |
| MPV | Mean Platelet Volume | 7.5-12.0 | 7.5-12.0 | fL | Average platelet size and activity |
Red Cell Indices Explained
The red cell indices (MCV, MCH, MCHC, RDW) are calculated values that describe the size, weight, and haemoglobin concentration of your red blood cells. Together, they classify anaemia into types that point toward specific causes. MCV is the most clinically useful of the four.
MCV: Red Cell Size Classification
Microcytic
MCV < 80 fL -- Iron deficiency, thalassaemia
Normocytic
MCV 80-100 fL -- Normal size, but anaemia still possible
Macrocytic
MCV > 100 fL -- B12/folate deficiency, liver disease
MCH (Mean Cell Haemoglobin)
Normal: 27-33 pg
Measures the average weight of haemoglobin in each red cell. MCH closely parallels MCV -- when cells are small (low MCV), they carry less haemoglobin (low MCH). Useful for confirming iron deficiency when MCV is borderline.
MCHC (Mean Cell Hb Concentration)
Normal: 310-360 g/L
Indicates how densely packed with haemoglobin each red cell is. Low MCHC (hypochromia) is seen in iron deficiency. Elevated MCHC is relatively rare but characteristic of hereditary spherocytosis, where cells are abnormally dense.
RDW (Red Cell Distribution Width)
Normal: 11.5-14.5%
Measures variation in red cell size (anisocytosis). A high RDW with a low MCV often indicates iron deficiency, while a normal RDW with a low MCV points toward thalassaemia trait. RDW is also elevated early in B12/folate deficiency and during treatment as new normal-sized cells mix with old abnormal ones.
White Cell Differential
The white cell differential breaks down your total WBC count into its five component types. Each type has a specialised role in your immune system. The proportions shift depending on whether you are fighting bacteria, viruses, parasites, or dealing with allergies.
Typical White Cell Proportions in Healthy Adults
Neutrophils
First cells to arrive at a bacterial infection site. They engulf and destroy bacteria through phagocytosis. A high neutrophil count (neutrophilia) is the hallmark of acute bacterial infection, while a low count (neutropenia) leaves you vulnerable to infections.
Lymphocytes
B-lymphocytes produce antibodies that tag pathogens for destruction. T-lymphocytes directly kill virus-infected cells and coordinate the immune response. Elevated lymphocytes (lymphocytosis) typically indicate viral infections such as glandular fever or chronic immune activation.
Monocytes
Circulate in blood for 1-3 days before migrating into tissues and becoming macrophages. They clean up dead cells, present antigens to lymphocytes, and produce cytokines. Elevated monocytes can indicate chronic infection, autoimmune disease, or recovery from acute infection.
Eosinophils
Release toxic granules that destroy parasites too large for phagocytosis. Also major players in allergic inflammation. Elevated eosinophils (eosinophilia) are seen in asthma, hay fever, eczema, drug allergies, and parasitic worm infections.
Basophils
The rarest white blood cell. Releases histamine and heparin to promote blood flow to injured tissues. Plays a role in immediate hypersensitivity reactions (anaphylaxis) and chronic allergic conditions. Rarely elevated in isolation.
Common FBC Patterns
Doctors diagnose blood disorders by recognising patterns across multiple markers, not by looking at a single number in isolation. The table below shows six common patterns and what they typically indicate.
| Pattern | Hb | WBC | Platelets | MCV | Likely Cause |
|---|---|---|---|---|---|
Iron Deficiency Anaemia | Low | Normal | Normal/High | Low | Insufficient iron for haemoglobin production. Most common anaemia worldwide. |
B12 / Folate Deficiency | Low | Low/Normal | Low | High | Impaired DNA synthesis causes large, immature red cells (megaloblastic anaemia). |
Bacterial Infection | Normal | High (Neutrophils) | Normal/High | Normal | Bone marrow releases stored neutrophils rapidly. Platelet rise is reactive. |
Viral Infection | Normal | Low/Normal (Lymph High) | Normal | Normal | Lymphocytes expand to produce antibodies. Total WBC may be normal or slightly low. |
Chronic Disease Anaemia | Low | Variable | Variable | Normal/Low | Inflammation traps iron in storage. Common in autoimmune disease and chronic kidney disease. |
Leukaemia Concern | Low/Normal | Very High or Very Low | Low | Variable | Abnormal white cell production crowds out normal cells. Requires urgent specialist review. |
When Your Doctor Orders an FBC
An FBC is one of the most versatile diagnostic tools in medicine. Here are six of the most common clinical reasons your doctor may request one.
Routine Health Checkup
Part of an annual physical examination. Provides a baseline for comparison and screens for common conditions before symptoms appear.
Fatigue Investigation
Unexplained tiredness is the most common reason for ordering an FBC. Low haemoglobin, low iron stores, or abnormal white cells can all cause persistent fatigue.
Pre-Surgery Assessment
Surgeons need to know your haemoglobin and platelet count before any procedure. Low Hb may require transfusion; low platelets increase surgical bleeding risk.
Monitoring Medications
Chemotherapy, immunosuppressants, anticonvulsants, and methotrexate can suppress bone marrow. Regular FBCs detect cytopenia early, before complications arise.
Suspected Infection
A high white cell count with neutrophil predominance suggests bacterial infection. Lymphocyte elevation points toward viral causes. The differential guides treatment decisions.
Unexplained Bruising or Bleeding
Easy bruising, prolonged bleeding from cuts, or petechiae (tiny red spots) can signal low platelet counts or platelet dysfunction. An FBC is the first-line investigation.
Important Notes About Your FBC
Tests Often Ordered Alongside an FBC
An FBC rarely tells the full story on its own. Your doctor may order additional tests to investigate abnormalities found on your FBC.
Iron Studies (Ferritin, Serum Iron, TIBC)
Investigate low Hb with low MCV (microcytic anaemia)
Vitamin B12 and Folate
Investigate low Hb with high MCV (macrocytic anaemia)
Reticulocyte Count
Measures new red cell production to distinguish production failure from destruction
Blood Film (Peripheral Smear)
Manual microscope examination of cell shape, size, and abnormalities
CRP / ESR (Inflammatory Markers)
Investigate elevated WBC to distinguish infection from inflammation
Coagulation Studies (PT, APTT)
Investigate bleeding tendency when platelets are normal
Track Your Blood Count Over Time
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