The Most-Ordered Blood Test in Australia
The Full Blood Count — written as FBC on Australian reports, sometimes CBC on imported ones — is the single most-ordered pathology test in the country, with over 30 million performed each year. It''s a screening tool, a diagnostic tool, and a monitoring tool all at once. Almost every patient who walks into a GP, ED, or specialist clinic gets one.
Despite its ubiquity, most patients receive a printout dense with abbreviations and numbers, and no real explanation of what to focus on. This guide breaks down each line, the patterns that matter, and the situations that need urgent review versus a calm repeat in 4 weeks.
What''s Actually in an FBC
The FBC measures three cell lines plus their derived indices:
| Line | Markers measured | What it tells you |
|---|---|---|
| Red cells | Haemoglobin (Hb), RBC, haematocrit (Hct), MCV, MCH, MCHC, RDW | Oxygen-carrying capacity. Anaemia and its likely cause. |
| White cells | WBC + 5-part differential: neutrophils, lymphocytes, monocytes, eosinophils, basophils | Immune system status. Infection, allergy, inflammation, leukaemia. |
| Platelets | Platelet count, MPV (mean platelet volume) | Clotting. Bleeding risk, recent infection, bone marrow status. |
Australian Reference Ranges
RCPA-aligned ranges used by Sullivan Nicolaides, Dorevitch, Laverty, Australian Clinical Labs, 4Cyte and most public lab networks:
| Marker | Reference range |
|---|---|
| Haemoglobin (men) | 130–180 g/L |
| Haemoglobin (women) | 115–160 g/L |
| RBC (men) | 4.5–6.5 ×10¹²/L |
| RBC (women) | 3.8–5.8 ×10¹²/L |
| MCV | 80–100 fL |
| MCH | 27–32 pg |
| RDW | 11.5–14.5% |
| Platelets | 150–400 ×10⁹/L |
| WBC (total) | 4.0–11.0 ×10⁹/L |
| Neutrophils | 2.0–7.5 ×10⁹/L |
| Lymphocytes | 1.0–4.0 ×10⁹/L |
| Monocytes | 0.2–1.0 ×10⁹/L |
| Eosinophils | 0.0–0.5 ×10⁹/L |
| Basophils | 0.0–0.2 ×10⁹/L |
Reading the Red Cell Story
If your haemoglobin is low (anaemia), the next number to look at is MCV. It splits anaemia into three buckets that almost always point at different causes:
Microcytic (MCV < 80 fL): "the cells are too small"
Almost always iron deficiency in Australia — the most common nutritional deficiency in the country, affecting 1 in 5 menstruating women. Confirm with ferritin (low) and iron studies. Other causes: thalassaemia trait (common in Australians of Mediterranean, Middle Eastern, South-East Asian, or African background), and rarely chronic lead exposure.
Normocytic (MCV 80–100 fL): "the cells are the right size, but there are not enough"
Suggests anaemia of chronic disease (kidney disease, chronic infection, autoimmune conditions like rheumatoid arthritis), recent blood loss (gastrointestinal bleeding, heavy periods within the last few weeks), or early iron deficiency before MCV has dropped. Reticulocyte count helps separate "not making cells" from "losing cells".
Macrocytic (MCV > 100 fL): "the cells are too big"
Most common Australian causes: B12 deficiency (especially in vegans, vegetarians, and people on metformin or PPIs long-term), folate deficiency, hypothyroidism, alcohol overuse, and certain medications (methotrexate, chemotherapy). Always check B12, folate, TSH, and LFTs before assuming a single cause.
Reading the White Cell Story
The total WBC alone tells you very little — the differential is what matters. Each of the five white cell lines has a typical reason for rising:
- Neutrophils high (>7.5): bacterial infection, recent surgery or trauma, steroid use, intense exercise within the last 24 hours.
- Neutrophils low (<2.0): viral infection, certain medications (some antibiotics, antithyroid drugs, chemotherapy), and ethnic neutropenia (common in Australians of African or Middle Eastern background — typically harmless and stable).
- Lymphocytes high (>4.0): viral infection (EBV, CMV, COVID-19, influenza), chronic infection (TB, hepatitis), and rarely chronic lymphocytic leukaemia (CLL) — usually flagged by a haematology review.
- Eosinophils high (>0.5): allergic conditions (asthma, eczema, drug reactions), parasitic infections (relevant after travel to endemic regions), and rarely haematological causes.
- Monocytes high: chronic infection (TB, endocarditis), inflammatory conditions, recovery from acute infection.
Reading the Platelet Story
Platelets sit between 150 and 400 ×10⁹/L in most healthy Australians. Mild deviations are usually benign:
- Platelets 100–149: common and often viral, medication-related (aspirin, anticonvulsants, certain antibiotics), or pregnancy-related. The most common Australian cause of an unexpectedly low result is actually a laboratory artefact — EDTA-induced platelet clumping. Your lab will usually rerun the test from a citrate tube to confirm.
- Platelets 50–99: warrants a repeat in 1–2 weeks and a review of medications and recent illness.
- Platelets <50: always urgent. Especially with bruising, bleeding, petechiae, or recent infection. Same-day GP or ED review.
- Platelets >450 (thrombocytosis): usually reactive — recent infection, inflammation, iron deficiency, or recent surgery. Sustained values >600 over multiple tests need haematology review for essential thrombocythaemia.
The Patterns That Matter
Looking at one line in isolation is often misleading. The patterns that should always trigger further workup:
- All three lines low (pancytopenia): bone marrow problem until proven otherwise. Urgent haematology review.
- Low Hb + low MCV + low ferritin: classic iron deficiency anaemia. Investigate the cause (heavy periods, gastrointestinal bleeding, dietary).
- Low Hb + high MCV + low B12 or folate: B12/folate deficiency. Replace and recheck in 8–12 weeks.
- High WBC + high neutrophils + high CRP: active bacterial infection. Find the source.
- Persistent eosinophilia + travel history: consider parasitic infection. Stool ova/cyst/parasite screening or referral.
- Persistent unexplained lymphocytosis > 5 × 10⁹/L over multiple FBCs: needs a haematology review for CLL.
What Affects FBC Accuracy
- Recent intense exercise — falsely raises WBC (especially neutrophils) for up to 24 hours.
- Pregnancy — Hb falls (haemodilution), WBC rises slightly. Both normalise after delivery.
- EDTA tube clumping — falsely lowers platelets in around 0.1% of samples. Labs will repeat from citrate tube.
- Sample age — a sample older than 6 hours can show artefactually low platelets and altered MCV.
- Recent steroid dose — raises WBC and neutrophils within hours.
Tracking FBCs Over Time
A single FBC is a snapshot. The most useful question is whether your numbers are drifting in one direction — slowly falling haemoglobin over years often points to chronic blood loss long before the absolute value is alarming. Most Australian pathology portals only show your last few results — uploading every PDF to BloodTrack reveals the long-range trend across red cells, white cells, and platelets together with your iron studies, B12, folate, TSH, and CRP — exactly the markers an FBC pattern points you to investigate.
Bottom Line
The FBC is more diagnostic than most patients realise — but only when read as a pattern, not a list of single numbers. Always look at MCV before assuming a cause for low haemoglobin, look at the differential before reacting to a high WBC, and don''t panic about mildly low platelets without a repeat test. For anything in the urgent ranges (severe anaemia, very low platelets, very high WBC, all-three-lines down), your GP will refer for same-day or next-day review.