Full Blood Count (FBC/CBC) Results Explained, Line by Line
A full blood count (FBC in the UK, complete blood count or CBC in the US) counts and measures your red cells, white cells and platelets. One NHS lab’s adult hemoglobin range is 130–180 g/L for men and 115–165 g/L for women; Mayo Clinic’s US range is 13.2–16.6 and 11.6–15.0 g/dL. One line slightly out of range is common in healthy people; the pattern matters more. A few results, such as neutrophils below 0.5 x109/L, need same-day action.
Units: hemoglobin g/L ÷ 10 = g/dL. Hematocrit 0.42 L/L = 42%. Counts in x109/L and x103/µL are the same number.
- Every line
- UK vs US units
- One flag
- Small cells
- Large cells
- High hemoglobin
- High white cells
- Low neutrophils
- Platelets
- Same-day results
What a full blood count includes, line by line
An FBC is one tube of blood run through an analyzer. In the US, a “CBC with differential” also splits the white cells into five types.
| Line (UK / US name) | What it shows | Example UK adult range | Example US adult range |
|---|---|---|---|
| Haemoglobin / Hemoglobin (Hb, HGB) | Oxygen-carrying protein | Men 130–180, women 115–165 g/L | Men 13.2–16.6, women 11.6–15.0 g/dL |
| Red cell count (RBC) | Number of red cells | Men 4.50–6.50, women 3.80–5.80 x1012/L | Men 4.35–5.65, women 3.92–5.13 x1012/L |
| Haematocrit / Hematocrit (Hct, PCV) | Share of blood that is red cells | Men 0.40–0.54, women 0.37–0.47 L/L | Men 38.3–48.6%, women 35.5–44.9% |
| MCV | Average red cell size | 80–100 fL | 78.2–97.9 fL |
| MCH | Hemoglobin per red cell | 27–32 pg | Men 27–33, women 26–33 pg* |
| MCHC | Hemoglobin concentration in red cells | 320–370 g/L* | 32–36 g/dL* |
| RDW | Variation in red cell size | 11.5–15.7%* | Men 11.8–14.5%, women 12.2–16.1% |
| White cell count (WCC, WBC) | All white cells | 3.6–11.0 x109/L | 3.4–9.6 x109/L |
| Neutrophils | Bacterial infection defense | 1.8–7.5 x109/L | 1.56–6.45 x109/L |
| Lymphocytes | Viral defense, immune memory | 1.0–4.0 x109/L | 0.95–3.07 x109/L |
| Monocytes | Clean-up cells | 0.2–0.8 x109/L | 0.26–0.81 x109/L |
| Eosinophils | Allergy and parasites | 0.1–0.4 x109/L | 0.03–0.48 x109/L |
| Basophils | Small allergy-related group | 0.02–0.10 x109/L | 0.01–0.08 x109/L |
| Platelets (PLT) | Start a clot | 140–400 x109/L | Men 135–317, women 157–371 x109/L |
UK: Gloucestershire Hospitals NHS, July 2026; *MCHC and RDW from Liverpool University Hospitals. US: Mayo Clinic Laboratories; *MCH and MCHC from MedlinePlus. Your report’s own range comes first.
The indices (MCV, MCH, MCHC, RDW) describe the cells themselves and help sort out the cause of a low hemoglobin (haemoglobin). See also white blood cell count and platelet count.
FBC vs CBC: names and units
The cells are the same; the units differ. Liverpool’s NHS lab moved its FBC to the national harmonised units in April 2013, so older UK results may look different.
| Line | UK report | US report | Convert |
|---|---|---|---|
| Hemoglobin | 135 g/L | 13.5 g/dL | g/L ÷ 10 |
| Hematocrit | 0.42 L/L | 42% | L/L x 100 |
| MCHC | 340 g/L | 34 g/dL | g/L ÷ 10 |
| White cells | 6.2 x109/L | 6.2 x103/µL or 6,200/µL | Same number |
| Platelets | 250 x109/L | 250 x103/µL or 250,000/µL | Same number |
| Red cell count | 4.8 x1012/L | 4.8 x106/µL | Same number |
| MCV, MCH, RDW | fL, pg, % | fL, pg, % | No change |
MedlinePlus writes 4,500–11,000 white cells per µL as 4.5–11.0 x109/L. Our blood test unit converter handles hemoglobin. Some UK reports label hematocrit PCV, for packed cell volume (North Bristol NHS Trust).
Why one slightly abnormal line is common
Each range holds the middle 95% of healthy people, so on every line 2.5% of healthy people sit below and 2.5% above. Oxford’s Bennett Institute worked through an FBC of 16 tests, each with a 5% chance of a flag. That gives a 56% chance of at least one abnormal flag. Labs also set their own ranges.
Sources: Gloucestershire Hospitals 2026; Liverpool University Hospitals; HSL Royal Free 2026; Mayo Clinic Laboratories; WHO 2024.
A hemoglobin of 118 g/L is inside the range at three of these labs, flagged low at the fourth, and anemia by the WHO cut-off. So treat a lone flag as a clue. MedlinePlus notes that an abnormal level doesn’t always mean a condition that needs treatment. Doctors weigh how far out it is, whether related lines move with it, your past results and your symptoms.
What a full blood count actually tells you
Your bone marrow makes all three cell types. Red cells carry oxygen, white cells fight infection and platelets plug leaks. Think of each line as a witness. One can be mistaken; three that tell the same story are hard to ignore.
Red cell size is the first clue in anemia (anaemia, UK spelling). Merck calls cells with an MCV below 80 fL small (microcytic) and above 100 fL large (macrocytic). A high RDW can be the only sign of a mix of small and large cells, which can leave the MCV looking normal.
Patterns worth acting on
Each card follows the clues to a next lead, using NHS haematology guidance for GPs.
Low hemoglobin with small cells
- Hemoglobin below range
- MCV below 80 fL, MCH low
- Iron deficiency
- Thalassemia trait (inherited)
- Long-term inflammation, sometimes (Merck)
Ferritin or full iron studies, then the reason for iron loss.
Manchester 2026: ferritin below 30 µg/L is low, and microcytic anemia needs a stool FIT test. MCV and MCH that stay low and unchanged suggest thalassemia trait.
Ask: Is my ferritin low? Where might I be losing iron? Could this be thalassemia trait?
High MCV (large red cells)
- MCV above 100 fL
- Hemoglobin normal or low
- Low B12 or folate
- Alcohol, liver disease, underactive thyroid
- Medicines such as methotrexate or hydroxycarbamide
- Pregnancy (a normal rise)
A repeat FBC, then B12, folate, liver and thyroid tests.
Manchester 2026: repeat first, as an old sample can raise the MCV. Referral is considered with no cause and an MCV above 105 fL plus other low counts, or above 110 fL.
Ask: Have my B12, folate and thyroid been checked? Could a medicine explain it?
Low hemoglobin with normal-sized cells
- Hemoglobin below range
- MCV within range
- Recent bleeding, before iron runs low (Merck)
- Kidney disease, inflammation, thyroid
- Mixed deficiencies (high RDW)
Reticulocytes, ferritin, B12, folate, kidney function (a U&E) and CRP.
RCPath asks labs to phone a normal-sized hemoglobin below 70 g/L, as it may mean blood loss or marrow failure.
Ask: Is my kidney function normal? Could I be losing blood?
High hemoglobin or hematocrit
- Hemoglobin and hematocrit above range
- Dehydration (MedlinePlus)
- Smoking or low oxygen from lung disease
- Testosterone, diuretics or SGLT2 inhibitors
- Altitude (WHO 2024)
A repeat when well hydrated, and a review of medicines and smoking.
Manchester 2026 flags hematocrit above 0.52 (52%) in men or 0.48 (48%) in women, repeats it in 2 months, and refers if it persists with no clear cause.
Ask: Could dehydration or a medicine explain this? When should we repeat it?
High white cell count
- Neutrophils above 8.5, lymphocytes above 5 or eosinophils above 0.5 x109/L
- Neutrophils: infection, inflammation, steroids, pregnancy, smoking
- Lymphocytes: viral infection or smoking; if persistent, CLL
- Eosinophils: allergy, parasites, medicines
A repeat once any infection settles.
Manchester 2026: lymphocytes 5–20 are repeated in 6 weeks; above 20 is an urgent suspected-cancer referral. Eosinophils above 5.0 are referred urgently.
Ask: Which white cell is high? Could an infection or medicine explain it?
Low neutrophils (neutropenia)
- Mild 1.0–1.5, moderate 0.5–1.0, severe below 0.5 x109/L
- A recent viral illness
- Medicines such as carbimazole, clozapine or methotrexate
- Autoimmune disease
- Duffy-null neutrophil count (see ancestry)
A repeat with a blood film, and your past results.
Norfolk and Norwich: if well, repeat in 7–10 days for below 1.0, or 4–6 weeks for 1.0–1.5. Below 0.5 with fever is a medical emergency.
Ask: Has my count always been low? What should I do if I get a fever?
Platelets low or high
- Low: below 100 x109/L
- High: above 450 x109/L
- Low: clumping in the tube (a false low), immune thrombocytopenia (ITP), alcohol, liver disease, medicines, low B12 or folate
- High: iron deficiency, infection, inflammation, recent surgery
Low: a blood film, and a repeat in a citrate (blue top) tube if clumps are seen. High: a repeat in 6 weeks with ferritin and CRP.
Manchester 2026: urgent referral for below 20 with bleeding, or above 1,000. Persistent unexplained counts above 450 are referred routinely.
Ask: Could this be clumping? When should we recheck?
What can throw off a full blood count
- Dehydration concentrates the blood (MedlinePlus lists it as a cause of abnormal hemoglobin).
- An old sample raises the MCV, and blood taken near a drip or partly clotted gives wrong results (University Hospitals Sussex). Labcorp accepts a CBC for 1 day at room temperature, 3 days chilled.
- Platelet clumping in the EDTA tube gives a false low count (Manchester 2026).
- Recent infection can lower or raise white cells for a while.
- Smoking and altitude raise hemoglobin; WHO 2024 adjusts anemia cut-offs for both.
- Medicines such as steroids, testosterone, methotrexate and carbimazole.
Pregnancy, ancestry and children
Pregnancy. UK haematology guidance used by NHS maternity units defines anemia as hemoglobin below 110 g/L in the first trimester, below 105 g/L in the second and third, and below 100 g/L after birth. WHO 2024 uses 110 g/L in the third trimester. Pregnancy can also raise neutrophils and the MCV (Manchester 2026).
Ancestry. Mild neutropenia without symptoms is common in people of sub-Saharan African, Arab or West Indian ancestry, and is strongly linked to the Duffy-null red cell type (CMAJ 2022). Norfolk and Norwich notes these counts usually stay above 1.0 and need no monitoring.
Children have their own ranges; the adult numbers here don’t apply.
Reading an FBC on your lab report or the NHS App
- Names: FBC in the UK; CBC or “CBC with differential” in the US. Look for Hb or HGB, WCC or WBC, and PLT.
- Missing lines: some UK labs don’t routinely report red cell count, MCH, MCHC or RDW (Liverpool University Hospitals).
- Percent vs absolute: guidance thresholds use the absolute white cell counts, not the percentages.
- Flags: results outside the lab’s range are usually marked H or L. Read the range printed beside yours.
- NHS App: you may see results your GP has not yet discussed with you (NHS). In a US portal, read each result against the range printed beside it. Contact your doctor if a result worries you.
Which FBC results need same-day action
RCPath’s 2026 guidance lists FBC results that UK labs should phone through quickly. Local limits differ, and US labs set their own critical values.
| Result | UK units | US units |
|---|---|---|
| Hemoglobin, small or large cells | Below 50 g/L | Below 5.0 g/dL |
| Hemoglobin, normal-sized cells | Below 70 g/L | Below 7.0 g/dL |
| Hemoglobin, high (urgent if other problems) | Above 190 g/L | Above 19.0 g/dL |
| Neutrophils | Below 0.5 or above 50 x109/L | Below 500 or above 50,000/µL |
| Lymphocytes | Above 50 x109/L | Above 50,000/µL |
| Platelets, low | Below 30 x109/L | Below 30,000/µL |
| Platelets, high | Above 600; urgent above 1,000 x109/L | Above 600,000; urgent above 1,000,000/µL |
| Blood film | Blasts, malaria parasites or many broken red cells | |
Manchester’s GP guide calls pancytopenia (all three cell lines low) severe if hemoglobin is below 80 g/L, neutrophils below 0.5 or platelets below 30 x109/L.
When to get help urgently
- You’re on chemotherapy or have very low neutrophils, and you get a high temperature or feel hot, cold, sweaty or shivery: call your care team now (NHS), or NHS 111 if you’re unsure how to reach them. In the US, get same-day care. Severe neutropenia with fever needs antibiotics straight away (CMAJ 2022).
- Low platelets and bleeding that won’t stop, or new confusion: call 999 (UK) or 911 (US).
- Low hemoglobin and chest pain, fainting or breathlessness at rest: call 999 or 911.
- You’ve been told to go to hospital because of a result: go now.
FBC questions people ask
Is an FBC the same as a CBC?
Yes. FBC is the UK name and CBC the US name. Hemoglobin is in g/L (UK) or g/dL (US), and hematocrit is a fraction (UK) or a percent (US).
Do I need to fast for a full blood count?
Usually not (MedlinePlus). You may need to if other tests, such as glucose, use the same blood draw.
Why is one of my FBC results slightly out of range?
Ranges cover 95% of healthy people, so with 16 lines there’s about a 56% chance of at least one flag (Bennett Institute). GP guidance often starts with a repeat.
What does a low MCV mean?
Small red cells. Iron deficiency and thalassemia trait are the usual suspects, so ferritin is the usual next test.
How do I convert hemoglobin from g/L to g/dL?
Divide by 10. A UK result of 125 g/L is 12.5 g/dL.
Can a full blood count detect cancer?
It can’t rule cancer in or out. Some blood cancers change it, such as very high lymphocytes or blasts on the film, and UK guidance refers these urgently.
How we wrote this page
Written and medically reviewed by Dr. Mustafa Sakr, MBBCh. Last reviewed: October 2026. The numbers come from UK guidance (RCPath, NHS haematology pathways, British pregnancy guidance), WHO 2024 and published UK and US lab ranges, listed below. We update this page when guidance changes.
How we chose the numbers: UK haematology ranges aren’t set nationally, so we show one NHS lab (Gloucestershire, July 2026) and name others where they differ. US ranges are Mayo Clinic Laboratories examples. There’s no checker, because an FBC is read as a pattern, with your history.
References
- Royal College of Pathologists. The communication of critical and unexpected pathology results (G158 v2), 2026. rcpath.org (PDF)
- Manchester University NHS FT. Haematology GP Pathway Guides v4, 2026. mft.nhs.uk (PDF)
- Norfolk and Norwich University Hospitals. Neutropenia in Adult Patients (H.A011 v9). nnuh.nhs.uk
- WHO. Guideline on haemoglobin cutoffs to define anaemia, 2024. who.int; summary
- Frimley Health and Care. Iron deficiency anaemia in pregnancy, 2020 (citing British Society for Haematology guidance). frimley.icb.nhs.uk (PDF)
- Gloucestershire Hospitals NHS FT. Haematology reference ranges, 2026. gloshospitals.nhs.uk
- NHS lab directories: Liverpool; University Hospitals Sussex; North Bristol; HSL Royal Free.
- Mayo Clinic Laboratories. CBC with Differential, Blood (9109). mayocliniclabs.com
- Labcorp. CBC With Differential (005009). labcorp.com
- MedlinePlus: CBC, 2024; RDW, 2024; RBC indices, 2026; WBC count, 2025; platelet count, 2025.
- Merck Manual Professional. Evaluation of Anemia, 2024. merckmanuals.com
- Mithoowani S, et al. Neutropenia. CMAJ 2022;194(49):E1689. cmaj.ca
- Bacon S. OpenPathology: Issues with reference ranges, Part 2. Bennett Institute, University of Oxford, 2019. bennett.ox.ac.uk
- NHS: Chemotherapy side effects, 2025; NHS App test results, 2026.
This page is for education only and isn’t medical advice, a diagnosis or a substitute for your own doctor, who knows your history. Reference ranges vary between laboratories. Always interpret results with a qualified clinician. See our medical disclaimer.
