At a Glance

Why It's Ordered
Anemia, bleeding, infection, or a suspected platelet or white cell problem: whether to transfuse, whether a febrile patient is neutropenic, and whether bleeding risk is safe for a procedure.
Check First
Hgb and Hct (oxygen-carrying capacity and bleeding), platelets (bleeding risk), WBC with ANC (infection and neutropenia). MCV classifies anemia but does not change acute management.
Critical Values
Hgb <7 or >20 g/dL · Platelets <30 or >1,000 ×10³/µL · WBC <2.0 or >30 ×10³/µL · ANC <0.5 ×10³/µL
Don't Miss
Hemoglobin lags acute hemorrhage, so a normal early value does not exclude major blood loss. Judge by vital signs, bleeding source and trend, and repeat the count.
Field & Transport
Most EMS systems have no on-scene CBC. Obtain the sending facility's latest Hgb, platelets and ANC with draw times. A CBC drawn before a bleed or transfusion may not reflect current status.

Panel Overview

The complete blood count (CBC) measures red cells, white cells and platelets in one draw. The panel has 10 measured components: RBC count, hemoglobin, hematocrit, MCV, MCH, MCHC, RDW, WBC count, the WBC differential and platelet count. It is ordered in ED, ICU and pre-transfer care to decide on transfusion, bleeding risk and infection risk.

The CBC is the hematology counterpart of the chemistry panels. It pairs with the coagulation panel when bleeding is the question. Hemoglobin and hematocrit describe oxygen-carrying capacity, platelets describe clotting capacity, and the absolute neutrophil count (ANC) describes infection risk.

When to Order:
  • Sepsis or fever: WBC with differential to assess infection and calculate the ANC.
  • Bleeding or trauma: hemoglobin and platelet trend after hemorrhage or GI bleeding.
  • Weakness, dyspnea, pallor or syncope: screen for anemia.
  • Chemotherapy or new cytopenia: ANC and platelet count before treatment decisions.
  • Heparin exposure: platelet trend when counts fall (heparin-induced thrombocytopenia).
  • Pre-procedure or pre-transfer: platelet count before lumbar puncture or a high-bleed-risk procedure.

Red Cells (Erythrocytes)

RBC Count

Normal: 3.9–5.5 ×10⁶/µL adults (women 3.8–5.2)

Red cells per microliter. Low in blood loss, hemolysis, marrow failure or nutritional deficiency; high in polycythemia or dehydration.

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Hemoglobin (Hgb)

Normal: M 14.0–17.5 | F 12.0–16.0 g/dL

Oxygen-carrying protein and the main number for transfusion decisions. Judge the trend and the patient, not one value.

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Hematocrit (Hct)

Normal: 41–50 % adults (women 35–47)

Percent of blood volume that is red cells, roughly three times the hemoglobin. Changes with hydration and lags acute bleeding.

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MCV

Normal: 80–100 fL

Mean red cell size. Under 80 fL is microcytic (iron deficiency, thalassemia trait); over 100 fL is macrocytic (B12 or folate deficiency, alcohol, liver disease).

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MCH

Normal: 27–33 pg

Mean hemoglobin per red cell. Tracks with MCV; low in microcytic anemias such as iron deficiency and thalassemia.

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MCHC

Normal: 32–36 g/dL

Hemoglobin concentration per red cell volume. Low in hypochromia; high in spherocytosis and some analyzer artifacts such as lipemia or cold agglutinins.

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RDW

Normal: 11.5–14.5 %

Variation in red cell size. High RDW with a normal MCV can be early iron deficiency or a mixed anemia.

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White Blood Cells (Leukocytes)

WBC Count

Normal: 4.5–11.0 ×10³/µL

Total leukocytes. High in infection, inflammation, stress, steroids or leukemia; low in marrow suppression, some viral infections and severe sepsis.

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WBC Differential

Normal: five cell types (see Reference table)

Share of neutrophils, bands, lymphocytes, monocytes, eosinophils and basophils. Bands (left shift) suggest acute bacterial infection; eosinophilia suggests allergy, drugs or parasites.

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Platelets (Thrombocytes)

Platelet Count

Normal: 150–400 ×10³/µL

Clotting cells. Bleeding risk rises as the count falls; transfusion thresholds depend on the clinical setting. Falls in heparin-induced thrombocytopenia, sepsis, DIC and marrow failure.

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Calculated Values

Absolute Neutrophil Count (ANC)

Normal: 1.5–8.0 ×10³/µL

WBC × (% neutrophils + % bands). Below 1.5 is neutropenia and below 0.5 is severe; with fever, it defines febrile neutropenia.

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Common Add-Ons

ESR

Normal: M 0–15 | F 0–20 mm/hr (under 50 y)

Nonspecific inflammation marker. Very high values prompt a search for infection, malignancy or giant cell arteritis.

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Reticulocyte Count

Normal: lab-specific interval

Young red cells; shows whether marrow is responding to anemia. High after bleeding or hemolysis, low in marrow failure.

Type and Screen

Expected: ABO and RhD typed, antibody screen negative

Blood bank test ordered alongside the CBC, not part of the count. ABO, RhD and an antibody screen decide which red cells can be given safely. When delay could be fatal, start uncrossmatched group O per protocol.

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Blood Cultures

Normal: no growth

Microbiology test ordered alongside the CBC, not part of the count. Two sets from separate sites identify the organism. Draw them before the first antibiotic dose only when that does not delay it.

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Reference Ranges & Critical Values
TestAdult Normal (conventional)SI UnitsCritical LowCritical HighNotes
RBC Count
3.9–5.5 adults (women 3.8–5.2) ×10⁶/µL
3.9–5.5 adults (women 3.8–5.2) ×10¹²/L
—
—
Adult range (Critical Care Transport, sex not stated); women's value from Rosen's Table 121-1; lab-dependent
Hemoglobin (Hgb)
M 14.0–17.5 | F 12.0–16.0 g/dL
M 140–175 | F 120–160 g/L
<7 g/dL
>20 g/dL
Sex-specific; lab-dependent
Hematocrit (Hct)
41–50 % adults (women 35–47)
0.41–0.50 adults (women 0.35–0.47) L/L
—
—
Adult range (Critical Care Transport, sex not stated); women's value from Rosen's Table 121-1; lab-dependent
MCV
80–100 fL
80–100 fL
—
—
Lab-dependent
MCH
27–33 pg
27–33 pg
—
—
Lab-dependent
MCHC
32–36 g/dL
320–360 g/L
—
—
Lab-dependent
RDW
11.5–14.5 %
Same (%)
—
—
Lab-dependent
WBC Count
4.5–11.0 ×10³/µL
4.5–11.0 ×10⁹/L
<2.0 ×10³/µL
>30 ×10³/µL
Lab-dependent
WBC Differential
Five cell types (% of WBC)
Same (%)
—
—
Cell-specific ranges
ANC (calculated)
1.5–8.0 ×10³/µL
1.5–8.0 ×10⁹/L
<0.5 ×10³/µL
—
Calculated from WBC and differential
Platelet Count
150–400 ×10³/µL
150–400 ×10⁹/L
<30 ×10³/µL (lab-specific; many labs call at 20)
>1,000 ×10³/µL
Recheck if clumped
ESR
M 0–15 | F 0–20 mm/hr (under 50 y)
Same (mm/hr)
—
—
Age, sex and method dependent
Reticulocyte Count
Lab-specific interval
Lab-specific
—
—
Percent and absolute counts vary
Reference intervals: Every lab sets its own intervals and critical lists, and the analyzer and assay shift them too. Use the interval your lab reports and follow its critical-call policy.

Children get their own ranges under Special Populations. The transfusion thresholds sit under Critical Findings.

Systematic Interpretation
  1. Hemoglobin and hematocrit: confirm anemia against the sex-specific lower limit and check the trend. Hematocrit should be about three times the hemoglobin.
  2. MCV: classify as microcytic (<80 fL), normocytic or macrocytic (>100 fL). Reticulocyte count separates marrow failure from blood loss or hemolysis.
  3. RDW: a high RDW with a normal MCV suggests early iron deficiency or mixed deficiencies.
  4. WBC and ANC: calculate the ANC. Below 1.5 ×10³/µL is neutropenia; below 0.5 ×10³/µL is severe. Check bands and atypical cells on the differential.
  5. Platelets: below 150 ×10³/µL is thrombocytopenia. An unexpected low count may be EDTA clumping; recheck before treating (see Specimen Collection).
  6. Context: check bleeding, heparin or chemotherapy exposure, and recent transfusion before labeling a result.
Hematocrit rule of thumb
Hct (%) ≈ 3 × Hgb (g/dL)

A Hct far from three times the Hgb points to sampling or analyzer error. It can also mean unusually sized red cells.

Absolute neutrophil count
ANC (×10³/µL) = WBC (×10³/µL) × (% neutrophils + % bands) ÷ 100

Normal sits near 1.5–8.0 ×10³/µL. Under 1.5 is neutropenia. Under 0.5 is severe neutropenia.

Worked Example: Say the WBC is 2.4 ×10³/µL with 40% neutrophils and 5% bands. ANC = 2.4 × 45 ÷ 100 = 1.08 ×10³/µL, which is neutropenia. A total that looks normal can hide this. Calculate the ANC.

Patterns & Differential

Read the red cell indices first, then the ANC and the platelet count. Two or three of these values identify most cytopenia patterns.

PatternKey FindingsCommon CausesNext Step
Microcytic anemia
Low Hgb, MCV <80 fL, low MCH and MCHC
Iron deficiency, thalassemia trait, chronic inflammation
Ferritin and iron studies; hemoglobin electrophoresis if thalassemia is suspected
Macrocytic anemia
MCV >100 fL
B12 or folate deficiency, alcohol, liver disease, marrow disorders, high reticulocytes
B12, folate, reticulocyte count and smear
Normocytic anemia, low reticulocytes
Normal MCV, reticulocyte count low
Anemia of chronic disease or kidney disease, early iron deficiency, marrow suppression
Renal function, inflammatory markers and smear
Normocytic anemia, high reticulocytes
Low Hgb with a rising reticulocyte count
Hemorrhage, hemolysis
Locate the bleeding source; hemolysis markers and smear
Pancytopenia
Low RBC, WBC and platelets together
Marrow failure, leukemia, drug toxicity, severe sepsis
Smear and urgent hematology referral
Neutropenia with fever
ANC <0.5 ×10³/µL and fever
Chemotherapy, marrow suppression, overwhelming infection
Urgent empiric antibiotics per protocol; see Critical Findings
Platelet fall after heparin
Platelet fall during heparin exposure, often 5–10 days after start; new thrombosis possible
Heparin-induced thrombocytopenia (immune)
Estimate probability with the 4Ts score; stop heparin when intermediate or high
Thrombocytopenia with schistocytes
Low platelets, anemia, fragmented red cells on smear
TTP, HUS, DIC, HELLP
Urgent hematology or ICU care; check LDH, creatinine and coagulation

Serial Testing & Kinetics
AnalyteChange Over TimeRepeatMonitoring Target
Hemoglobin and hematocrit
Falls with ongoing bleeding and with fluid dilution; a normal early value does not exclude hemorrhage
With clinical change or per protocol
Trend against bleeding control and symptoms
Platelet count
In heparin-induced thrombocytopenia the fall typically appears 5–10 days after heparin starts
Per protocol during heparin exposure
A fall prompts a 4Ts assessment and stopping heparin
ANC
Nadir timing depends on the chemotherapy regimen
Per oncology protocol
Recovery to ANC 0.5 ×10³/µL or higher

Critical Findings & Emergency Actions

Hemorrhage with hemodynamic change (Paramedic/RN/CCT)

Recognize: Active bleeding, tachycardia, falling blood pressure or altered mental status. Hemoglobin may still be normal early.

  1. Control external bleeding and maintain airway and oxygenation per protocol.
  2. Establish two large-bore IV or IO access per protocol (Paramedic/RN).
  3. Treat shock per protocol; limit crystalloid to what perfusion requires, because large volumes dilute red cells and clotting factors.
  4. Notify the receiving team early so blood products can be prepared, per receiving-facility protocol.
Pitfall: Hemoglobin falls only as fluids equilibrate. A normal early value after hemorrhage is not reassurance.

Symptomatic anemia with hemoglobin below 7 g/dL (RN/CCT)

Recognize: Hemoglobin below 7 g/dL with chest pain, dyspnea, syncope or ECG evidence of ischemia.

  1. Give supplemental oxygen per protocol and assess for ongoing bleeding.
  2. Obtain a 12-lead ECG and monitor for ischemia.
  3. Transfusion is a receiving-team decision. AABB 2023 restrictive default is below 7 g/dL in hemodynamically stable hospitalized adults; 7.5 g/dL is an option for cardiac surgery and 8 g/dL for orthopedic surgery or preexisting cardiovascular disease. These thresholds do not apply to unstable hemorrhage. With active ischemia or acute MI, the target is individualized by the treating team.
  4. Report the hemoglobin value and draw time at handoff. Transfusion from the field follows local policy and medical direction.

Platelets below 20 ×10³/µL with bleeding or a planned procedure (RN/CCT)

Recognize: Petechiae, mucosal bleeding or a planned lumbar puncture with platelets below 20 ×10³/µL.

  1. Hold non-essential intramuscular injections and avoid antiplatelet agents and NSAIDs unless the prescriber directs.
  2. Notify the team before lumbar puncture or line placement. AABB 2025 transfusion thresholds: below 20 ×10³/µL for lumbar puncture; below 10 ×10³/µL for central venous catheter placement in compressible sites (conditional). These are for nonbleeding patients and procedures. Thresholds for active significant bleeding, major surgery or neurosurgery are higher and set by the treating team per local protocol.
  3. Apply direct pressure to bleeding sites and report the bleeding rate.
  4. Platelet transfusion is a receiving-team decision per protocol.

Febrile neutropenia (ANC below 0.5 ×10³/µL with fever) (RN/CCT)

Recognize: Single oral temperature of 38.3 °C (101 °F) or higher, or 38.0 °C (100.4 °F) sustained over 1 hour, with ANC below 0.5 ×10³/µL or expected to fall below it within 48 hours as defined by the IDSA 2010 guideline.

  1. Treat as an emergency and screen for sepsis; start the sepsis protocol if criteria are met.
  2. Draw blood cultures before antibiotics if this does not delay them.
  3. Empiric antibiotics should be given urgently; IDSA 2010 advises starting within 2 hours of presentation, and many institutional pathways target sooner. Follow receiving-facility protocol.
  4. Avoid rectal temperatures, rectal medications and intramuscular injections. Notify the receiving team of the ANC and draw time.
Pitfall: A normal total WBC does not exclude neutropenia. Use the ANC.

Suspected heparin-induced thrombocytopenia (RN/CCT)

Recognize: Platelet fall during heparin exposure (commonly 5–10 days after start), or new thrombosis while on heparin.

  1. High-alert Stop all heparin, including flushes and low-molecular-weight heparin such as enoxaparin, when the 4Ts probability is intermediate or high per the ASH 2018 guideline.
  2. A low 4Ts score makes HIT unlikely; ASH 2018 recommends against empiric treatment (stopping heparin and starting a non-heparin anticoagulant) in that group.
  3. Notify the team. Avoid routine platelet transfusion; active bleeding is the exception the treating team weighs. Do not start warfarin before platelet recovery (ASH 2018, strong recommendation). A non-heparin anticoagulant is chosen and started by the treating team.
  4. Use heparin-free flush and line-care protocols during transport.
Pitfall: EDTA clumping can falsely lower the platelet count. Repeat in a citrate tube or on a smear before treating a low count.

Prehospital & Transport Considerations

Point-of-Care Testing

Device or MethodAnalytesSpecimenLimitations
Handheld hemoglobin or hematocrit meter
Hgb or Hct (estimate)
Capillary or venous
Shifts with hydration and perfusion; not a substitute for the laboratory CBC
Laboratory CBC at receiving facility
All components, ANC
Lavender (EDTA)
Requires the laboratory; no standard field equivalent for platelets or ANC

Interfacility Transfer & Handoff

  • Results to obtain: latest Hgb, Hct, platelet count and ANC, with draw times, and any transfusion given (product and time).
  • Medications: heparin, low-molecular-weight heparin, antiplatelet agents and recent chemotherapy. Each one changes how you read the result.
  • Repeat en route: only if the sending team's CBC is outdated and bleeding is ongoing, or per receiving-facility protocol.
  • Specimen handling: get EDTA samples there fast. Room temperature is preferred. Delay alters WBC and platelet results. Follow laboratory policy on storage.

Scope Notes

  • Most systems make transfusion a hospital-level decision. EMS and CCT follow local protocol and medical direction.
  • Platelet and ANC results can move procedure timing and drug choice. Confirm them with the receiving team.

Special Populations

Pediatrics

Pediatric intervals shift with age. Neonatal hemoglobin and WBC are higher than adult values, and platelet ranges follow age-specific limits. Use the age-specific interval from the reporting laboratory. The age-band tables are not on this page.

AABB 2025 recommends platelet transfusion for neonates with consumptive thrombocytopenia and no major bleeding when the count is below 25 ×10³/µL (strong recommendation). Need vital-sign norms by age? See pediatric vital signs. Blood product volumes are weight-based per local protocol. The dosing math is at weight-based dosing.

Pregnancy

  • Dilutional anemia: plasma expands, so hemoglobin falls. Hematocrit falls with it. Anemia threshold: Hgb below 11 g/dL in the first and third trimesters, below 10.5 g/dL in the second.
  • Platelets: gestational thrombocytopenia is common and usually mild. Evaluate a low or falling count. Do not blame pregnancy alone. A falling count with hypertension, elevated liver enzymes or hemolysis points to HELLP or preeclampsia.

Older Adults

Anemia is not part of normal aging. It needs a workup, not reassurance.

CKD and Dialysis

CKD anemia is usually normocytic, with a low reticulocyte count. Iron status and erythropoiesis-stimulating therapy move the hemoglobin target. Transfusion in chronic anemia is the treating nephrology or medical team's call.

Specimen Collection & Interfering Factors
  • Specimen and tube: lavender (K₂EDTA) for the CBC. ESR runs from a lavender EDTA tube (modified Westergren) or a black-top 3.8% sodium citrate tube. The laboratory decides which. Tube colours vary by institution.
  • Fill and mix: fill to the marked line and mix gently. An underfilled EDTA tube skews cell counts.
  • Handling: get it there promptly at room temperature. Delay shifts the white count and platelet results.
  • Order of draw (CLSI GP41): blood cultures, light blue, red or gold, green, lavender, gray.
Error or InterferentEffect on ResultsPrevention
EDTA clumping
Falsely low platelet count (pseudothrombocytopenia)
Recheck in a citrate tube or review the smear
Drawing above an IV line
Dilution: falsely low Hgb, Hct and platelets
Draw from the opposite arm or stop infusions and discard per protocol
Prolonged tourniquet
Hemoconcentration: falsely high Hgb and Hct
Limit tourniquet time
Delayed processing
Changed WBC and platelet counts
Deliver promptly; room temperature is preferred; follow laboratory policy
Cold agglutinins
Falsely high MCV, low RBC count
Warm the sample per laboratory policy; smear review
Lipemia
Falsely high MCHC and hemoglobin
Repeat on a non-lipemic sample

Clinical Pearls
Transfusion: AABB 2023 sets the default at below 7 g/dL for hospitalized, hemodynamically stable adults. The number is a starting point. Symptoms, ischemia and bleeding decide more.
Platelet thresholds: Thresholds depend on the setting. AABB 2025 gives below 10 ×10³/µL for nonbleeding chemotherapy patients and below 20 ×10³/µL before lumbar puncture.
ANC: The ANC tells you about infection risk. Work it out from the WBC and differential. Do not read the total WBC by itself.
Transport: Ask the sending facility when it was drawn. A CBC drawn before a bleed or transfusion may not show where the patient is now.
Nursing: Before IM injections, rectal medications or lines, check the platelet count and ANC when a recent result is available.
ICU: A falling platelet count during heparin therapy is a HIT trigger until proven otherwise. Read the 4Ts score and the timing together.
Pitfall: Hemoglobin lags behind acute bleeding. Judge the hemorrhage by vital signs, the bleeding source and the trend.

Related

References
  1. Carson JL, Stanworth SJ, Guyatt G, et al. Red Blood Cell Transfusion: 2023 AABB International Guidelines. JAMA. 2023. https://doi.org/10.1001/jama.2023.12914
  2. Metcalf RA, Nahirniak S, Guyatt G, et al. Platelet Transfusion: 2025 AABB and ICTMG International Clinical Practice Guidelines. JAMA. 2025;334(7):606–617. https://doi.org/10.1001/jama.2025.7529
  3. Cuker A, Arepally GM, Chong BH, et al. American Society of Hematology 2018 guidelines for management of venous thromboembolism: heparin-induced thrombocytopenia. Blood Adv. 2018;2(22):3360–3392. https://doi.org/10.1182/bloodadvances.2018024489
  4. Freifeld AG, Bow EJ, Sepkowitz KA, et al. Clinical Practice Guideline for the Use of Antimicrobial Agents in Neutropenic Patients with Cancer: 2010 Update by the Infectious Diseases Society of America. Clin Infect Dis. 2011;52(4):e56–e93. https://doi.org/10.1093/cid/cir073
  5. Evans L, Rhodes A, Alhazzani W, et al. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Crit Care Med. 2021;49(11):e1063–e1143. https://doi.org/10.1097/CCM.0000000000005337

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  • For Educational Purposes Only: This content is intended for educational reference and should not be used for clinical decision-making.
  • Not a Substitute for Professional Judgment: Always consult your local protocols, institutional guidelines, and supervising physicians.
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