Chart — Lab
CBC Interpretation Chart
WBC differential with causes, anemia classification by MCV type, platelet disorder thresholds, critical values, and nursing actions for complete blood count interpretation and NCLEX.
Educational use only. Reference ranges vary by laboratory and patient population. Interpret CBC in the context of patient history, medications, and clinical presentation. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
WBC Changes & Differential Interpretation
| Finding | Common Causes | Nursing Priority |
|---|---|---|
| Total WBC ↑ (Leukocytosis > 11,000) | Bacterial infection (most common), inflammation, steroid use, leukemia, stress response, necrosis, pregnancy | Assess for infection source; fever, localizing signs; culture before antibiotics; review recent steroids |
| Total WBC ↓ (Leukopenia < 4,500) | Viral infections, chemotherapy, aplastic anemia, bone marrow suppression, autoimmune disease, sepsis (later) | Neutropenic precautions if ANC < 1,000; report fever ≥ 38°C immediately; avoid fresh flowers, crowds, raw foods |
| Neutrophils ↑ (> 70%) | Bacterial infection, steroid use, physical stress, acute MI, inflammation, burns | Left shift (bands > 5%) = more urgent — indicates severe infection with release of immature cells |
| Neutrophils ↓ (< 55%) / ANC < 1,500 | Chemotherapy, viral infection, aplastic anemia, B12/folate deficiency, HIV | Calculate ANC = WBC × % neutrophils. ANC < 500 = severe neutropenia — implement reverse isolation |
| Lymphocytes ↑ (> 40%) | Viral infections (EBV, CMV, COVID), lymphoma, CLL, TB recovery | Atypical lymphocytes on differential = consider EBV (mono) or CLL workup |
| Monocytes ↑ (> 8%) | Chronic infections (TB, fungal), autoimmune disease, monocytic leukemia, inflammatory bowel disease | Persistent monocytosis warrants investigation for chronic inflammatory or infectious process |
| Eosinophils ↑ (> 4%) | Allergic reactions, asthma, parasitic infections, drug hypersensitivity, Addison's disease, Hodgkin's lymphoma | Correlate with respiratory symptoms (asthma) or travel history (parasites) |
Anemia Classification by MCV
Microcytic (MCV < 80 fL)
Small, pale RBCs (hypochromic)
| Cause | Features | Treatment |
|---|---|---|
| Iron deficiency (most common) | Low ferritin, low serum iron, high TIBC, low reticulocytes | PO iron supplementation; identify bleeding source |
| Thalassemia | Normal or high ferritin; often Mediterranean/Asian descent; target cells on smear | Supportive; transfusion for severe; no iron (increases overload) |
| Anemia of chronic disease | Normal or high ferritin; associated with inflammation/infection/malignancy | Treat underlying disease; EPO if renal cause |
| Sideroblastic anemia | High ferritin; ring sideroblasts on bone marrow biopsy; may be drug-induced (isoniazid) | B6 (pyridoxine) for INH-induced; otherwise manage underlying cause |
Nursing: Assess for fatigue, pallor, dyspnea, pica; monitor iron studies (ferritin, serum iron, TIBC); PO iron causes black/tarry stool — educate patient
Normocytic (MCV 80–100 fL)
Normal-sized RBCs; broad differential
| Cause | Features | Treatment |
|---|---|---|
| Acute blood loss | Hematocrit may initially be normal (equilibration takes 4–6 hours); tachycardia, orthostatic hypotension | Control bleeding; volume resuscitation; transfusion if indicated |
| Hemolytic anemia | High bilirubin (indirect), high LDH, low haptoglobin, high reticulocyte count | Identify cause (autoimmune, sickle cell, G6PD); transfusion; steroids for autoimmune |
| Anemia of CKD | Low EPO; associated with renal failure; low reticulocytes | Erythropoietin-stimulating agents (ESA); iron supplementation |
| Aplastic anemia | Pancytopenia (all cell lines low); hypocellular bone marrow | Bone marrow transplant; immunosuppression; transfusion support |
Nursing: Assess for acute bleeding; check reticulocyte count (elevated = bone marrow responding; low = production problem); monitor for hemolysis signs (jaundice, dark urine)
Macrocytic (MCV > 100 fL)
Large RBCs; hypersegmented neutrophils on smear (megaloblastic)
| Cause | Features | Treatment |
|---|---|---|
| B12 deficiency | Neurological symptoms (paresthesias, ataxia, subacute combined degeneration); associated with pernicious anemia, veganism, post-gastrectomy | IM B12 (cyanocobalamin) for pernicious anemia (cannot absorb PO); high-dose PO B12 for dietary deficiency |
| Folate deficiency | No neurological symptoms (key differentiator from B12); associated with alcoholism, pregnancy, malabsorption, methotrexate | PO or IV folic acid; ensure B12 is replaced simultaneously to avoid masking B12 deficiency |
| Alcoholism / Liver disease | Macrocytosis without megaloblastic changes; elevated GGT, AST/ALT | Abstinence; nutritional support |
| Medications | Methotrexate, hydroxyurea, zidovudine, trimethoprim — interfere with folate metabolism | Dose adjustment; leucovorin rescue for methotrexate toxicity |
Nursing: Assess for neurological symptoms (B12 deficiency can cause irreversible neuropathy); pernicious anemia patients need lifelong B12 replacement; check both B12 and folate before supplementing
Platelet Count Reference
| Platelet Count | Classification | Clinical Risk | Nursing Action |
|---|---|---|---|
| < 150,000/μL | Thrombocytopenia | Increased bleeding risk | Identify cause; monitor for bleeding signs; assess for HIT if on heparin |
| < 100,000/μL | Moderate thrombocytopenia | Significant bleeding with trauma | Bleeding precautions; avoid IM injections; use smallest gauge needle |
| < 50,000/μL | Severe thrombocytopenia | Surgical bleeding risk; hold elective procedures | Apply pressure 5–10 minutes after sticks; notify provider before any invasive procedure |
| < 20,000/μL | Critical thrombocytopenia | Spontaneous bleeding risk (petechiae, epistaxis, intracranial) | Strict bleeding precautions; electric razor only; soft toothbrush; no rectal temps or suppositories; fall precautions |
| > 400,000/μL | Thrombocytosis | Usually reactive (not clot risk unless essential thrombocythemia) | Identify cause (iron deficiency, infection, inflammation, splenectomy) |
| > 1,000,000/μL | Extreme thrombocytosis | Thrombosis risk with myeloproliferative disorders | Monitor for clot signs; hematology consultation for essential thrombocythemia |
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with Standard laboratory reference ranges · Clinical & Laboratory Standards Institute (CLSI). It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →