2 Hematology and Coagulation Laboratory Values

CBC measures and reference intervals

A Complete blood count (CBC) measures red blood cells, white blood cells, platelets, hemoglobin, hematocrit, and red-cell indices. These results help assess oxygen-carrying capacity, infection or marrow response, and hemostasis. A CBC alone does not establish a diagnosis.

Reference intervals are approximate, not universal cutoffs. They may vary by laboratory and may also depend on age, pregnancy, sex, altitude, and clinical context. Use the range printed on the patient’s report and interpret results alongside symptoms and trends.

Common adult reference intervals

• White blood cells (WBC): approximately $4{,}500\text{–}11{,}000/\mu\text{L}$. A high count may occur with infection, inflammation, stress, or other causes. A low count may reflect medication effect, marrow suppression, or other causes; infection risk depends especially on the absolute neutrophil count (ANC).

• Hemoglobin: approximately $12\text{–}16\,\text{g/dL}$ in adult women and $13\text{–}18\,\text{g/dL}$ in adult men. A low value may occur with anemia or blood loss, among other causes. A high value may reflect dehydration or increased red blood cell production.

• Hematocrit: approximately $36\text{–}48\%$ in adult women and $40\text{–}55\%$ in adult men. It often changes in the same direction as hemoglobin. A low result may indicate anemia or blood loss; a high result may reflect dehydration or increased red blood cell concentration.

• Platelets: approximately $150{,}000\text{–}400{,}000/\mu\text{L}$. A low count can increase bleeding risk, especially as it falls or if active bleeding is present. A high count may be associated with increased clotting risk, depending on its cause and context.

• Mean corpuscular volume (MCV): approximately $80\text{–}100\,\text{fL}$. A low, microcytic value can occur with iron deficiency or thalassemia. A high, macrocytic value can occur with vitamin B12 or folate deficiency and other conditions.

Recognizing anemia and infection

Anemia means reduced oxygen-carrying capacity and is commonly reflected in low hemoglobin. Assess for fatigue, pallor, dizziness, shortness of breath, tachycardia, chest discomfort, and signs of blood loss. A rapid decline, symptoms at rest, hemodynamic changes, or suspected active bleeding needs prompt clinical assessment. Do not judge severity from a single number alone.

A high WBC can support concern for infection, but it does not prove infection; a normal WBC does not rule infection out. Assess temperature, vital signs, mental status, and possible infection sources. In patients with low neutrophils, infection may become serious quickly and typical signs may be muted. Treat fever in a patient with known or suspected neutropenia as urgent and follow the organization’s escalation pathway.

Thrombocytopenia and bleeding precautions

A low platelet count can impair formation of the initial platelet plug. Assess for petechiae, new bruising, gum or nose bleeding, blood in urine or stool, heavy menstrual bleeding, persistent bleeding from puncture sites, and new severe headache or neurologic change. The urgency depends on the count, how quickly it fell, the cause, medications, planned procedures, and whether bleeding is present.

For a patient at increased bleeding risk, follow the individualized care plan and facility policy. Common precautions include avoiding unnecessary needle sticks and trauma, applying prolonged pressure after venipuncture, using a soft toothbrush and electric razor when appropriate, and checking before giving medicines that increase bleeding risk. Do not independently stop or change prescribed medicines; promptly clarify concerns with the appropriate clinician. Uncontrolled bleeding or signs of possible internal bleeding require immediate escalation.

Coagulation tests and clinical assessment

Coagulation reference intervals are illustrative and assay-dependent. Interpret results against the laboratory’s range and the patient’s treatment plan.

• Prothrombin time (PT) is often approximately $11\text{–}13.5\,\text{s}$; INR is commonly approximately $0.8\text{–}1.1$ without warfarin. PT/INR assesses the extrinsic and common clotting pathways and is used to monitor warfarin. A high INR means slower clot formation and greater bleeding concern. A low INR during warfarin therapy may mean less protection from clots. The prescribed INR goal depends on the indication.

• Activated partial thromboplastin time (aPTT/PTT) is often approximately $25\text{–}35\,\text{s}$ when the patient is not receiving anticoagulant therapy. It assesses the intrinsic and common pathways and may be used to monitor unfractionated heparin. A prolonged result can reflect anticoagulant effect or other causes.

Monitoring targets and action thresholds for anticoagulants must follow the specific order and local protocol. A prolonged clotting time can signal bleeding risk, but does not by itself diagnose bleeding. Assess for bruising, mucosal bleeding, blood in urine or stool, and bleeding at lines or wounds when PT/INR or aPTT is unexpectedly prolonged. Also assess for possible clot symptoms, including unilateral leg swelling or pain, sudden shortness of breath, chest pain, or new neurologic symptoms, and escalate urgently. A clotting test result alone does not establish whether a patient is bleeding or clotting.

Responding to critical findings

Critical-value thresholds are set by the laboratory and facility; they are not identical everywhere. A result flagged as critical, a major unexpected change, or a concerning result paired with clinical deterioration requires prompt action.

1. Assess the patient first. Check airway, breathing, circulation, vital signs, symptoms, mental status, and evidence of bleeding or thrombosis. Activate the emergency response system for acute instability according to policy.

2. Check the result and context. Confirm patient and specimen identifiers, review the trend, relevant medications and treatments, and any specimen-quality concerns. Do not delay urgent care while waiting for a repeat test. Repeat or recollect a specimen when indicated by policy or a clinician, while promptly communicating the original critical result.

3. Notify the responsible clinician promptly. Communicate the value, units, reference range or critical flag, trend, and focused assessment. Use a structured format such as SBAR and confirm the plan. Follow the escalation chain if the response is delayed or the patient worsens.

4. Use read-back and document. For a verbally reported critical result or order, record the information and repeat it back as required by policy. Document the notification, time, recipient, assessment, instructions, actions taken, and patient response.

5. Continue reassessment. Monitor for changes and carry out authorized orders and relevant facility protocols. Do not independently prescribe treatment or alter anticoagulant therapy.

For example, fever with known neutropenia calls for prompt assessment and the urgent infection-escalation pathway. Low platelets with new petechiae calls for assessment for additional bleeding and prompt notification according to policy. An INR above the prescribed target together with blood in the urine requires prompt assessment and escalation; medication changes require an authorized order or protocol.

• Prothrombin time (PT) / international normalized ratio (INR)

• critical value