2 Hematology and Coagulation

What blood tests measure

A Complete blood count (CBC) includes red-cell measures, white blood cell count, and platelet count. A differential provides counts or percentages of white-cell types. PT/INR and aPTT assess different parts of the coagulation system.

Adult reference ranges vary by laboratory, age, sex, pregnancy, and other factors. Use the range printed on the patient’s report and compare results with the patient’s baseline and clinical condition.

Red-cell measures and anemia

Low Hemoglobin and Hematocrit indicate anemia. Hematocrit often changes in the same direction as hemoglobin, but interpret both alongside hydration and clinical findings. High hemoglobin may suggest dehydration or increased red-cell production.

Mean corpuscular volume (MCV) helps classify red-cell size. A low MCV indicates microcytosis, often associated with iron deficiency; a high MCV indicates macrocytosis, which may occur with vitamin B12 or folate deficiency, liver disease, or other causes. A pattern alone does not establish the cause.

For example, hemoglobin of $8.4\,\mathrm{g/dL}$, hematocrit of $27\%$, and MCV of $70\,\mathrm{fL}$, with fatigue and shortness of breath on exertion, indicate microcytic anemia. Assess vital signs, symptoms, history, and evidence of bleeding; promptly report significant symptoms or suspected active blood loss.

A hemoglobin value alone does not determine the need for transfusion. For most hemodynamically stable hospitalized adults, guidelines support considering transfusion around hemoglobin below $7\,\mathrm{g/dL}$; clinical context and exceptions guide decisions.

White blood cells and infection risk

White blood cell counts may be high or low with infection, inflammation, medications, or marrow and immune disorders. A common adult reference range is about $4{,}000\text{–}11{,}000/\mu\mathrm{L}$. An elevated count does not diagnose sepsis by itself, and a normal or low count does not rule out serious infection.

The Absolute neutrophil count (ANC) is more informative than total WBC for estimating neutropenia-related infection risk. An ANC below $500/\mu\mathrm{L}$ is severe neutropenia. Fever may be the only clear sign of infection in this situation.

For example, a patient receiving chemotherapy with WBC of $1{,}000/\mu\mathrm{L}$, ANC of $300/\mu\mathrm{L}$, and temperature of $38.3\,^{\circ}\mathrm{C}$ ($100.9\,^{\circ}\mathrm{F}$) needs prompt assessment and immediate notification of the responsible clinician or team, following the febrile-neutropenia protocol. Do not wait for another CBC or for the fever to resolve; urgent evaluation and treatment may be expected under local protocol.

A suspected infection with WBC of $15{,}000/\mu\mathrm{L}$, heart rate of $118/\mathrm{min}$, new confusion, and blood pressure of $86/52\,\mathrm{mmHg}$ signals possible deterioration. Hypotension and new confusion require prompt escalation through the facility’s urgent escalation or sepsis pathway while assessing and monitoring the patient; do not wait until the next day to repeat the CBC.

Platelets and bleeding

A common adult platelet reference range is about $150{,}000\text{–}400{,}000/\mu\mathrm{L}$. Low platelets increase bleeding risk, while high values may be reactive or related to a blood disorder. Spontaneous bleeding becomes more likely at very low counts, although risk varies with the patient and the cause.

For a platelet count of $18{,}000/\mu\mathrm{L}$ with new petechiae and bleeding while brushing teeth, assess for active or hidden bleeding, institute bleeding precautions, and promptly notify the clinician or team. Check for neurologic changes, severe headache, blood in urine or stool, and persistent mucosal bleeding. Avoid trauma and medications that increase bleeding risk unless specifically directed. Follow orders and local policy for repeat testing or treatment.

Coagulation tests and anticoagulants

PT is often about $11\text{–}13.5$ seconds, and INR is about $0.8\text{–}1.1$ when a person is not taking warfarin; aPTT is often about $25\text{–}35$ seconds, but is method-dependent. Use the laboratory’s reference range and interpret results in light of the test’s indication. Prolongation may reflect anticoagulant effect or a clotting-factor problem.

A high INR means blood is taking longer to clot and may indicate increased bleeding risk. If a patient taking warfarin has INR of $5.2$ and a nosebleed that will not stop, promptly assess bleeding and vital signs, then notify the responsible clinician or team for urgent direction. The intended INR range depends on the reason for warfarin use. Do not independently change or administer doses; follow orders and the applicable anticoagulation protocol.

For a patient receiving an unfractionated heparin infusion, aPTT above the facility’s therapeutic range with new bleeding at an IV site requires prompt assessment and escalation. Verify the result and infusion details as directed by protocol, contact the clinician or team, and follow authorized orders or the heparin protocol. Therapeutic targets depend on the laboratory and local protocol; do not independently change treatment.

Responding to concerning results

Interpret laboratory results with symptoms, vital signs, trends, medications, and local reference ranges—not as isolated numbers. Low hemoglobin may impair oxygen delivery; low ANC raises infection risk; low platelets and prolonged coagulation tests may increase bleeding risk.

For critical results or signs of bleeding, infection, or instability, assess promptly, escalate to the appropriate clinician or emergency response, and follow facility policy for confirmation and treatment. Do not independently start, stop, or adjust anticoagulants or transfusions unless an authorized order or approved protocol directs the action.