Hematology Foundations

Blood problems become easier to recognize when the abnormal component is linked to its job. Red blood cells carry hemoglobin, and hemoglobin carries oxygen. A low hemoglobin concentration reduces oxygen delivery to tissues, so the patient may develop fatigue, exertional dyspnea, tachycardia, dizziness, pallor, or reduced activity tolerance. The body may compensate by increasing heart rate and redirecting blood flow. Chest pain, syncope, dyspnea at rest, hypotension, confusion, or declining urine output suggest that compensation is failing. White blood cells defend against infection. The differential matters: neutrophils are especially important for rapid defense against bacterial and fungal invasion, whereas lymphocytes support adaptive immune responses. A low white blood cell count does not automatically mean the same risk in every patient; the type and severity of the deficit, the trend, and the presence of fever determine urgency. Platelets form the initial plug at an injured vessel. Low platelets or impaired platelet function produce mucosal and skin bleeding—petechiae, ecchymoses, epistaxis, bleeding gums, prolonged bleeding from venipuncture, hematuria, or blood in the stool. Plasma contains clotting factors that stabilize the platelet plug. A...