Labs and Diagnostics

A laboratory result is a measurement, not a diagnosis. Its meaning comes from the patient’s symptoms, the timing of collection, the specimen quality, the trend, and the laboratory’s reference interval. A complete blood count (CBC) gives information about oxygen transport, immune response, and haemostasis. A low haemoglobin can reduce oxygen delivery and produce fatigue, pallor, tachycardia, or exertional dyspnoea. A white-cell count may support infection or inflammation, but a normal count does not exclude serious infection, particularly in an immunocompromised patient. Platelet results change bleeding and clotting risk, although the clinical picture and trend matter more than an isolated borderline value. Electrolytes and glucose describe major components of cellular function. Sodium primarily reflects water balance and extracellular osmolality; rapid or severe abnormalities can alter neurologic function. Potassium changes the resting membrane potential of cardiac and skeletal muscle, so a dangerous value may require cardiac assessment even when the patient reports no symptoms. Glucose abnormalities affect brain function and can become emergencies at either extreme. Urea, creatinine, and estimated glomerular filtration help assess renal function and perfusion. They must be interpreted...