A few milliliters of blood can reveal a great deal. A blood test is any laboratory analysis performed on a blood sample to assess health, diagnose disease, or monitor treatment.

Common panels measure blood counts, electrolytes, kidney and liver function, glucose, lipids, and clotting. Specialized tests detect hormones, tumor markers, infectious agents, or genetic material. Samples are usually drawn from a vein into vacuum tubes that contain appropriate additives.

Results must be interpreted in clinical context; reference ranges vary by age, sex, and laboratory. Abnormal values prompt further investigation rather than automatic diagnosis. Timely blood testing guides transfusion, adjusts medication doses, and detects complications before symptoms appear.

• Laboratory analysis of a blood sample
• Assesses organ function, cells, and disease markers
• Requires correct collection and clinical interpretation
• Used for diagnosis, monitoring, and screening