CPT code 85014 refers to the laboratory procedure used to determine the hematocrit (Hct) level in a patient's blood. Hematocrit, often referred to as the packed cell volume (PCV), is a measurement of the percentage of total blood volume that consists of red blood cells (erythrocytes). This measurement is fundamental in hematology and clinical diagnostics because it directly reflects the blood's capacity to transport oxygen throughout the body. The procedure involves the collection of a whole blood sample, typically through venipuncture using a tube containing an anticoagulant like EDTA, or via a capillary puncture (fingerstick). Once collected, the blood is processed either manually using a microhematocrit centrifuge or, more commonly in modern settings, through an automated hematology analyzer. In the manual method, blood in a capillary tube is spun at high speeds, causing the denser red blood cells to pack at the bottom, allowing for a visual measurement of the column of cells relative to the total liquid height. Automated analyzers often calculate the hematocrit value based on the mean corpuscular volume (MCV) and the red blood cell count. Clinically, 85014 is used to diagnose and monitor conditions such as anemia, which is characterized by a low hematocrit, and polycythemia, characterized by an abnormally high hematocrit. It is also an essential tool for assessing a patient's hydration status, as plasma volume changes can concentrate or dilute the RBC population. The test is frequently ordered in emergency departments to evaluate acute blood loss, in surgical settings for preoperative and postoperative monitoring, and in primary care for routine health screenings. The "Rule of Three" is often applied by clinicians, where the hematocrit percentage should be approximately three times the hemoglobin value (in g/dL) in a healthy individual with normal-sized red blood cells. Accuracy in 85014 is vital for determining the necessity of blood transfusions or evaluating the efficacy of erythropoiesis-stimulating agents.