CPT code 82728 refers to a diagnostic laboratory test used to quantify the level of ferritin in a patient's serum or plasma. Ferritin is a high-molecular-weight protein, primarily found inside cells, that serves as the major reservoir for iron storage within the body. While the vast majority of ferritin is located intracellularly within the liver, spleen, and bone marrow, a small but proportional amount circulates in the blood, making it an excellent and non-invasive biomarker for total body iron stores. A ferritin test is clinically vital for distinguishing between iron-deficiency anemia and anemia of chronic disease. In cases of iron deficiency, ferritin levels are typically the first to drop, often well before changes in hemoglobin levels or red blood cell morphology occur, making it a highly sensitive indicator of early-stage iron depletion. Conversely, significantly elevated ferritin levels can indicate iron overload conditions such as hereditary hemochromatosis or complications from frequent blood transfusions. However, clinicians must interpret elevated ferritin results with caution because the protein also functions as an acute-phase reactant. This means that ferritin levels can rise significantly during periods of systemic inflammation, acute infection, chronic kidney disease, malignancy, or liver damage, regardless of the patient's actual iron stores. The laboratory assay is typically performed using an automated immunoassay platform employing techniques such as enzyme-linked immunosorbent assay (ELISA) or chemiluminescent immunoassay (CLIA). By measuring the concentration of ferritin, healthcare providers can monitor the efficacy of iron supplementation therapy, evaluate patients presenting with chronic fatigue or unexplained anemia, and screen for various metabolic disorders involving iron homeostasis.