Hemoglobin is the iron-containing protein inside red cells that binds oxygen in the lungs and releases it in the tissues. The measured value is the concentration of that protein in whole blood, so it reports on the oxygen-carrying capacity of the blood rather than on any single organ. It is the central number of the complete blood count and the usual starting point when anemia is being considered.
No readings for this marker yet.
Lowered hemoglobin most often reflects anemia, which itself has many origins: iron, vitamin B12 or folate deficiency, blood loss that may be slow and unnoticed, chronic inflammation or kidney disease, and dilution during pregnancy. Raised values most often follow dehydration, which concentrates the blood, and are also seen with smoking, life at altitude, chronic lung disease, or, less commonly, a bone marrow disorder that overproduces red cells. Neither direction names a cause on its own. A single out-of-range result is a reason to repeat the test and discuss it with a doctor, not a diagnosis.
Hydration status is the main short-term distortion: fluid loss raises the value and fluid overload lowers it, and lying down for a while before the draw can shift it slightly downward. Smoking and altitude raise it chronically, and long-term use of NSAIDs such as ibuprofen, naproxen or acetylsalicylic acid, or of antiplatelet drugs such as clopidogrel, can lower it through gastrointestinal blood loss. It is read alongside hematocrit and the red cell count, and above all with MCV, MCH and RDW, which classify the type of anemia; ferritin and iron studies usually follow.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.