Abnormal hemoglobin levels can be caused by various conditions. Low hemoglobin may indicate anemia, which can result from nutritional deficiencies such as iron, vitamin B12, or folate deficiency, chronic diseases, or bone marrow disorders. High hemoglobin levels might suggest polycythemia vera, a condition where the bone marrow produces too many red blood cells, or it may be a response to low oxygen levels in the blood, often seen in smokers or individuals living at high altitudes.
