Hemoglobin is a protein in red blood cells that gives blood its red color. Its primary purpose is to bind oxygen in the lungs and transport it throughout the body. It also carries carbon dioxide from tissues back to the lungs for exhalation. Adequate hemoglobin levels are fundamental for cellular respiration and overall bodily function.
Hemoglobin Measurement and Normal Ranges
Hemoglobin levels are measured as part of a complete blood count (CBC) test. The standard unit of measurement is grams per deciliter (g/dL), indicating the amount in 100 milliliters of whole blood. Automated laboratory machines analyze blood samples for these measurements.
Normal hemoglobin ranges vary based on age, sex, and the specific laboratory. For adult males, a normal range is between 13.5 and 17.5 g/dL. Non-pregnant adult females have levels ranging from 12.0 to 15.5 g/dL.
During pregnancy, a woman’s blood volume increases, diluting hemoglobin concentration and leading to lower values. For pregnant women, a hemoglobin level of 11 g/dL or higher is normal for the first and third trimesters, while 10.5 g/dL or higher is normal for the second trimester. These ranges guide healthcare providers.
Interpreting Abnormal Hemoglobin Levels
Hemoglobin levels outside normal ranges can signal an underlying health condition. Low hemoglobin, termed anemia, indicates reduced blood oxygen-carrying capacity. Symptoms include fatigue, weakness, and shortness of breath, as tissues do not receive enough oxygen.
Conversely, an elevated hemoglobin level is known as polycythemia. This means an abnormally high concentration of red blood cells and hemoglobin in the blood. Symptoms may include headaches, dizziness, and a reddish complexion. Both low and high levels warrant medical evaluation to determine the cause and appropriate action.
Hemoglobin and Blood Transfusions
Hemoglobin levels directly influence blood transfusion decisions. In hospitals, a “unit” often refers to packed red blood cells (PRBCs). PRBCs contain concentrated red blood cells with plasma removed, effectively increasing oxygen-carrying capacity. Transfusions are indicated to correct anemia or compensate for significant blood loss.
For adult patients not actively bleeding, one unit of PRBCs typically raises hemoglobin by about 1 g/dL. This increase is usually measurable within 15 minutes to an hour post-transfusion. However, this increase can vary based on patient body size and ongoing blood loss.