| Subject | Contents |
| Definition | A test that measures the total amount of hemoglobin in the blood. Hemoglobin is almost always ordered as part of the CBC ( complete blood count ). (See also Hemoglobin electrophoresis .) |
| Alternative Names | Hgb; Hb |
| How the test is performed | Adult or child: Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding . Infant or young child: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding. |
| How to prepare for the test | Adults: No special preparation is necessary. Infants and children: The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:infant test or procedure preparation (birth to 1 year) toddler test or procedure preparation (1 to 3 years) preschooler test or procedure preparation (3 to 6 years) schoolage test or procedure preparation (6 to 12 years) adolescent test or procedure preparation (12 to 18 years) |
| How the test will feel | When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed | Hemoglobin is the protein which carries oxygen in the blood, and it is contained in red blood cells. Abnormalities of the hemoglobin value indicate defects in red blood cell homeostasis (balance). Both low and high values can indicate disease states. |
| Normal Values | Hemoglobin (varies with altitude): Male: 13.8 to 17.2 gm/dl Female: 12.1 to 15.1 gm/dl Note: gm/dl = grams per deciliter |
| What abnormal results mean | Low hemoglobin values may indicate: anemia (various types) erythropoietin deficiency (secondary to renal disease ) hemolysis (red blood cell destruction) associated with transfusion reaction hemorrhage ( bleeding ) lead poisoningmalnutrition nutritional deficiencies of iron, folate , Vitamin B12 , Vitamin B6 overhydration High hemoglobin may indicate: congenital heart diseasecor pulmonalepulmonary fibrosispolycythemia vera increased RBC formation associated with excess erythropoietin Additional conditions under which the test may be performed: anemia of chronic diseaseclinical hemoglobin Cdiabetesgiant cell (temporal, cranial) arteritishemolytic anemia due to G6PD deficiencyinsulin-dependent diabetes mellitus (IDDM)idiopathic aplastic anemiaidiopathic autoimmune hemolytic anemiaimmune hemolytic anemiairon deficiency anemiaparoxysmal cold hemoglobinuria (PCH)paroxysmal nocturnal hemoglobinuria (PNH)pernicious anemiaplacenta abruptiopolymyalgia rheumaticarhabdomyolysissecondary aplastic anemiadrug-induced immune hemolytic anemia This test may be performed under many conditions and in assessment of many diseases. |
| What the risks are | excessive bleedingfainting or feeling light-headed hematoma (blood accumulating under the skin) infection (a slight risk any time the skin is broken) multiple punctures to locate veins |
| Special considerations | Hemoglobin (Hb), the main component of red blood cells, is a protein that carries oxygen away from the lungs and CO2 back to the lungs. A molecule of hemoglobin consists of 2 pairs of peptide (alpha and beta globins) chains and 4 heme groups, each with 1 atom of ferrous iron. At an oxygen tension (pressure) of 100 mmHg in the pulmonary (lung) capillaries, 95 to 98% of the Hb is combined with oxygen. In the peripheral tissues, where the oxygen tension may be as low as 20 mmHg, the oxygen readily dissociated from Hb and less than 30% of the oxygen remains combined with Hb. (See also serum hemoglobin .) Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. |
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