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Hemoglobin is the main intracellular protein of the red cell, consisting of two pairs of polypeptide chains and four heme groups, each of which contains one ferrous iron atom. Hemoglobin acts by transporting O2 and CO2 between lungs and peripheral tissues. The concentration of hemoglobin is the best measurement of the oxygen-carrying capacity of blood. It is measured as part of the routine complete blood count (CBC). Hemoglobin testing is classically performed by photometric measurement of hemoglobin at a wavelength of 540 nm after conversion to hemoglobin cyanide. Not all hemoglobin tests use this method. The Hemocue System measures hemoglobin in undiluted blood after conversion of hemoglobin to hemoglobin azide. Determination of hemoglobin concentration is useful in the detection of anemia. Many factors can produce hemoglobin fluctuations in the same individual and in a group of individuals. Hemoglobin may decrease as much as 1 gm/dL with bed rest. Changes in fluid balance may affect plasma volume and therefore hemoglobin concentration. Gender and age are responsible for important normal variations. Lower hemoglobin values are seen in childhood. Postpubertal males have higher hemoglobin values secondary to the effects of androgens in erythropoiesis. The differences between the values for men and women disappear in the elderly. Hemoglobin decreases about 1 gm/dL during the 2nd and 3rd trimester of pregnancy. Altitude has a predictable effect with an increase of 1 gm/dL for each 3-4% decrease in arterial oxygen saturation. A heavy smoker may increase his/her hemoglobin level by 0.5 to 1.0 gm/dL. A low value that would be abnormal in one person might be appropriate for another. On the other hand, a value within the reference range may be below normal when specific factors relating to the patient and his environment are considered. Spurious hemoglobin results can be obtained if there is incomplete release of hemoglobin from red cells. High lipid concentrations can interfere with the photometric measurement. Reference range is 13-17 g/dL for men and 12.0 -15.0 g/dL for women. Hb levels below 6.0 g/dL are considered critical values. Specimen requirement is one 5 mL lavender top (EDTA) tube of blood. |
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