Normal hemoglobin variants are embryonic hemoglobins (Gower I, Gower II, and Portland), fetal hemoglobin (Hb F), adult hemoglobin (Hb A), and Hb A2.They differ from each other in the type of polypeptide chains.
INDICATION FOR HEMOGLOBIN ESTIMATION
(2) Screening for polycythemia: Polycythemia refers to increased hemoglobin level above the normal range. It may be primary, secondary, or relative.
(3) To assess response to specific therapy in anemia.
(4) Estimation of red cell indices (along with packed cell volume and red cell count) i.e. mean cell hemoglobin and mean cell hemoglobin concentration.
(5) Selection of blood donors.
METHOD FOR ESTIMATION OF HEMOGLOBIN
(1) Colorimetric methods: In these methods, color comparison is made between the standard and the test sample, either visually or by colorimetric methods.
• Visual methods: Tallqvist chart, Sahli’s acid hematin method, and WHO hemoglobin color scale.
• Photoelectric methods: Cyanmethemoglobin (hemiglobin-cyanide) method, oxyhemoglobin method, and alkaline hematin method.
(2) Gasometric method: Oxygen carrying capacity of blood is measured in a Van Slyke apparatus. The amount of hemoglobin is then derived from the formula that 1 gram of hemoglobin carries 1.34 ml of oxygen. However, this method measures only physiologically active hemoglobin, which can carry oxygen. It does not measure carboxyhemoglobin, sulfhemoglobin, and methemoglobin. Also, this method is time-consuming and expensive. The result is about 2% less than other methods.
(3) Chemical method: Iron-content of hemoglobin is first estimated. Value of hemoglobin is then derived indirectly from the formula that 100 grams of hemoglobin contain 374 mg of iron. This method is tedious and time-consuming.
(4) Specific gravity method: A rough estimate of hemoglobin is obtained from the specific gravity of blood as determined from copper sulphate technique. This method is useful in mass screening like selection of blood donors. See Procedure.
Tallqvist hemoglobin chart consists of a series of lithographed colors said to correspond to hemoglobin values ranging from 10 to 100%. A drop of blood obtained by finger puncture is placed on a piece of absorbent paper. Color produced is matched against the color on the chart and corresponding reading is taken. Although this method is cheap and simple, margin of error is 20-50%.