Hemoglobin, the oxygen carrying pigment of erythrocytes, formed by developing eruthrocytes in the bone marrow, a hemoglobin made up of four different polypeptide globin chains that contain between 141 and 146 amino acids. Each erythrocyte contains 200 to 200 molecules of hemoglobin, each molecule of hemoglobin contains four groups of heme, and each group of heme can carry one molecule of oxygen. A is normal adult hemoglobin and hemoglobin F is fetal hemoglobin. Many abnormal hemoglobin have been reported; the first were given capital letters such as hemoglobin E, H, M, and S, and later ones have been named for the place of discovery.
A secondary function of hemoglobin is as part of the blood buffer syste. The histidine residues in the globin chains act as weak bases to minimize the change in blood pH that occurs as oxygen is absorbed and carbon dioxide taken up from the tissues. The normal concentrations of hemoglobin in the blood are 12 to 16 g/dl in women and 13.5 to 18 in men. But in India and developing countries levels are less by about 2g/dl.
Hemoglobin can be estimated by several methods. They include Sahli – Adam’s Method, Dare’s method, Haldane’s method, Talliquist method, Gasometric method, Spectrophotometric method, Automated & non-automated hemoglobinometry, alkaline hematin method, specific gravity, comparator method etc. Acceptable level of hemoglobin for blood donation is 12.5 gm/dl or more, for both male and female donors. And the level should, definitely, not more than 18 gm/dl.
Specific Gravity Method:
The most practical method for the out-door camp is specific gravity method. Copper sulphate solution with a specific gravity of 1.053 is equal to 12.5 gm/dl.
Advantages: Time taken for this procedure is less than 5 minutes. Because of this a large number of donor’s hemoglobin can be estimated. The main advantages is, it is cost effective and would cost less than a rupee per test. It does not require costly equipment and anybody can perform without intense training.
Disadvantages: It is a semiquantitative method. It cannot tell the exact value. If the donor passes the test he has hemoglobin of 12.5 gm/dl or more. And if the donor fails the test he has hemoglobin less than 12.5gm/dl and he cannot donate blood and he is deferred from donation. If the donor is having high levels of hemoglobin say 17 or more, he may be suffering from polychtemia which maybe a precancerous condition and his blood should not be transferred to the patients. So, the main disadvantage is that we may take blood from a polycythemia (diseased) patient because he has passed the test. And, his blood maybe transfused to patients which is not advisable.
Strip/ Cuvette method:
Now a day the blood banks are adapting to strip or cuvette method. Strip or cuvette is precoated with reagents which react with hemoglobin. The resultant color is red by optical method.
The strip method is like a glucometer where the strip is precoated with reagent. A drop of blood is applied over it and the strip is inserted into the hemoglobin reader which reads the reaction and gives hemoglobin value in grams per deciliter within 6 seconds.
The cuvette system consists of a small portable hemoglobin reader and single disposable microcuvettes. The optical eye of the microcuvette contains the dried testing reagents. Ten microliters of blood are drawn into the optical eye by capillary action and spontaneously mixed with the reagents. Hemoglobin is converted to azidemethemoglobin. The HemoCue reader tunes the reaction and displays hemoglobin results in grams per deciliter, within 6 seconds.
Advantages: This method is sensitive and gives a fairly accurate result. The test is less time consuming and each test will take less than 5 minutes. Since it is a quantitative method, patients with polycythemia, who are apparently healthy, can be identified and their blood transfusion to patients is prevented. Another advantage is that equipment has memory for 100-600 results.
Disadvantages: The main disadvantage is the cost. It may cost between 30-70 rupees per test. A costly equipment is required and the technologist require training.
Other methods of estimating hemoglobin is not practical in the out-door setup. And some of them are obsolete. Eg: Sahli’s acid hematin or alkali hematin methods.