To estimate the approximate value of hemoglobin, a method commonly used in blood banks for selecting blood donors is employed. This method is noted for its simplicity and rapid execution.
In this procedure, a drop of the blood sample is allowed to fall from a height of 1 cm into a solution of copper sulfate with a specific gravity of 1.053. This specific gravity corresponds to a hemoglobin concentration of 12.5 g/dl. The blood drop becomes enveloped by copper proteinate and remains separate and distinct for 15-20 seconds. If the blood drop sinks within this time frame, it indicates that the specific gravity of the copper sulfate solution is lower than that of the blood sample, suggesting that the hemoglobin concentration is greater than 12.5 g/dl, thus qualifying the donor for blood donation. Conversely, if the blood drop floats, it indicates a hemoglobin concentration of less than 12.5 g/dl, rendering the sample unsuitable for donation.
However, it is important to note that the concentration of plasma proteins and the total leukocyte count can also affect the specific gravity of whole blood, potentially leading to false-positive results. Conditions such as hypergammaglobulinemia (e.g., multiple myeloma) or leukocytosis (e.g., myeloid or lymphoid reaction, chronic myeloid or lymphocytic leukemia) can result in an inaccurately high hemoglobin level.