Question

Increasing hemoglobin in the blood increases the density. This is the basis for a simple test that can be used to see if a prospective blood donor has high enough hemoglobin levels to safely donate blood. A drop of blood is placed in a copper sulfate solution and the time for the drop to sink to the bottom is measured. If the time to sink to the bottom is too long, the hemoglobin level is too low. Explain how this test works

Answer 1

Ans. The test is based on following facts-

I. The specific gravity of blood with average Hb content (125. g/ dL) is 1.053 g/mL.

II. If a drop of blood is put on the surface a solution of higher specific gravity (say, 1.100 g/ mL), the blood drop will float on the solution because of being lighter than the liquid.

If the specific gravity of blood drop is greater than that of the solution, the blood drop will sink into the liquid.

III. When put in plain water, the blood drop disintegrates and gets solvated in it. So, we won’t be able to trace the movement of blood drop through the liquid phase.

IV. To make blood insoluble, CuSO₄ solution is used. In this solution, the blood drop forms an insoluble flake by formation of copper-proteinate – a chelated form of blood proteins with Cu. This insoluble complex is stable for 15 seconds, so all measurements must be made within this time frame.

V. So if a drop of blood is carefully put on the surface of a CuSO4 solution of specific gravity of 1.053 g/ mL, the following conclusions can be made-

            1. If blood drop sinks within 15 seconds, it indicates than blood drop has its specific gravity greater than that of solution. In turn, it also means that, the Hb content of blood is greater than 12.5 g/dL (or, 12.5 %). Such result indicates the blood to have sufficient Hb and suitable for donation.

            2. If the blood does not sink within 15 seconds, it indicates that the specific gravity of blood is lower than that of solution due to lower Hb content.

Therefore, if the blood drop does takes longer than 15 seconds, the Hb content of blood is lower than the normal value of 12.5%.