Osmotic fragility of the RBCs Enas Sabah MSc. Human Physiology

Shape and of Red Blood Cells. Normal red blood cells are biconcave discs, but the shapes of red blood cells can change remarkably as the cells squeeze through capillaries. because the normal cell has a great excess of cell membrane for the quantity of material inside, deformation does not stretch the membrane greatly and, consequently, does not rupture the cell.

Osmotic fragility It is defined as the ease with which the cells are broken down in hypotonic solutions. It is expressed in terms of concentration of saline solutions in which cells are hemolysed. The osmotic fragility test is often performed to aid with diagnosis of diseases associated with RBC membrane abnormalities.

Osmotic Pressure and Tonicity  Osmosis is the movement of water molecules through a semipermeable  membrane from a region of high water concentration to low water concentration is called osmosis that tends to equalize the concentrations of solute on the two sides of the membrane. Osmotic pressure its the pressure that would be required to stop water from diffusing through a semipermeable  by osmosis. Tonicity is the measure of this pressure.

Procedure: Take 8 small test tubes and keep them in a rack. Put 5 ml of different saline concentrations (0.9%, 0.7%, 0.6%, 0.55%, 0.45%, 0.35%, 0.3%, and 0.2%) to their corresponding labeled test tubes. Draw 1 ml of blood and then put exactly equal drop of blood to inside each test tube. Shake each test tube gently to mix the blood with the solution. Spin the test tubes inside the centrifuge at around 10000 RPM for 5 minutes. Find the value at which the hemolysis is just starting and the value at which the hemolysis is complete.

Normally hemolysis begins between 0. 55-0 Normally hemolysis begins between 0.55-0.45% saline solutions and becomes complete at around 0.35%. The indicator of partial hemolysis is turning of colour of the solution to red in addition to deposition of part of the cells in the bottom of the test tubes. Complete hemolysis is indicated by red-colored solution without any deposition.

Fragility of erythrocytes increases in: hereditary spherocytosis glucose-6-phosphate dehydrogenase (G6PD) deficiency. Note: when we said that fragility of RBCs increase that’s mean break down of RBCs increase.

Hereditary spherocytosis The disorder is caused by mutations in genes relating to membrane proteins. The abnormal erythrocytes are spherical rather than the normal biconcave disk shaped, this abnormal shape interfere with the cell's ability to be flexible to travel from the arteries to the smaller capillaries. This difference in shape also makes the red blood cells more prone to rupture.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency G6PD deficiency is a genetic abnormality that results in an inadequate amount of glucose-6-phosphate dehydrogenase (G6PD) in the blood and occurs almost in males. The inherited disorder caused by a genetic defect in the red blood cell (RBC) enzyme G6PD, protects RBCs from oxidative injury. Some people may develop symptoms when they’re exposed to the medication, food, or infection that triggers the early destruction of red blood cells. Once the cause is treated or removed, symptoms of G6PD deficiency usually relieve.