The McGill Physiology Virtual Lab

Blood Laboratory

Red cell fragility > Procedure, continued
  At this point, a calibration curve must be generated. Knowing that 0% hemolysis has occurred in tube #1 (isotonic solution) and that 100% hemolysis has occurred in tube #6 (distilled water), we can plot the linear relationship between % hemolysis and O.D.
You must now determine the %hemolysis for each tube from the calibration curve. Enter OD values below and get the corresponding % hemolysis from the Calibration Curve.

You also need to calculate the osmolarity of each solution in order to later on plot the % hemolysis versus the osmolarity.

How do I calculate osmolarity?

1M solution of NaCl: 58.5 g/L

0.9 g% NaCl corresponds to 9 g/L of NaCl

Tube # NaCl g/100ml Osmolarity Osmols/l
1 0.9
2 0.6
3 0.5
4 0.4
5 0.3
6 0.0

The Osmotic Fragility Curve


Given the following OD values and your calculated osmolarity and % hemolysis for test tubes #1 to #6, how would you draw the osmotic fragility curve?. Try to trace it in the area to the left (your trace will appear blue). Once you are done, click on the "Done" button, and the correct answer will be displayed in a new window. 




%Hemolysis Osmolarity
1 0.9 0    
2 0.6 0.05    
3 0.5 0.45    
4 0.4 0.48    
5 0.3 0.49    
6 0.0 0.5    

The osmotic fragility test is designed to give some information on the capacity of the red cell membrane to withstand increasing internal pressures brought about by the diffusion of water into the cell.

Questions to think about:

  • what would be the significance of a shift to the right- or to the left- of the osmotic fragility curve?
  • how would the shape of the erythrocyte (sickle cells vs. normal erythrocytes), its surface area to volume ratio (biconcave shape vs. spherocyte) shift the osmotic fragility curve?

To continue with the next section, ESR, click here