A simple method for estimating a 'heparin binding capacity' of human serum.

A method for estimating a 'heparin binding capacity' of human serum is 
described. When human serum is diluted with a low ionic strength, 
heparin-containing buffer at pH 5.5, protein-heparin electrostatic complexes form in solution 
with subsequent formation of insoluble aggregates which can be collected by 
centrifugation. Quantitative determination of the relative amounts by weight of protein 
and heparin in the insoluble heparin-protein aggregates permits estimation of a 
combining ratio at which serum proteins bind with heparin to precipitate 
from solution. This weight combining ratio of protein and heparin is 
a quantitative measure of the total affinity for heparin of all 
proteins in serum which bind heparin at pH 5.57 to form 
an insoluble complex. An unusually high affinity for heparin by an 
abnormal serum protein or an increase in amount of a normally- 
occuring, high heparin-affinity, serum protein would alter the average protein: heparin 
combining ratio and increase the 'heparin- binding capacity' of human serum. 
The converse would be true for serum proteins having a low 
affinity for heparin, lowering the 'heparin-binding capacity' of human serum. The 
described method was used to evaluate the 'heparin-binding capacity' of serum 
proteins in normal individuals and in persons with cystic fibrosis. 