Estimation of fibrinogen-fibrin related antigen by continuous flow analysis

A precise method for the determination of fibrinogen-fibrin related antigen (FR antigen) in an automated tanned red cell haemagglutination inhibition system is described. In a continuous flow system aliquots of serum are mixed with a dilution of rabbit anti-human fibrinogen serum. The FR antigen neutralizes the anti-fibrinogen serum and on addition of tanned human red cells sensitized with human fibrinogen, the cells agglutinate according to the remaining anti-fibrinogen activity. The agglutinates are removed and the remaining free cells are haemolysed with saponin and the colour measured at 550 nm. The density of the colour formed is in proportion to the amount of FR antigen present. The range in 102 normal males was 4.8 plus or minus 2.4 mug/ml. A significant increase in the levels of FR antigen throughout pregnancy was found, the highest levels being in the latter half of the third trimester. The levels of FR antigen in 31 normal urines was 0.46 plus or minus 0.44 mug/ml.