A New Method of Determining Plasma Fibrin

Abstract

The usual method of estimating the fibrinogen content of the blood is by recalcifying the oxalated plasma in order to convert the fibrinogen into fibrin. The quantity of fibrin precipitated is then determined by the Kjeldahl, the gravimetric, the colorimetric, or the refractometric methods. The method of determining plasma fibrin presented here is based on the coagulant activity of certain types of snake venom. Martin was the first to demonstrate the striking activity of the venoms of certain Australian snakes in causing coagulation of blood both in vivo and in vitro. Lamb found that minute doses of such venoms could also coagulate in vitro blood which had lost the capacity for spontaneous coagulation on account of the addition of citrates, oxalates or fluorides. Among the venoms noted for their coagulating action are those of the following snakes: Notechis scutatis (tiger snake), Pseudechis porphyriacus (black snake), Echis carinata (phoorsa) and Viperi russelli (daboia). The former 2 species are found in Australia and the latter 2 in India. In addition, certain species of the Lachesis group of vipers are known to exhibit this property. In the present investigation, tiger snake venom, which apparently has the most powerful coagulating action, was used. In all probability, the venoms of the other species mentioned can also be used. The actual technique of estimating the concentration of fibrinogen (as fibrin) in the plasma with the aid of tiger snake venom is as follows: One cc. of oxalated plasma is diluted 25 to 30 times with normal saline solution. (The quantity of powdered potassium oxalate used for collecting the blood need not be accurately measured.) To the diluted plasma is added 0.3 cc. of a 1 to 5,000 dilution of dried tiger snake venom in normal saline.