The Normal Blood Clotting Time in the Light of Experience with the "Two-syringe" Technique

Abstract

The surgeon who requests the pathological laboratory to determine a patient's blood clotting time expects a result which will indicate if surgery might be dangerous. If he follows the teaching of Cummine and Lyons (1948) or of Dutton (1954) The work of Allen and Attyah (1953) suggested a possible explanation of these inconsistencies. These workers claimed that, even when a vein was entered with minimal trauma, blood withdrawn into the first syringe clotted sooner than that withdrawn subsequently into a second syringe. Normal medical students were used in their investigations. With large-calibre short tubes (internal diameter 9.5 mm., height 40 mm.) and 10 ml. syringes with 20-gauge needles, they showed that the coagulation time of the blood in the second syringe was significantly longer than that in the first. Each of 10 tubes was filled from the bottom with 1 ml. using an 18-gauge needle, and the whole test was performed in a water-bath at 370 C. The end-point was taken at the time for the blood in the last tube to clot, each being completely inverted at intervals of five minutes. The tubes were examined in the order in which they had been filled. In 96% the clotting time was 20-35 minutes; it was never under 15 or over 40 and the average was 26 minutes. Method of InvestigationThe blood coagulation times of new patients admitted to a large mental hospital were estimated. None of those investigated was physically ill and none gave a history of bleeding after operation. Advantage was taken of the fact that all patients admitted have blood taken for Wassermann and Widal tests, and the coagulation times were determined with these specimens of blood. The patients were not, therefore, inconvenienced. Those with difficult veins were excluded.Test-tubes (not moistened with saline) measuring 3 in. by I in. were filled from the bottom using 10-ml. syringes and 18-gauge needles. Blood was aspirated, with minimal venous trauma, into a syringe, which was then removed and a second one fitted on to the needle, which was maintained as motionless as possible in the vein. Clean needles were placed on each syringe and 1 ml. of blood was put into each tube; in all cases blood from the second syringe was put into 10 tubes, but blood from the first was usually only put into five. When blood appeared in each syringe a stop-watch was started. The tubes were left undisturbed for five minutes and then examined by tilting at intervals of 30 seconds. They were examined in the order in which they had been filled, each succeeding one being left undisturbed until blood in the preceding one had clotted. In taking the specimens suction was never applied until the tip of the needle was inside the lumen of the vein. ResultsAs there is a difference of opinion as to how the coagulation time should be read, results are given both as the average of the tubes and also as that of the last tube.