Coagulation and Point of Care in Clinical Practice: History

Abstract

The capability of the blood to pass, under specific conditions, from a “liquid” to a “solid” state has attracted the curiosity of man since ancient times. Already the great father of medicine, Hippocrates, in 400 BC, was fully aware of the fact that freshly drawn blood usually clots within minutes. From these preliminary observations, many years passed before researchers were able to pinpoint the actors and mechanisms involved in blood coagulation. In particular, the modern concept of the coagulation process started in the second half of the nineteenth century when Malpighi, in 1886, separated “fibers,” free of red cells and serum, from clotted blood identifying them with a single-lens microscope. In subsequent years, an Estonian physiologist, Schmidt (1852), identified “thrombin” as the agent able to transform fibrinogen into fibrin and also realized that fibrin could not exist as such in the bloodstream. He thought that the amount of fibrin derived from an inactive precursor throughout the action of a specific enzyme appointed as thrombin. Parallel to the discovery of both the coagulation factors and the mechanisms involved in blood coagulation, the necessity was felt to develop tests able to assess the capability of the blood to clot. One of the first attempts, conducted at the end of the 1800s, to evaluate the function of blood coagulation consisted in placing a fix volume of native blood into a glass test tube and recording the time, called “whole-blood clotting time,” that elapsed before a solid clot appeared. Even though many limitations affected the use of this test, it was for many years the only laboratory test able to evaluate the capability of blood to form a clot. In particular, this test was neither reproducible due to the many technical variables that might affect the test (such as the temperature, the size of the glass tube, the number of times that the tube is tilted back and forth during clot formation, and the subjective perception of clot formation) nor sensitive enough to mild factor deficiencies. At the beginning of the 1900s, to overcome some of these limitations, a more robust test called “recalcification time” was developed. The blood was anticoagulated with citrate or oxalate and the plasma, separated by centrifugation, recalcified under standard conditions. The test measured the same clotting factors as the whole-blood clotting time, and the reference interval was still broad (80–250 s), depending on the speed of centrifugation, which made the numbers of residual platelets vary considerably. During the same year (1905), Morawitz [1] proposed the so-called the classic theory of blood coagulation by summarizing the knowledge that had been available at that time. According to his theory, only four substances are involved in coagulation: thrombokinase derived from damaged tissue, prothrombin, fibrinogen, and calcium. Thromboplastin was released into the circulation at the site of tissue damage and reacted with prothrombin in the presence of calcium to form thrombin, which in turn reacted with fibrinogen to form fibrin. By the 1940s, it became clear that other proteins were involved and subsequently many new coagulation factors were reported. A great step forward was the development of simple laboratory tests such as Quick’s one-stage prothrombin time (PT) [2] and the partial thromboplastin time (PTT) [3]. These reproducible and quick tests were essential to assist research workers to screening and diagnosis of coagulation abnormalities. The great ferment that developed in the mid-1950s around the gradual discovery of factors that were involved in clot formation led to contemporary publication in 1964 of “waterfall sequence” by Dave & Ratnoff in“Science” [4] and “coagulation cascade” by MacFarlane in“Nature” [5].