Automatic determination of euglobulin lysis time.

Despite the criticisms of substrate variability, the euglobulin lysis time remains a most useful assay of plasma plasminogen activator. It is simple to execute and correlates well with the radioactive clot assay (Sawyer, Fletcher, Alkjaersig, and Sherry, 1960), dilute blood clot lysis time (Fearnley, Balmforth, and Feamley, 1957), and fibrin plate method (Kekwick and Mackay, 1954). It continues to be used in physiological studies of the fibrinolytic system and remains an important activator assay in thrombolytic therapy (Douglas and McNicol, 1964). There are two important sources of error in this method which may account for the variation in resting levels between different laboratories. The first are those procedures which lead to the formation of the euglobulin clot. Blix (1961) has shown that reliable conclusions cannot be made unless blood collection, euglobulin precipitation, and clot formation are carefully standardized. The second source of error lies in the determination of the end-point of clot lysis, which is normally done visually. This subjective assessment of clot lysis has proved to be unsatisfactory on the grounds of accuracy and the uneconomic use of the laboratory worker's time. An automatic device, capable of determining the endpoint of euglobulin clot lysis time with good reproducibility and accuracy, would prove to be a useful instrument to workers in this field. Lackner and Goosen (1959) developed an automatic cine-photographic apparatus which while suitable for whole blood clots was not so for euglobulin clots nor for purified standard clot systems. Nanninga, Zeller, and Maynes (1964) and Newman (1964), using photoelectric systems, described an instrument for investigating purified standard clot systems, but because they required a critical pre-set optical density at which a relay circuit was activated to stop a timing device, these instruments proved to be unsuitable for euglobulin clots. Figure 1 demonstrates the range of optical density, measured in the instrument described below, obtained after complete lysis of 19 different euglobulin clots, prepared simultaneously under identical conditions by the method of Nilsson and Olow (1962). (The zero optical density represents that of distilled water.) These results show that automatic recording of euglobulin