Clinical Chemistry, Vol 8, 80-90, Copyright © 1962 by the American Association for Clinical Chemistry

A Graphic Prothrombin Time Recorder with Air Bath

¹ Department of Physiological Chemistry and the Clinical Chemistry Laboratory, Temple University Medical Center, Philadelphia, Pa.

An air bath is described which maintains plasma, reagents, and glassware at constant temperature. Within this bath is a variable light source, without filters, from which light passes through the liquid mixture of plasma and reagents (0.3-ml. volume) to a photoelectric cell. The output of the cell is fed into a Speedomax recorder. Addition of reagents and time of clotting show clearly on the record, and specimens can be run through the instrument at the rate of one to two per minute. Prothrombin time is determined by measurement between points on the recorded curves.

The instrument has been in continuous use at Temple University Medical Center since 1953. Prothrombin contents check well with those obtained visually in a constant-temperature room. Technologists regard use of the instrument as less fatiguing than the visual method. Results are perhaps more objective.