In coagulation diagnostics photometric assay procedures are in widespread use. Due
to the availability of new specific chromogenic peptide substrates, automated instruments
play an important role in clinical routine laboratory diagnosis. For research work,
the benefit of expensive industrial photometric coagulation systems is questionable,
especially as the program cannot be adapted by the user. For this purpose we developed
an inexpensive microcomputer-controlled measuring system as well as a suitable photometric
assay which allows to determine chromogenic clotting times with any conventional spectrophotometer.
Absorbance data were taken from the analog chart-recorder output of a double-beam
spectrophotometer, digitized by a 12 bit analog-to-digital converter and read by the
computer via an interface. Menu driven, user orientated / user dialogue based compiled
BASIC software was written to enable data acquisition and processing.
During the chromogenic assay procedure, automatically collected absorbance data were
displayed, stored, analyzed immediately, saved on disk for later kinetic analysis
and printed.
Preliminary results with our chromogenic PT-assay indicate excellent reproducabi1ity
of the test. The clotting time itself is defined as the interval from the beginning
of the test to the moment when a preselected absorbance change occurred. Standard
curves can automatically be calculated by regression routines after measurement of
reference values.
It must be emphasized that the occurence of fibrinogen-generated turbidity during
the chromogenic assay sometimes influences the total absorbance significantly. For
this reason the reaction time has to be limited by a low optical endpoint setting.
