Automation of the prothrombin time assay on a centrifugal analyser using two different chromogenic substrate reagents.

Methods employing chromogenic substrates for the photometric determination of prothrombin time have several advantages over conventional coagulometric methods. We evaluated the analytical qualities of two recently introduced reagents for the photometric determination of prothrombin time. The assays were performed on a centrifugal analyser. Both reagents showed good precision, even with sample volumes of 10 microliters or 12 microliters. The stability of the reagents during storage was investigated at 4 degrees C, 25 degrees C and 37 degrees C. The chromogenic reagent, which contains thromboplastin from human placenta, was compared with a coagulometric method, which includes ox-brain thromboplastin: coagulation activities calculated from International Normalized Ratio values showed good correlation and conformity over the whole test range. The other chromogenic reagent contains thromboplastin from rabbit brain; outside the therapeutic range for oral anticoagulation the results obtained with this reagent showed poor agreement with those obtained with the coagulometric method. Both chromogenic reagents were sensitive to reduced concentrations of coagulation factors of the extrinsic pathway and nearly insensitive to low factor IX concentrations. The results of the photometric test paralleled those of the clotting method during oral anticoagulation therapy.

Seasonal variation of cortisol plasma levels in depressives.

There is some evidence for a seasonal variation of plasma cortisol levels after administration of dexamethasone in depressed subjects. This variation is suspected to be associated with similar season-related changes in pre-dexamethasone cortisol levels. Therefore, cortisol plasma levels in depressed subjects before and after dexamethasone administration were investigated. No seasonal variation was found in pre- or post-dexamethasone cortisol levels.

The 24-hour pattern of urinary MHPG excretion in depressives and normals.

The 24-h pattern of urinary 3-methoxy-4-hydroxy-phenylglycol (MHPG) was studied in 15 depressives and 15 healthy controls. MHPG was measured at 3-h intervals over two consecutive 24-h periods. The shape of the MHPG excretion pattern of the depressed group was different from that of the control group. However, both the consistency and shape of the individual 24-h MHPG patterns exhibited a high interindividual variability. Therefore it is difficult to speculate on a circadian phase difference between depressives and healthy controls. Major factors that may have influenced our results are discussed.

Performance of a three-part dif impedance cytometer (Sysmex E-4000) in comparison with a cytochemical cytometer (Technicon H 6000).

Particle-size analysis of leukocytes with cytometers based on the impedance method makes it possible to distinguish three types of white cells in blood (small cells, medium-sized cells and large cells). In order to test the ability of such a three-part dif cytometer to screen for abnormal cells of the leukocyte series, we assayed the differentiation of white cells in 786 blood samples with the Sysmex E-4000 and compared the results with those of the Technicon H6000, a cytochemical cytometer. The small cell and large cell fractions of the Sysmex E-4000 correlated very well with the percentages of lymphocytes and neutrophils measured with the Technicon instrument and showed good sensitivity and specificity in discriminating samples with normal and abnormal results. The percentage of the medium-sized cells correlated significantly with the contents of eosinophilic, monocytic and basophilic cells as assayed with the Technicon H6000; but for a satisfactory determination of each of these cell lines (sensitivity of more than 90% and ca. 70% specificity) it was necessary for them to represent more than 10% of the medium-sized cell population. The red cell parameters of both cytometers were compared in 695 samples. All parameters, which were not based on measurement of the red cell volume, exhibited an excellent agreement for both instruments.(ABSTRACT TRUNCATED AT 250 WORDS)