The significance of platelet counts in coagulation studies

Traditionally, the platelet count recommended for coagulation studies has been less than 10 x 10(9)/L, but the documentation for this is obscure. In the present study, platelet rich plasma (PRPs) and platelet poor plasmas (PPPs) were prepared from the same blood specimen to determine prothrombin times (PTs), International Normalized Ratios (INRs), partial thromboplastin times (PTTs), and their results compared. The measurements of all three of these parameters are not statistically or clinically significant in 100 paired comparisons. Incremented platelet count studies, selected by the number of platelets in the PRPs, showed that platelet counts of at least 199 x 10(9)/L, or perhaps even higher, did not compromise the results of PTs, INRs or PTTs. Such increased platelet counts, however, cannot be tolerated in the various studies for antiphospholipid antibodies, the Lupus Anticoagulant (LAC), or when monitoring heparin therapy with PTTs. Here, the < 10 x 10(9)/L platelet levels must be respected; otherwise the tests would be compromised by platelet-liberated phospholipid (Triplett, Brand et al., 1983) or by Platelet Factor 4, respectively.

Modified anticoagulant therapy factor and international normalized ratio in patients in an unstable coagulation state with respect to warfarin therapy

In our pilot study of 1997, an Anticoagulant Therapy Factor (ATF) was formulated, compared to the International Normalized Ratio (INR) and proposed to replace the INR. Statistically, replacement of the INR was reasonable; but many discrepancies occurred when the results of ATFs and INRs were compared for individual patients. The study was based on patients undergoing induction of warfarin anticoagulant therapy, so they were "unstable" with respect to warfarin. A 1998 follow-up study by Carroll and Jackson based on patients "stable" with respect to warfarin, having taken the drug for at least six weeks, was, therefore, undertaken. In this study, the ATF was modified to an MATF by both multiplying the ATF by the prothrombin ratio (PR) and adjusting the INR-ATF linear regression analysis line by analytic geometry, so that the slope was one and the line passed through the origin. These modifications achieved both statistical and individual patient concordance between INRs and ATFs. The purpose of the present paper is to apply the techniques of the 1998 study to the original 1997 pilot study to see if the reprocessed data on the "unstable" patients is, in fact, also concordant with respect to INRs and ATFs.

Warfarin monitoring by an anticoagulant therapy factor (ATF)

In a pilot study (1997) using POTENS+, our coagulation instrument, we determined that: (a) an Anticoagulant Therapy Factor (ATF) was comparable to the International Normalized Ratio (INR) for monitoring warfarin anticoagulant therapy, (b) one could use any of the four thromboplastins with which the ATF was derived with comparable results, and (c) the ATF could be proposed to monitor warfarin therapy. The ATF-INR comparisons correlated well statistically; but when individual ATF-INR comparisons were later studied, there were frequent discrepancies. The pilot study (1997) was based on hospitalized patients, so almost all patients were undergoing induction of warfarin anticoagulation. Since none of them had taken warfarin for at least six weeks, none of them could be considered "stable" on warfarin. In the present study, all patients were on warfarin therapy for at least six weeks, and the ATF equation was modified by multiplying it by the prothrombin ratio (PR) to give a corrected ATF (CATF). This CATF was then further modified to achieve agreement with the INR by adjusting the linear regression line by means of analytic geometry, so that the CATF-INR regression line now had a slope of one and passed through the origin. With these changes, the modified ATFs (MATF) and INRs correlated well and were nearly equal numerically when using two of the four thromboplastins. Reason for the discrepancies with the other two thromboplastins will be discussed.

Warfarin monitoring independent of the international normalized ratio (INR): a pilot study

Warfarin monitoring is extended to include an anticoagulant therapy factor (ATF). ATF is shown, using four different thromboplastins (Tps), to be comparable with the International Normalized Ratio (INR) mathematically; but ATF is less cumbersome and does not have the INR's poor precision with up to 13.5% error. ATF is formulated from the prothrombin time (PT), fibrinogen transformation rate (FTR) (a representation of thrombin activity), and a consideration of the fibrinogen (FBG) content of blood plasma. Each of these three components is derived from the optical density (O.D.) changes during both the monitoring of the PT and the following FBG-fibrin conversion by a potentiophotometer (PTPH), a linear-reading spectrophotometric device. Comparison of the ATF with the INR shows correlation coefficients of 0.9474, 0.9248, 0.8116 and 0.8603 using the four respective Tps, and the difference against the mean for Bland-Altman plots averages only 0.2 units more for the ATF than the INR. The ATF is independent of the Tp used, and, although Tp affects the PTs, Tp essentially only initiates the tissue factor pathway (TFP) (extrinsic clotting system) to then obtain the PT. It has no rapid direct effect on thrombin activity. For these reasons, in ATF determination, the kind of Tp used is of no consequence. The ATF is independent of the INR, and numerically almost equal to it. The ATF is, therefore, proposed as a replacement for the INR.

Rapid fibrinogen determination with the prothrombin time using a potentiophotometer

The potentiophotometer (PTPH) is a spectrophotometric device that embodies the electrical, analog solution to Beer's Law. The output of the instrument gives, directly and simultaneously, the concentration of the substance being measured. The PTPH has been applied to the manual determination of fibrinogen (FBG) with the same thrombopalstin injection as the prothrombin time (PT). We have now semi-automated and computerized the PTPH to constitute the coagulation instrument named POTENS+. POTENS+ determines the FBG rapidly, within approximately three to twenty seconds after the PT. With POTENS+, precision, linearity and reference range will be given for its FBG method. The accuracy of POTENS+ will be assessed by comparing it with both automated FBG methods on the MLA Electra 1000C Coagulation Timer. Of these two methods, the automated Clauss method is used as the reference method.

A semi-micro method for fibrinogen determination essentially unaffected by turbidity

A semi-micro method (BR BLUE) is presented using Coomassie Brilliant Blue G-250 color reagent for the determination of fibrinogen on potentially turbid specimens. It is compared with the reference Clauss method using the automated MLA Electra 1000C Automatic Coagulation Timer and the semi-automated Mechrolab Clot Timer. Correlation is excellent (r = 0.97). The BR BLUE method is also seen to be reasonably precise and linear.

Applications of a new instrument, the potentiophotometer

The Potentiophotometer is a new instrument for measuring the absorption characteristics of solutions. A brief description of its construction and theory of operation is presented, with illustrations of its use in the colorimetric quantitative analysis for inorganic phosphorus and total protein in serum. The potentiophotometric results correlate well (r = 0.97 to 0.98) with measurements made of the same solutions with either of two conventional spectrophotometers, the Gilford 300N and the Coleman Jr. II.

Applications of a new instrument, the potentiophotometer

The Potentiophotometer is a new instrument for measuring the absorption characteristics of solutions. A brief description of its construction and theory of operation is presented, with illustrations of its use in the colorimetric quantitative analysis for inorganic phosphorus and total protein in serum. The potentiophotometric results correlate well (r = 0.97 to 0.98) with measurements made of the same solutions with either of two conventional spectrophotometers, the Gilford 300N and the Coleman Jr. II.

Potentiophotometry

The present derivation relates, in terms of analytical chemical photometry, the theory of operation of an extremely simple instrument which embodies both the electrical analog solution to Beer's Law of Spectrophotometry and the multiplication of this solution by a constant, such that the voltage reading of the instrument is identical to the concentration of the light absorbing substance being measured. Because the raw output of the instrument is both linear and proportionable, calibration of the instrument is accomplished by appropriately setting and positioning the potential difference between two known standard solutions. The determination of the concentration of an unknown solution is then the direct reading of the voltage it generates in the system. This approach to measurement is called Potentiophotometry, because it is based on potentials generated from light.