Clopidogrel-induced platelet inhibition cannot be detected by the platelet function analyzer-100 system in stroke patients

The administration of an adenosine diphosphate (ADP) receptor antagonist, such as clopidogrel, is recommended for recurrent stroke patients under aspirin treatment. However, up to 25% of vascular patients have an inadequate response to clopidogrel treatment, which could be associated with increased reinfarction rates. This study investigated whether the platelet function analyzer (PFA-100) system represents an appropriate tool for monitoring clopidogrel's antiplatelet effects in stroke patients. Sixteen stroke patients on clopidogrel therapy (75 mg/day) were included in a prospective analyst-blinded, cross-sectional study. Platelet function was assayed by collagen/epinephrine (CEPI)- and collagen/ADP (CADP)-induced closure times (CTs) using the PFA-100 system. von Willebrand factor antigen (vWF-Ag) levels were measured by enzyme immunoassay. CEPI-CT and CADP-CT values averaged 160 +/- 15 seconds and 102 +/- 10 seconds, respectively, and were in the normal range. vWF-Ag concentrations averaged 153 +/- 17% and correlated inversely with CTs (r = .71; P < .002 for CEPI-CT, r = .54; P < .04 for CADP-CT). Our data indicate that the current PFA-100 cartridges are not sufficiently sensitive to detect clopidogrel-induced platelet inhibition in stroke patients.

Assessment of PFA-100 system for the measurement of bleeding time in oral surgery

The common diagnostic methods to know primary hemostasis have been classified as invasive, depending on the operator, difficult to reproduce and at times not very reliable. Thus, different systems have been proposed to assess bleeding time, one of them being the PFA-100 device, which we present in this paper.

OBJECTIVE

Compare specificity between the traditional Ivy method with the PFA-100 system to measure bleeding time.

MATERIAL AND METHOD

We obtained a sample of 33 patients between the age of 24-80 years receiving anti-platelet treatment who needed to undergo oral surgery. Bleeding time was obtained by the Ivy method, an INR by an analysis done on the same day and a Coagucheck one hour before surgery as well as measurement of bleeding time with the PFA-100 system.

RESULTS

Mean value of bleeding time through the Ivy method was 406.36 sec.. Mean bleeding time with the PFA-100 system for the collagen/epinephrine cartridge was 226.91 sec. and for the collagen/ADP cartridge was 110.27 sec.. All these values were within normality. We observed very high standard deviations with the Ivy method and more regular ones for the PFA-100 system, indicating its greater specificity. We also obtained a large correlation between collagen/epinephrine cartridge and acetylsalicylic acid.

CONCLUSIONS

We found greater specificity of the analyzer of PFA-100 platelet function for the measurement of bleeding time in relationship with the traditional Ivy method.

Measurement of primary haemostasis using a pressure clamp technique

With the PFA-100 a sensitive and specific screening test for primary haemostasis has recently become available. An important part of the device is a capillary, providing a defined haemodynamic resistance for the perfusion of the aperture. A modified method to measure platelet function (VCP2) is presented in which the capillary essentially is replaced with an 'electronic capillary' by clamping the pressure/flow relationship.

RESULTS AND CONCLUSION

Closure time (CT) and blood volume (BV) as determined by PFA-100 and VCP2 correlated well within (r = 0.922 - 0.952) and between the two methods (r = 0.86). The test variability (CV) of CT could be significantly reduced in the VCP2 method (collagen/epi 3.9 vs. 5.9%, p<0.05; collagen/ADP 3.3 vs. 6.9%, p<0.001), thus considerably increasing test reliability and reducing test variance. In preliminary clinical studies the VCP2 system showed comparable sensitivity for vWD and slightly less sensitivity regarding ASA ingestion. The test spectrum of VCP2 could be extended to more thrombocytopenic samples (< or =20 000/microl) even in combination with low haematocrit levels (20%), thus perhaps permitting the determination of the bleeding risk in bone marrow hypoplasia. Additionally, the sensitivity and applicability can easily be adapted to the desired need only by software modifications.

Evaluation of platelet function with the PFA-100 system in patients with congenital defects of platelet secretion

The template bleeding time is still the screening test for defects of platelet function, although it is an invasive and poorly reproducible technique. The PFA-100 measures platelet function at high shear. Whole blood is aspirated through a capillary to an aperture of a membrane coated with platelet agonists. The system measures the time required to obtain occlusion of the aperture by a platelet plug (closure time). We measured the closure times in the PFA-100 system and the bleeding time in seven patients with delta-storage pool deficiency, 10 patients with "primary secretion defect" (not due to abnormalities of platelet granules or the arachidonate pathway), and 40 controls. Measurements were repeated I and 4 hours after intravenous infusion of desmopressin in six delta-storage pool deficiency and eight primary secretion defect patients. Baseline bleeding time and closure times with the collagen/epinephrine cartridge were longer in delta-storage pool deficiency and primary secretion defect patients than in controls. In contrast, closure times with the collagen/adenosine diphosphate cartridge were normal in both delta-storage pool deficiency and primary secretion defect patients. Treatment with desmopressin increased the plasma von Willebrand Factor levels, shortened the prolonged bleeding time, shortened the closure times with the collagen/adenosine diphosphate cartridge, and normalized the closure times with the collagen/ epinephrine cartridge. Therefore, the PFA-100 test may be a less invasive alternative to the bleeding time in the diagnosis and therapeutic monitoring of patients with platelet secretion defects. The collagen/epinephrine cartridge is more sensitive than the collagen/adenosine diphosphate cartridge to defects of platelet secretion.

[Clinical evaluation of platelet function analyzer PFA-100 in dogs]

The platelet-function-analyzer PFA-100 (Fa. Dade Behring, Liederbach) proofs the capillary in vitro bleeding time by the blood flow through a capillary. The membrane at the end of the capillary is a membrane with a layer of an inductor of the platelet aggregation (collagen/ADP or collagen/epinephrine). The closure time and optional the blood volume flowing out of the capillary can be determined. To find out the applicability of the analyzer for canine blood samples several examinations were carried out in this study. Based on 45 blood samples of clinically healthy dogs a reference range (2.5%- and 97.5% quantile) was defined. Using the collagen/ADP test cartridge the reference range for the closure time was 47-81 s and for the blood volume 223-303 microliters. Using the collagen/epinephrine test cartridge the reference range for the closure time was 67-210 s and for the blood volume 269-611 microliters. In addition, blood samples (n = 19) of dogs with different degrees of thrombocytopenia were examined. Hereby, in contrast to the collagen/epinephrine cartridge, the collagen/ADP cartridge showed a high sensitivity regarding the closure time (n = 18) as well as the blood volume (n = 17). Regarding the results of the healthy dogs and dogs with thrombocytopenia a moderate close correlation was calculated between the in vitro bleeding time and the capillary in vivo bleeding time (rs = 0.590). After intravenous injection of 20 mg/kg acetylsalicylic acid the closure time measured with the collagen/ADP cartridge was 1.3 fold prolonged. The reference range was not exceeded in every case. With artificial variation of the haematocrit a clear prolongation of the closure time at haematocrit values < or = 25% was demonstrated. These results indicate that clinical usability of the platelet function analyzer in dogs is restricted despite its sensitivity to disorders of primary haemostasis.

Development and practical use of the new quantitative bleeding time test apparatus

We have developed a new computerized system for measurement of quantitative bleeding time (QBT) to detect subtle abnormalities of primary hemostasis that are difficult to detect with the standard bleeding time determination. This new apparatus can simultaneously measure the bleeding time (BT; sec), amount of total blood loss (Tv; microl), maximum bleeding rate (Rmax; microl/sec) and bleeding pattern from the bleeding time incision. We have also developed a new holder for the Simplate that enables more consistent incisions and thus improves the reproducibility of the BT test. In this study, the newly developed QBT test was performed in 137 normal healthy volunteers and 10 patients having defined abnormalities of either primary or secondary hemostasis. Comparisons of the standard BT test and our QBT were made in 5 normal subjects and 7 thrombocytopenic patients. Additionally, 6 normal subjects were examined with both tests before and after administration of aspirin. Those results show that our QBT appears to be a more sensitive indicator of primary hemostasis than the standard BT method.

An assessment of human epidermal repair in elderly normal subjects using immunohistochemical methods

The purpose of this study was to document a timetable for selected events of epidermal repair in standard partial thickness incised wounds on the legs of normal elderly human subjects. A Simplate-II bleeding-time device was used for producing the wounds, and immunohistochemical techniques were employed for evaluation of the wounds. Antibodies to filaggrin and Ulex europeus I demonstrated little or no staining on migrating epithelium, but staining was apparent whenever epidermal closure had occurred. Bullous pemphigoid antigen was present in the basement membrane zone at all time points examined, including beneath migrating epithelium, whereas antibodies to laminin and type IV collagen were found only at the most lateral aspects of 2-, 3-, and 5-day wounds. Staining progressed centrally by day 7 and was present as a complete linear band beneath most 14-day wounds. The Simplate-II device provides a standard, easy to use, commercially available, sterile, relatively safe method of producing wounds for systematic studies in humans.

"Haemostasis time", a modified bleeding time test and its comparison with the Duke and Ivy/template bleeding times. I. Normal values, application in thrombocytopenic patients and evaluation of heparin and aspirin effects

The occlusion time ("haemostasis time" - HT) of a thin, short cannula inserted into the cubital vein, was compared with the skin bleeding times of the Duke and Ivy/template techniques. 25 male and 25 female volunteers without a history of bleeding were divided into 5 equally large age groups ranging from 10 to over 50 years of age. They exhibited a range of 46 s-6 min 38 s (95% tolerance interval), while the Duke and Ivy/template bleeding times, which were simultaneously determined, corresponded to values given by other authors. HT is different from the skin bleeding times in that endothelium is replaced by a standard foreign surface which allows better standardization of the method. Similar results were obtained with HT compared to the skin bleeding times. These and a similar, non-significant heparin response with all three techniques suggest that HT is not more influenced by clotting factors than the Duke and Ivy/template bleeding times and, indeed, may be regarded as a bleeding time modification. HT, like both of the skin bleeding times, reflected lowered platelet counts and is even more sensitive in this respect. As tested in a group of 20 male and 20 female volunteers, HT showed a significant prolongation two hours after ingestion of 1 g aspirin. While male individuals exhibited longer bleeding times than females with the Ivy/template technique (sex-related difference p = 0.01), no male to female differences were found both with HT and the Duke bleeding time. HT is easy to perform, inexpensive, leaves no scars and is safe even for the patient with severe bleeding. Moreover, compared to the skin bleeding times, it permits a differential evaluation of vessel wall and tissue effects.

Clinical trial of a new disposable bleeding-time device

A new disposable bleeding time device (Hemalet) was tested in 20 normal individuals and 11 patients with various bleeding disorders. The results were compared with those of Simplate II. The mean bleeding time for normal individuals was 5.4 +/- 1.5 (mean +/- 1 SD) minutes by Hemalet and 5.8 +/- 1.4 (mean +/- 1 SD) minutes by Simplate II, with good correlation between the results by the two devices (r = 0.81). The bleeding time in patients with various bleeding disorders were also comparably prolonged between the two devices. The new disposable bleeding time device with a disposable blade has quick release (penetration) into skin and retraction, and offers an alternative means of a bleeding time test.