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PubMed1983

Technical considerations for platelet aggregation and related problems.

Platelet aggregation generally is ordered by the physician to evaluate platelet function in hemorrhagic or thrombotic disorders. Malfunction of the platelet may be the result of an intrinsic congenital defect or an acquired problem induced by drugs or certain circulating plasma factors. It is necessary to obtain information from the patient with respect to family history, drug ingestion, physical or mental stress. In addition, other laboratory studies should be obtained to rule out general coagulation disorders affecting the plasma factors. A bleeding time will be helpful in establishing the severity of any platelet dysfunction. Technical considerations with regard to the preparation of the samples are of primary importance in determining platelet aggregation. Aggregating studies require the use of a variety of binding agents. (Studies on shape change, adhesion of platelets, release of platelet granule substance, and or lysis with extrusion of cytoplasmic constituents may be helpful in certain cases.) Instrumentation for platelet aggregation presently is available in many hospitals. The technical factors to be considered for routine aggregation studies include the type and strength of anticoagulant, centrifugation technique used in preparing the platelet-rich and platelet-poor plasma, platelet concentration, time of storage of the sample after venipuncture and after centrifugation, temperature, and the mixing of the sample. In general, critical concentrations of each reagent should be employed to improve the discrimination capability of the assay. Small differences in response may be obliterated by using excessive concentrations of a given reagent. Comparison in response to the test platelets with control platelets is best done at the same time by performing the aggregation in a dual instrument so that handling procedures will be identical and artifactual differences eliminated.

Aging↗
PubMed2001

Does heparin pretreatment affect the haemostatic system during and after cardiopulmonary bypass?

In this clinical pilot study, the influence of heparin pretreatment on the haemostatic system during and after cardiopulmonary bypass (CPB) was investigated. Thirteen patients scheduled for elective coronary artery bypass grafting (CABG) were divided into two groups: heparin pretreated (HP, n = 6) and non-heparin pretreated (NHP, n = 7). Blood samples were taken for measurements of plasma antithrombin-III (AT-III) activity, plasma heparin levels, activated clotting time with (HACT) and without (ACT) heparinase, whole blood platelet function, platelet count, thrombin-antithrombin-III complexes and D-dimer levels. Also, the mediastinal blood loss within the initial 20 h after surgery, and the blood transfusion requirements were monitored. The mean duration of the heparin pretreatment was 55 h (range 24-161 h). There was no significant difference in plasma AT-III activity and platelet count between the groups. Before and after CPB, the platelet responsiveness was better in the NHP group (p < 0.05). The HACT was prolonged in the NHP group during and after CPB compared to baseline values (p < 0.05), whereas, in the HP group, no significant changes were found. Plasma heparin levels and ACT values suggested adequate anticoagulation during CPB. However, the extent of thrombin inhibition and fibrinolysis increased with time on CPB, but did not differ between the two groups. Twenty hours after surgery, the thrombin inhibition showed to be significantly higher in the NHP group. Furthermore, mediastinal blood loss showed a tendency to be lower in the HP group (p = 0.08). However, there was no difference in blood transfusion requirements between the groups. These data suggest that short-term heparin pretreatment affects the perioperative platelet responsiveness and attenuates the consumption of coagulation factors.

Aged↗
PubMed1992

Assessment of whole-blood spontaneous platelet aggregation during pregnancy using an impedance particle counter.

The slide test method of Velaskar and Chitre for determining platelet aggregation in whole blood after induction of aggregation was modified for spontaneous platelet aggregation and evaluated. The reproducibility was satisfactory (CV 1-3%). The results obtained with this method and the method of Velaskar were not significantly different. The Spearman rank correlation was 0.75 (p less than 0.0001). We established reference values for the particle counter method and Velaskar's method in pregnant and non-pregnant women; no significant change in spontaneous platelet aggregation was seen throughout pregnancy. In order to estimate the clinical value of the test in pregnancy, we followed up a number of pregnant patients with primary enhanced spontaneous whole-blood platelet aggregation before and after treatment with low-dose acetylsalicylic acid. The test was found to be suited for the detection of spontaneous whole-blood platelet aggregation and for the follow-up after treatment with acetylsalicylic acid. Further studies are necessary, however, to assess the predictive value of an aberrant test result during pregnancy.

Adolescent↗
PubMed1983

Platelet tests and antiplatelet drugs in coronary artery disease.

This study was designed to clarify discrepancies in the literature concerning platelet survival time and beta-thromboglobulin (beta TG) levels in patients with coronary artery disease (CAD) and the effect of platelet-suppressant drugs on these tests. Platelet survival time and plasma beta TG levels were determined in 48 patients with angiographically documented CAD. The effect of sulfinpyrazone or aspirin/dipyridamole on these measurements was investigated in a double-blind, crossover trial that included a placebo phase. In patients with CAD, the mean plasma beta TG concentration was significantly elevated, but the mean platelet survival time was not significantly different from that in controls. Treatment with sulfinpyrazone or aspirin/dipyridamole did not produce changes in platelet survival time or plasma beta TG concentration that were significantly different from the values during the placebo phase. This study demonstrates that compared with the spontaneous variation in platelet survival time or beta TG concentration, there was no measureable effect of sulfinpyrazone or aspirin/dipyridamole on the results of the tests.

Adult↗
PubMed1983

Antiaggregant effect of indobufen (K3920) measured by the platelet aggregate filtration pressure test (PAFP).

The platelet aggregate filtration pressure test (PAFP) was used to study the aggregant activity of single doses of 200 mg indobufen, administered either orally or by i.v. injection. This double-blind study using placebo in a crossover design was conducted in twelve patients whose baseline aggregation values were high. The compound showed markedly different antiaggregant activity from placebo at the various observation times after administration. The two administration routes did not produce any significant differences. The PAFP test can be useful in identifying atherosclerotic patients with platelet hyperaggregation, and for clinical pharmacology studies with platelet antiaggregant drugs.

Administration, Oral↗
PubMed1988

The degradation of platelet-activating factor in serum and its discriminative value in atherosclerotic patients.

Platelet-activating factor (PAF) is transformed in vivo rapidly into the biologically inactive lyso-PAF. This reaction as well as lipid parameters were quantified in serum from 40 survivors of myocardial infarction and 36 healthy controls matched for age and body weight. The PAF-degrading capacity was 23% (p less than 0.001) higher in patients compared with the control group. Using the degradation of PAF as an univariate discriminator more than 70% of subjects were classified correctly. This is comparable with the discriminatory value of the best lipid variables, apolipoprotein B and HDL-cholesterol. Statistically significant differences in the degradation of PAF were found also by comparing subgroups which were matched for plasma levels of total cholesterol, VLDL/LDL-cholesterol or apolipoprotein B. The ratio by 48% (p less than 0.0001) in the case group was identified as an additional good discriminator between both groups. In contrast, platelet aggregation tests which were performed in acetylsalicyclic acid treated platelet-rich plasma discriminated poorly between patients and controls.

Apolipoproteins↗
PubMed1981

Double-blind study on the activity of plafibride in the treatment of type IV hyperlipoproteinemia.

The effects of a new drug, N-2-(p-chlorophenoxy)-isobutyryl-N'-morpholinomethylurea (plafibride, ITA 104), were studied in a double blind study lasting four months on a group of 30 patients with a type IV hyperlipoproteinemia. In the patients treated with the active drug significant reductions in blood triglycerides were obtained, with a trend to normal. Reduction in blood cholesterol was inconsistent and not significant. As for the lipoproteinogram, a tendency towards a decrease in the pre-beta-lipoprotein fraction was observed and so was a non-significant tendency towards an increase in the alpha- and beta-lipoprotein fractions. Studies on the platelet functioning showed an obvious decrease in platelet aggregation in those patients treated with the active drug. This was very evident for the ADP and adrenaline inductors and rather less significant for collagen. Neither platelet adhesiveness nor aggregation rate changed. Tolerance of the drug was generally excellent. In one patient a decrease in some palpebral xanthelasmas was observed after two months of treatment with the active drug. In only one case there was heartburn and this was corrected with alkalines. In one other case an urticarial rash appeared, but disappeared spontaneously when the drug was temporarily stopped and did not reappear when it was administered again. During the trial no evidence of renal, hepatic or hematological malfunctions were observed. However, a slight tendency towards an increase in the GOT, GPT and LDH was observed, which was not statistically significant. The drug tested may be very useful in the treatment of type IV hyperlipoproteinemia, especially in those forms in which an increase in thromboembolic risk is suspected, either associated with, or secondary to, the actual atherosclerotic disease.

Clinical Trials as Topic↗
PubMed1993

The clinical usefulness of the platelet aggregation test for the diagnosis of heparin-induced thrombocytopenia.

The platelet aggregation test is widely used for the diagnosis of heparin-induced thrombocytopenia (HIT), a potentially serious complication of heparin therapy. We have evaluated its sensitivity and specificity in comparison with those of the 14C-serotonin release test. The sensitivity of the platelet aggregation test was found to vary with the heparin concentration and the donor of the platelets used in the test. The optimal heparin concentrations were between 0.1 and 1.0 U/ml. Using these heparin concentrations, the mean sensitivity varied from 39% (with the least reactive platelets) to 81% (with the most reactive platelets). In comparison, the sensitivity of the release test ranged from 65% to 94%. The specificities of the platelet aggregation test were 82%, 90% and 100% for the following control groups: (1) non-thrombocytopenic patients given heparin, (2) patients with thrombocytopenia due to other causes, and (3) normal controls not given heparin, respectively. The corresponding specificities for the release test was 94%, 90% and 100%. The specificities can be further increased to 100% for all controls with the adoption of a two-point system which defines a positive result as one in which platelet aggregation occurs with a low heparin concentration (0.5 U/ml) but not with 100 U heparin/ml. For optimal results, a two-point platelet aggregation test should be performed with heparin concentrations of 0.5 and 100 U/ml and using platelets of more reactive donors.

Autoimmune Diseases↗
PubMed1999

Inhibition of platelet aggregation after intake of acetylsalicylic acid detected by a platelet function analyzer (PFA-100).

OBJECTIVE: The aim of the investigation was to determine the inhibition of platelet aggregation detected by the platelet function analyzer PFA-100 in patients with coronary artery disease who routinely take 100 mg acetylsalicylic acid once daily. METHOD: The PFA-100 (Dade International Inc., Miami, USA) is a new device for in vitro measurement of platelet function in citrated whole blood. The time needed to form a platelet plug occluding the aperture cut into a collagen/epinephrine- or collagen/ADP-coated membrane is determined under high shear conditions. Typically, acetylsalicylic acid-induced inhibition of platelet aggregation is detected by prolonged closure time in collagen/epinephrine or and normal values for collagen/ADP. Blood samples of 48 patients were investigated, the control group consisted of 10 healthy volunteers without intake of acetylsalicylic acid. The upper limits of normal values of the control group were 137 sec closure time for collagen/epinephrine and 150 sec for collagen/ADP (mean + 2 SD). RESULTS: Statistical analysis (Wilcoxon test) did not show a significant difference (p = 0.46) between the patient group (129 +/- 11 sec) and the control group (92 +/- 7 sec) for collagen/epinephrine (mean +/- SEM). Only 31% of patients had closure time values above those upper limits defined above. CONCLUSION: The effect of 100 mg acetylsalicylic acid daily appears to be too small and too variable to detect a sufficient inhibition of platelet aggregation by the PFA-100 in all patients with coronary artery disease.

Adult↗
PubMed2006

The utility of the PFA-100 in the identification of von Willebrand disease: a concise review.

The PFA-100 (platelet function analyser; Dade-Behring, Marburg, Germany) is a relatively new tool for the investigation of primary hemostasis. Recent studies have shown its utility as a screening tool for investigating various platelet disorders and possible von Willebrand disorder (vWD), both in the initial investigation and in subsequent therapeutic monitoring of desmopressin therapy. This article reviews current findings with respect to the identification of vWD, and highlights both the benefits and the limitations of its clinical utility. In brief, sensitivity to vWD types 2A, 2B, 2M, and 3 is > 98%, but overall sensitivity to vWD (types 1, 2A, 2B, 2M, and 3 combined) is ~85 to 90%. Ultimately, the high sensitivity of the PFA-100 to vWD and its simplicity of use provide its greatest strengths. However, because it is a global test system, and also sensitive to low hematocrit, low platelet counts, and platelet dysfunction (both congenital and acquired; e.g., secondary to medication such as aspirin) it must be recognized that the PFA-100 is neither specific for, nor predictive of, any particular disorder (inclusive of vWD). Nevertheless, used appropriately, the PFA-100 can be considered a worthwhile addition to the hemostasis laboratory involved in the diagnosis or therapeutic monitoring of vWD, and a normal PFA-100 result can be used with some confidence to exclude severe vWD.

Automation↗
PubMed1980

[Limits of platelet aggregation tests for investigating thromboses (author's transl)].

Three methods--spontaneous aggregation, ADP-induced aggregation and levels of circulating platelet aggregates--were used to test for platelet hyperaggregation in 87 adult patients divided into three groups. Group A comprised 26 patients with severe arterial diseases, including cerebral vascular accidents (16) and peripheral thrombosis (10) ; group B consisted of 31 patients with venous conditions, including deep phlebitis (22) and recurrent thrombo-embolic disease (9) ; group C, which served as control, comprised 30 patients with various non-vascular disorders. Spontaneous aggregation and enhanced reactivity to ADP correlated well with each other and were more frequent in patients with vascular diseases. However, one-third of patients in group C had pathological results, while one-third of patients in groups A and B had normal results, independently of any clinical particularity or therapeutic regimen. There were no significant differences between the three groups with regard to circulating platelet aggregates. These tests, therefore, appear to be of statistical and epidemiological interest, but of questionable practical value.

Adenosine Diphosphate↗
PubMed2003

Diagnosis of thrombotic thrombocytopenic purpura based on modulation by patient plasma of normal platelet adhesion under flow condition.

We have designed a simple test for the early diagnosis and treatment monitoring of thrombotic thrombocytopenic purpura (TTP). We examined plasma from 24 TTP patients and normal plasma using a cone and plate(let) analyser (CPA). Test plasma was mixed with citrated normal whole blood (group O) and subjected to flow at a shear rate of 1800/s. Mixing normal plasma (12.5, 25, 50 or 75 microl) with heterologous normal whole blood (final volume of 200 microl) resulted in a decrease of surface coverage (SC, maximally by 63%) and, to a lesser extent, of average size (AS, maximally by 37%) due to dilution of the blood sample. In contrast, mixing the same quantities of acute TTP plasma with normal blood yielded an increase in both SC (up to 125%) and AS (up to 130%). Increased SC and/or AS were detected in all 15 patients in acute phase and in three out of 14 patients in remission. Following repeated plasmapheresis, the enhanced platelet deposition in five patients with acute TTP returned to almost normal patterns. Mixing plasma from patients with other thrombocytopenic conditions in this way resulted in a decrease in both SC and AS, and did not differ from control subjects. In conclusion, the CPA is a simple and specific laboratory test that can be used for the diagnosis and monitoring of plasma exchange therapy in TTP.

Acute Disease↗
PubMed2006

Thromboelastography: potential bedside tool to assess the effects of antiplatelet therapy?

Modified thrombelastography (TEG) is a simple point of care test that provides an overall assessment of ex vivo clot formation and currently has limited clinical application. We evaluated the ability of TEG to assess the effects of antiplatelet therapy on clot formation using a novel assessment parameter (the area under curve). Forty healthy volunteers were divided into four groups of 10. Group A took aspirin 75 mg once daily for 7 days followed by aspirin 75 mg and clopidogrel 75 mg once daily in combination for 7 more days. Blood samples were taken for analysis at day 0 and days 7 and 14. Group B took a single 300 mg dose of aspirin. Group C took 600 mg of clopidogrel only. Group D took 300 mg of aspirin and 600 mg of clopidogrel at the same time. For groups B, C and D blood was taken prior to drug administration and at 2, 6 and 24 h afterwards. Each sample was tested by TEG in four channels following activation using (1) kaolin, (2) activator F (Act F), a direct activator of fibrin, (3) Act F + arachidonic acid (AA) and (4) Act F + adenosine diphosphate (ADP). Parameters measured included the maximum amplitude (MA) of the clot and the area under the TEG-generated curve at 1 h. Significant, time-dependent reductions in MA and area were seen in the AA-activated samples following administration of aspirin in all groups as compared to baseline. By contrast, there were no significant differences in MA or area in the AA-activated samples with clopidogrel alone. Significant reductions were also seen in MA and area in ADP-activated samples from volunteers treated with clopidogrel as compared to baseline. Three out of 10 subjects receiving 600 mg clopidogrel had a reduction in their responses of 30% or less, thus identifying them as relatively resistant to the drug. This study identifies a rapid, reliable method for assessing the time-dependent effects of antiplatelet therapy on clotting using a novel parameter of area of the TEG trace, which could have an important clinical application as a point of care test of efficacy, particularly in the context of acute coronary syndromes and percutaneous coronary intervention.

Adult↗
PubMed1995

[Thrombocyte function of healthy probands taking 50 mg of acetylsalicylic acid per day].

The antithrombotic effect of acetylsalicylic acid (ASS) is attributed in part to its inhibitory action on platelet cyclooxygenase and, thereby, thromboxane A2 (TXA2) formation. The therapeutic goal of low-dose ASS regimens was the development of a preparation showing a high inhibitory capacity on platelet TXA2 generation whilst leaving vascular prostaglandin I2 (PGI2) synthesis unaffected, thereby minimizing side effects. The effect of a new acid-resistant preparation of 50 mg ASS (Thrombo-ASS 50 mg) on plasma levels of ASS, salicylate, TXB2, 11-dehydro-thromboxane B2, serum thromboxane B2 and malonyl dialdehyde, the conversion of exogenous 14C-arachidonic acid to TXB2 and hydroxy-5,8,10-heptadecatrienoic acid (HHT), as well as on the urinary metabolites 2,3-dinor-6-oxo-PGF1 alpha and 2,3-dinor TXB2, were compared in a crossover trial to those of a marketed preparation (Aspirin 100 mg) in healthy volunteers after a single dose and repeated administration of ASS. While platelet activity was inhibited by both the test and the reference substance to a comparable extent, vascular PGI2 production (as determined by urinary 2,3-dinor-6-oxo-PGF1 alpha excretion) was less affected by the test substance. These findings confirm the claim that a dosage of 50 mg ASS administered daily as an enteric coated or uncoated tablet is sufficient to almost completely block platelet cyclooxygenase, while the respective vascular enzyme is only minimally affected.

Adult↗
PubMed1989

Modified bleeding time in the infant.

The present authors developed a modified template bleeding time for use in the newborn infant. The sensitivity of the bleeding time to the presence of antibiotics, indomethacin, generalized illness, and thrombocytopenia was tested in 242 infants. Both indomethacin and thrombocytopenia similarly prolonged the BT, and the latter could be corrected by raising the platelet count.

Anti-Bacterial Agents↗
PubMed2001

Utility of the PFA-100 for assessing bleeding disorders and monitoring therapy: a review of analytical variables, benefits and limitations.

The PFA-100 (platelet function analyser) is a relatively new tool for the investigation of primary haemostasis. Recent studies have shown its utility in monitoring antiplatelet therapy (including aspirin) and as a screening tool for investigating possible von Willebrand disease (vWD) and various platelet disorders. More recently, the PFA-100 has been shown to be of value in monitoring DDAVP therapy in both vWD and platelet disorders. This paper reviews current findings, details the utility of the PFA-100 for some of these purposes, as well as reviewing analytical variables that may complicate the interpretation of results. The author highlights the benefits, as well as noting the limitations, of its use. Ultimately, the greatest strengths of the PFA-100 are its simplicity in use and excellent sensitivity to particular haemostatic disturbances such as vWD, platelet disorders and platelet-affecting medication. However, because it is thus a 'global' test system, this also creates a significant limitation, as the PFA-100 is not specific for, nor predictive of, any particular disorder. However, utilized appropriately, the PFA-100 can be considered a worthwhile addition to any haemostasis laboratory involved in the diagnosis or therapeutic-monitoring of bleeding disorders including vWD and platelet-dysfunctions. This review should be of value to both haemostasis scientists and clinical specialists.

Blood Platelet Disorders↗
PubMed1987

[A modified in vivo platelet retention test in the evaluation of primary hemostasis].

A simple assay system for measuring platelet retention in a standardized superficial skin wound is presented. Platelets were counted in the blood collected at the site of the wound 1, 2 and 3 minutes following incision. Per cent platelet retention was calculated from the difference between venous blood platelet count and wound blood platelet count, divided by venous count. The time course of platelet retention, measured in 20 healthy persons, reflected the sequence of primary and secondary platelet aggregation. Ten patients with congenital platelet defects already showed impaired platelet retention in the early stage of bleeding. On the other hand, administration of aspirin to 10 healthy subjects inhibited only the late stage of platelet retention. In comparison with the template bleeding time our platelet retention test provides additional information useful for evaluating congenital and drug-induced defects in platelet plug formation.

Aspirin↗
PubMed1989

Effect of felodipine, a new calcium channel antagonist, on platelet function and fibrinolytic activity at rest and after exercise.

Fourteen healthy male volunteers (age 21-29 years, mean 23.7 years) were given placebo for 14 days followed immediately by felodipine 5 mg b.d. for a further 14 days. After each period of treatment blood for analysis was taken at rest and after exercise on a cycle ergometer. Platelet aggregation, plasma beta-thromboglobulin (B-TG), platelet factor 4 (PF-4), adrenaline and noradrenaline, and serum thromboxane B2 (TXB2), 6-keto-prostaglandin (F1 alpha (6-keto-PGF1 alpha), and euglobulin clot lysis time (ECLT), were measured on each occasion. The ECG, heart rate and blood pressure were monitored during the exercise tests. After felodipine therapy there was a significant decrease in the plasma level of PF-4 and B-TG at rest. This effect was maintained during exercise. There was no significant change in platelet aggregation, ECLT, TXB2 or 6-keto-PGF1 alpha at rest or during exercise. Irrespective of therapy, the plasma levels of adrenaline and noradrenaline were increased and the ECLT was decreased when measured immediately after exercise. Thus, felodipine in modest therapeutic dosage decreases the plasma levels of B-TG and PF-4, indicating an inhibitory effect on platelet on release. The effect also occurred during exercise. Felodipine did not change fibrinolytic activity or the production of TXB2 or 6-keto-PGF1 alpha.

Adult↗