The platelet function analyzer (PFA-100): an update on its clinical use

The platelet function analyzer, PFA-100, is a relatively new method which has been developed as a quantitative, simple and rapid in vitro tool of assessing primary hemostasis. The aim of this review is to summarize the published studies reporting on the utility of the PFA-100 device as a screening tool for primary hemostasis. Data were identified by searches of the published literature, including PubMed, references from reviews and abstracts from the most important meetings on this topic. The literature data document that the PFA-100 is a useful screening tool for the investigation of von Willebrand's disease and various acquired and congenital intrinsic platelet function disorders. It is also useful for evaluating primary hemostasis before surgical procedures and for monitoring desmopressin therapy in patients with type 1 von Willebrand's disease. Moreover, recent studies have shown its potential for therapeutic monitoring of the effectiveness of anti-platelet medications in cardiovascular disease management. Given its high sensitivity, speed and simplicity of use, we conclude that the PFA-100 could replace the in vivo bleeding time as a screening test for primary hemostasis in routine clinical practice.     

Effect of preanalytical time-delay on platelet function as measured by multiplate,PFA-100 and VerifyNow

Background and aims: Platelet function testing may help to identify poor responders to antiplatelet drugs. The aim of this study was to compare three commonly used platelet function tests with special focus on the pre-analytical influence of time-delay on the tested parameters.

Methods: We assessed ADP-induced platelet function by the Multiplate, Platelet Function Analyzer-100 (PFA-100) and VerifyNow in nine healthy volunteers and 36 patients receiving clopidogrel or prasugrel 1 and 3?hours after sampling. Results: The PFA-100 demonstrated non-closure time in 23 patients. A more graded response could be detected with the two other devices. Aggregation in whole blood (Multiplate) decreased after 3?hours compared to 1?hour in all subjects (p?p?Conclusion: Responses to ADP are time-dependent after blood sampling for the Multiplate in all subjects and for the VerifyNow in patients on antiplatelet drugs. For both devices, platelet aggregation was reduced 3?hours after sampling which may affect data interpretation and clinical consequences.     

Quality control of platelets during storage by the PFA-100: a comparison to platelet aggregation.

BACKGROUND AND OBJECTIVES: The PFA-100 examines platelet function by measuring closure time (CT) when whole blood is passing through a capillary and a filter membrane coated with a collagen/platelet agonist. Termination of the CT is achieved when adhered and aggregated platelets of the passing blood flow occlude the membrane. Two PFA-100 test cartridges are used to measure the CT of citrated whole blood; either the collagen/ADP (PCA) or the collagen/ epinephrine (PCE). We investigated the applicability of the PFA-100 test system for quality control of platelet concentrates in comparison with platelet aggregometry. MATERIALS AND METHODS: For platelet aggregation, the combination of ADP (100 microM/l) and collagen (20 microg/ml) were used as agonists (ADP/COL). In our test system, 25 microl epinephrine (10(-3) M) were added to the PCA cartridge (CT: PCAE) and 25 microl ADP (100 microM/l) to the PCE cartridge (CT: PCEA), respectively. Red blood cells from a blood group 0 donor were adjusted to a hematocrit of 43% using platelet rich plasma (8 x 10(5)/microl) of the respective platelet concentrate. Fourteen irradiated and non-irradiated platelet concentrates were examined on days 0, 3 and 5 after platelet preparation. Swirling without a scoring system and mean platelet volume (MPV) were also tested. Statistical analyses were performed by Pearson's range coefficient, the Mann and Whitney test, and the Wilcoxon test. RESULTS: Swirling was seen in all platelet concentrates. Mean platelet volume was normal during the whole observation period like the PCAE in non-irradiated products. Only the PCAE showed finite CTs during the whole storage time. Consequently, further testing was performed exclusively with the PCAE. Weak but significant correlations could be found between the PCAE and ADP/COL (r = -0.53 for non-irradiated platelet products, r = -0.62 for irradiated platelet products, p < or = 0.0001). Platelet function significantly decreased to around 60% of the initial value in the PCAE on day 5 of storage, ADP/COL decreased to 35% of maximum amplitude. A further decrease of approximately 10% was observed in the irradiated products, a fact which was significant in the PCAE. Only in the irradiated platelet products did MPV show a weak but significant correlation with the PCAE (r = 0.45, p = 0.002). CONCLUSION: Functional features of platelets from platelet concentrates characterized by ADP/COL induced aggregation can also be measured by the PFA-100. Yet, it has a higher sensitivity to platelet lesions induced by gamma-radiation. Further clinical studies will be necessary to determine whether PFA-measurements meet the quality criteria of MPV or swirling, or is superior in predicting in vivo viability. The relatively high cost of the test cartridge remains an obstacle for routine use.     

Control of aspirin effect in chronic cardiovascular patients using two whole blood platelet function assays. PFA-100 and Multiplate

In this study two aspirin sensitive platelet function tests which are based on the analysis of whole blood were evaluated and correlated with each other. In vitro bleeding time was determined using the PFA-100 analyzer (Dade Behring, Marburg, Germany) using the collagen/epinephrine cartridge and citrated blood. Whole blood aggregometry was performed using the Multiplate analyzer (Dynabyte medical, Munich, Germany) using hirudin blood (25 mug/ml). Aggregatin was triggered using arachidonic acid (ASPItest), collagen (COLtest) or TRAP-6 (thrombin receptor activating peptide, TRAPtest). Following informed consent citrated blood and hirudin blood was drawn from 76 cardiovascular patients which were on long-term aspirin therapy (aspirin patients). In addition hirudin blood was drawn from 57 healthy blood donors for assessment of whole blood aggregometry. PFA-100 closure times of the aspirin patients were 273 +/- 49 s. Based on the cut-off of 170 s a non response to the aspirin therapy was detected in 5 of 76 patients. Whole blood aggregation was comparable in the aspirin patients vs the blood donors AUC values in the TRAP test, whereas in COLtest and ASPItest significantly reduced aggregations were detected (p < 0.05). Of the five patients that had a normal PFA-100 closure time only one had normal aggregation in ASPItest, and also only one had a normal aggregation in COLtest. The high rate of response to the aspirin therapy which was found in PFA-100 and ASPItest can be explained by the assumed high level of compliance of the cohort. In the applied tests different patients were stratified as aspirin-non-responders. This highlights the importance of the assay conditions for the diagnosis of an aspirin-non-response.     

Pulmonary function testing: sources of error in measurement and interpretation

Valid pulmonary function data require that attention be paid to issues that can lead to errors in measurement or in interpretation. Routine procedures designed to reduce errors should be established. Among the most important of these are (1) assuring the accurate measurement and calculation of lung function parameters, which requires attention to accuracy when an instrument is brought into service in a laboratory and again when it is updated; (2) selecting reference equations and lower limits of normal appropriate for the patients being studied and for the equipment being used; (3) avoiding the errors introduced by using an excessive number of measurements in generating an interpretation; and (4) avoiding interpretation of results without considering the clinical setting and the pertinent elements of a complete data base.     

Impedance aggregometric analysis of platelet function of apheresis platelet concentrates as a function of storage time

Multiple electrode (impedance) aggregometry (MEA) allows reliable monitoring of platelet function in whole blood. The aims of the present study were to implement MEA for analyzing aggregation in platelet concentrates and to correlate results with storage time and blood gas analysis (BGA). We investigated the influence of platelet counts, calcium concentrations and agonists on platelet aggregation. Samples of apheresis concentrates up to an age of 12 days were investigated by MEA and BGA. For ASPI- and TRAPtest MEA was reproducible for a platelet count of 400 per 10^?9?L and a calcium concentration of 5?mmol L^?1. Platelets at the age of 2–4 days yielded steady aggregation. Platelet concentrates exceeding the storage time for transfusion showed steady aggregation up to 10 days, but a significant decline on day 12. Weak correlation was found regarding pCO₂ and MEA as well as regarding glucose concentration and MEA. Our results indicate that MEA is applicable for evaluation of aggregation in stored apheresis concentrates. Prolonged storage seems not to be prejudicial regarding platelet aggregation. Platelet concentrates showed acceptable BGA throughout storage time. Further studies are required to evaluate the application of MEA for quality controls in platelet concentrates.     

Iron-induced platelet aggregation measurement: a novel method to measure platelet function in stenting for ST segment elevation myocardial infarction

Background Iron and (stainless) steel are potent platelet aggregation activators, and may be involved in stent thrombosis, a serious complication after intracoronary stenting. Current platelet function tests are suboptimal, because of inappropriate agonists and/or lack of reproducibility. We tested the feasibility and reproducibility of a novel platelet function test using stainless steel as an agonist and compared it with other platelet function tests. Materials and methods In 111 patients with acute ST segment elevation myocardial infarction (STEMI), duplo measurements of iron (Fe)‐induced platelet aggregation (FIPA) were performed after clopidogrel, acetylsalicylic acid and/or tirofiban treatment. Within 1 h, citrated blood samples drawn from the femoral sheath before primary percutaneous coronary intervention were added to 100 mg of low carbon steel and after 5 s mixing with vortex, the samples were incubated for 15 min. The ratio between the non‐aggregated platelets in the agonist sample and platelets in a reference sample was calculated as the platelet aggregation inhibition. Results FIPA measurement was highly reproducible (correlation coefficient (R) = 0·942, P < 0·001 between duplo samples). FIPA correlated well with adenosine diphosphate‐induced platelet aggregation (R = 0·83, P < 0·001) but weakly with platelet function analyser‐100 bleeding time (R = 0·56, P < 0·001). FIPA could be measured in patients in which platelet aggregation could not be measured by platelet function analyser‐100 or after adenosine diphosphate. Conclusion This study showed good reproducibility of a novel platelet function test using stainless steel as an agonist and showed correlation with validated platelet function tests. We found that the novel platelet function test is a suitable test for measurement of platelet aggregation inhibition in patients undergoing stenting for STEMI, even when they are taking multiple antiplatelet regimens.