A Remote Assay for Measuring Canine Platelet Activation and the Inhibitory Effects of Antiplatelet Agents

Validation of PAMFix, A Novel Platelet Stabilization Product, for Use on Flow Cytometric Analysis of Pigtailed Macaque (Macaca nemestrina) Blood

Quantification of platelet activation can be important for patients suffering from prothrombotic states, bleeding diatheses, cardiovascular disease, and other diseases in which platelets play a role. The analysis of platelet activation ex vivo typically requires blood processing immediately after venipuncture; this requirement can create problematic situations for both medical and research personnel. Flow cytometry is one method used to quantify platelet activation by measuring the expression of platelet surface markers with fluorescent antibodies. PAMFix is a fixative that stabilizes platelet activation markers, including P-selectin (CD62P), in whole blood. PAMFix has already been validated for use in humans and canines for stabilization of whole blood, thus allowing flow cytometry to be performed up to 28 and 22 d, respectively, after venipuncture and reducing the need for expensive equipment and highly trained personnel at the location of venipuncture. Pigtailed macaques (Macaca nemestrina) are frequently used in infectious disease research that may require containment conditions that preclude immediate processing of samples. In this study, we tested the efficacy of PAMFix on whole blood from pigtailed macaques to determine the short- and long-term effects of PAMFix on platelet P-selectin expression as analyzed by flow cytometry.

Extended sample storage for platelet function testing in healthy dogs

BACKGROUND

Platelet function testing is important for monitoring the effects of antiplatelet therapy but is not readily used due to time constraints for testing and the need for specialized equipment.

OBJECTIVES

This study evaluated the effects of various storage methods on selected platelet function tests to determine if delayed platelet function testing is feasible in canine blood samples. Our hypotheses were that platelet function would not decline during storage and, thus, no differences in test results would be found over time.

METHODS

Thirteen healthy dogs were studied. Citrated blood samples were tested with a Platelet Function Analyzer-200 (PFA), which mimics high-shear conditions, using P2Y and CADP cartridges, after being held at room temperature for 2 h and refrigerated for 24 and 48 h. Plateletworks (PW), which measures aggregation based on platelet counting, was performed on an optical hematology analyzer using 10-min-old native samples, citrated samples held at room temperature for 3-4 h and refrigerated for 24 and 48 h, and samples stored in the preservative solution, AGGFix, up to 7 days.

RESULTS

PFA closure times increased with storage, especially with the P2Y cartridge. Median aggregation with fresh PW was 94%, and this was maintained at all time points (range of median values 88%-94%). Most samples showed decreased, yet still robust (>70%), aggregation with longer storage. Spontaneous aggregation in citrate was noted in most dogs. AGGFix stabilized platelet aggregates to allow for delayed testing.

CONCLUSIONS

Delayed platelet function testing is feasible, but ranges of expected values may differ from tests using fresh samples.

Validation of Plateletworks ADP for the ProCyte Dx analyzer

BACKGROUND

Platelet function testing in cats allows determination of clopidogrel effect. Plateletworks assesses aggregation based on decreasing platelet counts on hematology analyzers in response to agonists. It has not been validated for the IDEXX ProCyte Dx analyzer. Ideal time to perform analysis and the utility of other platelet parameters have not been fully assessed.

OBJECTIVES

To validate Plateletworks ADP on the ProCyte Dx, to investigate the utility of various platelet parameters using Plateletworks ADP, and determine the ideal time to perform analysis.

ANIMALS

Twenty healthy cats recruited from the general population used for transference of reference intervals to a new analyzer, and 10 cats receiving clopidogrel to determine clopidogrel effect.

METHODS

Plateletworks ADP using the ProCyte Dx and ADVIA 2120i analyzer was run simultaneously in both healthy cats and cats receiving clopidogrel, and CBC results at different timepoints were compared between analyzers.

RESULTS

Aggregation was significantly different (P < .001) between analyzers. Cohen's kappa showed almost perfect agreement for determination of clopidogrel effect, and the area under the curve of the receiver operating characteristic was 1.0. Lower limits of the aggregation reference interval in healthy cats were 28.8% on the ProCyte Dx and 12.5% on the ADVIA 2120i. Coefficients of variation for platelet parameters were not different between analyzers. No significant changes in mean platelet volume, plateletcrit, large platelets, and mean platelet component were identified. No significant change in aggregation was observed within the first hour after phlebotomy.

CONCLUSIONS AND CLINICAL IMPORTANCE

Our study validated the Plateletworks ADP system on the ProCyte Dx analyzer. Samples may be analyzed up to 1 h after collection.

Abnormal platelet activity in dogs and cats - impact and measurement

Abnormal platelet activity can either lead to bleeding tendencies or inappropriate thrombus formation and can occur secondarily to a wide variety of disease processes, with a range of clinical consequences and severity. This article will discuss the pathophysiology of platelet function abnormalities and consider a logical diagnostic approach applicable to veterinary practice. Recent advances in platelet function testing will then be discussed, with regards to detection of platelet dysfunction and tailoring of pharmacological manipulation. Although many of these tests are still confined to research or academic institutions, techniques for indirectly assessing platelet function are starting to become more widely available. Although we still require further research to develop guidelines for the use of these tests in clinical decision-making, the recent advances in this field are an exciting step forward in being able to detect and manage platelet dysfunction in both primary care and referral practice.