Platelet function testing is important in certain veterinary diseases and is also important for monitoring effects of anti-platelet medications such as clopidogrel. However, platelet function testing is not readily available or utilized because of time-constraints for testing and the need for specialized equipment. This study aimed to test various sample storage methods to allow for delayed platelet function testing in healthy and ill dogs. This study evaluated the use of citrate, refrigeration, and time on two platelet function tests, Plateletworks® (PW) and INNOVANCE® Platelet Function Analyzer-200 (PFA-200) (P2Y and CADP cartridges), in healthy and ill dogs. It also evaluated AGGFix solution to stabilize platelet aggregates formed with PW, and measure aggregation at various time-points using an optical hematology analyzer in both populations of dogs. Spontaneous aggregation in citrate was also evaluated. In ill dogs, the effect of these storage methods on clopidogrel monitoring was further assessed. In healthy dogs, the use of same-day citrated whole blood with PW yielded results similar to fresh 10-minute PW. Most samples showed decreased, yet still robust aggregation in most cases, with prolonged storage. Spontaneous aggregation in citrate was noted in almost all dogs. AGGFix stabilized platelet aggregates to allow for 24-hour testing. As with citrate, robust aggregation was maintained at all measurement time-points. PFA-200 closure times increased with prolonged storage; this was more pronounced with the P2Y cartridge than with the CADP cartridge. In ill dogs, the use of citrated whole blood with PW led to an increase in aggregation in most dogs; all dogs receiving clopidogrel at the time of testing showed an increase in aggregation compared to native 10-minute PW. Spontaneous aggregation in citrate was also noted in all ill dogs. AGGFix was successful at stabilizing platelet aggregates in all dogs; however, robust aggregation was noted in dogs receiving clopidogrel despite a native PW test result showing appropriate clopidogrel effect. PFA-200 closure times were, as in healthy dogs, prolonged with storage. This result was more pronounced with the P2Y cartridge than with the CADP cartridge. Delayed platelet function testing is feasible, but ranges of expected values may differ from native tests.