Best Practices for Blood Sample Collection in Trap–Neuter–Return Programs: A Narrative Review of Critical Control Points for Free-Roaming Cats

Trap–neuter–return (TNR) programs are the leading non-lethal approach to managing free-roaming cat populations. When cats are anesthetized for surgical sterilization, veterinarians have a brief opportunity to obtain blood samples for pre-surgical screening, infectious-disease surveillance, and contribution to population-level reference-interval research. Field conditions, however, make collecting good-quality blood samples difficult: cats are often dehydrated and stressed, the procedure is kept brief, and their medical history is unknown. This narrative review draws on the American Society for Veterinary Clinical Pathology (ASVCP) reference-interval guidelines, feline anesthesia and the blood-collection literature, and operational experience from Portuguese TNR programs to describe seven points in the sampling workflow at which technique most often fails: anesthetic depth verification, controlled aspiration speed, immediate EDTA-tube mixing, post-venipuncture hemostasis, hemolysis recognition, precise FIV/FeLV point-of-care test timing, and adherence to a maximum-attempts limit. Three recurrent failure modes—collapsed veins from excessive aspiration, clotted EDTA samples from inadequate mixing, and hematoma formation from insufficient hemostasis—account for the majority of poor samples observed in routine practice. The framework presented here is intended to support reproducible, welfare-compliant sample collection during TNR operations, giving veterinary teams a single, structured reference that supports both animal welfare and the diagnostic value of the samples they collect.