Hematological Tests

The shipment of biological specimens must comply with the protocols established by the courier or transport service used. In some cases, air transport requires compliance with the regulations of the International Air Transport Association (IATA) for hazardous materials.

Routine hematological tests require anticoagulated whole blood filled to the appropriate volume for the sample collection tube. Overfilling or underfilling the tubes can lead to unreliable analytical results due to an incorrect blood-to-additive ratio.

Ideally, several blood smears should be included. Blood smears should be prepared immediately after sample collection to minimize artifacts, including altered erythrocyte morphology, platelet clumping and general cell deterioration.

Anticoagulated blood should be kept refrigerated; blood smears should be stored at room temperature. EDTA is the anticoagulant of choice for mammalian complete blood counts.

EDTA is acceptable for most, but not all, non-mammalian species. The blood of rays, some bony fish and some species of reptiles and birds undergoes hemolysis when collected in EDTA, so heparin is usually used for these species.

Blood for coagulation tests should be collected in a citrate tube (with a blue cap) containing trisodium citrate (3.2% or 3.8%, as specified by the reference laboratory). It is imperative that the tube be filled to the appropriate volume, since underfilling can lead to falsely prolonged clotting times.

For plasma-based assays, citrated plasma should normally be separated from whole blood within 6 hours of collection to measure prothrombin time (PT) and activated partial thromboplastin time (aPTT). Plasma is separated by centrifugation at 1,500 g for 15 minutes, after which it is transferred to a secondary plastic tube without additives using a disposable plastic pipette.

Ideally, plasma should be analyzed within one hour of separation. However, many samples for coagulation tests are sent to reference laboratories for analysis, so compliance with the laboratory’s specific guidelines regarding sample storage is advised.

Freezing whole blood causes cell lysis and macroscopic hemolysis, which interfere with the tests; freezing of whole blood (during storage or transport of the sample) should be avoided.