Serum Biochemical Analysis 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.

Anticoagulants present in plasma can lead to an increase or decrease in the values of the test analytes (for example, samples contaminated with potassium-EDTA have artificially elevated potassium concentrations and decreased calcium concentrations); therefore, by default, serum should be submitted.

However, in some cases, heparinized plasma may be acceptable or possibly necessary. It is recommended to consult the laboratory before collecting the sample for any non-routine test or species.

Because lipemia can interfere with a number of chemical tests for dogs and cats, withholding food for 12 hours before sample collection is advised, unless there is a potential medical contraindication, such as in pediatric patients or toy dog breeds.

For serum samples, blood should be drawn into a serum tube (red top) or a serum separator tube (tiger top). The sample should be kept at room temperature for 20-30 minutes to allow complete clot formation and retraction. Incomplete clot formation can cause the serum to gel due to latent fibrin formation.

The clot should be separated from the glass by gently rimming the walls of the tube with an applicator stick to loosen the clot. The sample should then be centrifuged at moderate speed (~450 rpm) for 10 minutes.

If the sample has been collected in a serum separator tube, centrifugation will deposit a layer of polymeric gel between the packed cells and the serum. The gel layer should be inspected to ensure the integrity of the barrier, and repeating the centrifugation is recommended if there is a visible crack in this layer.

If a serum tube (red-top) has been used, the serum should be removed and transferred to a clean tube to minimize artifacts (e.g., glycolysis in the cellular component of the blood sample can lead to an artificial decrease in glucose concentration). The serum should be refrigerated or frozen until analysis. Delays in analysis can adversely affect the results of several analytes.

Rough handling of the sample or incomplete separation of erythrocytes from the serum can promote hemolysis, which can interfere with certain tests. For chemistry panels, 0.5 mL of serum is usually preferred, although the laboratory’s minimum requirements may vary and should be consulted for serum volumes < 0.5 mL.