Heparinized venous blood gas syringes are associated with a significant decrease in measured packed cell volume in dogs due to hemodilution

Objective: To assess the effect of hemodilution on PCV when commercial preheparinized venous blood gas (PH-VBG) syringes are used compared to directly filled Hct tubes, and to evaluate the impact of delayed centrifugation on PCV.

Methods: A prospective study of 102 dogs presenting to a private emergency department between November 1, 2023, and February 29, 2024, with 306 corresponding blood samples. Samples were collected by direct venipuncture. Samples were analyzed with the use of 3 methods: directly filled microhematocrit tubes (direct), PH-VBG syringe (PH-VBG), and PH-VBG syringe with a 15-minute delay before centrifugation (delayed PH-VBG).

Results: Mean PCV of the direct method was 43.9%, the PH-VBG method was 41.7% (range, 11.0% to 60.0%; SD, 9.8%), and the delayed PH-VBG method was 40.1% (range, 7.0% to 60.0%; SD, 11.2%). When the direct and PH-VBG methods were compared, the direct method was biased on average 2.2% higher than the PH-VBG method, with limits of agreement (LOAs) of -0.9 to 5.3. The direct method was biased on average 3.8% higher than the delayed PH-VBG method, with LOAs of -4.3 to 11.9. In anemic dogs (n = 14), the direct method was biased on average 6.1% higher than the delayed PH-VBG method, with LOAs of -0.05 to 12.2. In nonanemic dogs (n = 88), the direct method was biased on average 2.3% higher than the PH-VBG method, with LOAs of -0.9 to 5.4.

Conclusions: Use of preheparinized syringes and delayed sample processing led to hemodilution and lower PCV values.

Clinical relevance: Direct venipuncture and immediate sample processing are recommended to ensure accurate PCV results.