Research Output

Venous occlusion during blood collection decreases plasma nitrite but not nitrate concentration in humans

  Background: To maintain vascular tone and blood flow when tissue oxygenation is reduced, nitrite anions are reduced to nitric oxide (NO). From a practical perspective, it is unclear how the application of a tourniquet during blood collection might influence measurement of NO metabolites. Accordingly, this study evaluated the effect of venous occlusion on plasma nitrite and nitrate during venous blood collection. Methods: Fifteen healthy participants completed two trials that were preceded by the ingestion of nitrate-rich beetroot juice (BRJ; total of ~8.4 mmol nitrate) or no supplementation (control). In both trials, blood was collected using a venepuncture needle while a tourniquet was applied to the upper arm and using an indwelling intravenous cannula, from the opposing arm. The venepuncture samples were collected at 35 s post occlusion. Changes in the oxygenation of forearm flexor muscles were assessed using near-infrared spectroscopy. Plasma nitrite and nitrate were analysed using gas-phase chemiluminescence. Results: In the control trial, plasma nitrite was significantly elevated when collected via the cannula (179 ± 67 nM) compared to venepuncture (112 ± 51 nM, P = 0.03). The ingestion of BRJ increased plasma nitrite and values remained higher when sampled from the cannula (473 ± 164 nM) compared to venepuncture (387 ± 136 nM, P < 0.001). Plasma nitrate did not differ between collection methods in either trial (all P > 0.05). The delta changes in total-, deoxy-, and oxy-haemoglobin were all significantly greater during venepuncture sample compared to the cannula sample at the point of blood collection (all P < 0.05). Conclusions: Venous occlusion during venepuncture blood collection lowers plasma nitrite concentration, potentially due to localised changes in haemoglobin concentration and/or a suppression of endogenous NO synthesis. Accordingly, the method of blood collection to enable measurements of NO metabolites should be carefully considered and consistently reported by researchers.

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  • Date:

    11 June 2020

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  • Publisher

    Elsevier BV

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  • Funders:

    Historic Funder (pre-Worktribe)


Liddle, L., Burleigh, M. C., Monaghan, C., Muggeridge, D. J., & Easton, C. (2020). Venous occlusion during blood collection decreases plasma nitrite but not nitrate concentration in humans. Nitric Oxide: Biology and Chemistry, 102, 21-27.



Beetroot juice ,Cannula, Ischemia, Blood flow, Nitric oxide

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