Blood collection techniques, heparin and quinidine protein binding

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Abstract
With the use of glass syringes without heparin and all glass equipment, the percent of unbound quinidine was measured by ultrafiltration and a double-extraction assay method after addition of 2 µg/ml of quinidine sulfate. Compared to the all-glass method, collection of blood using Vacutainers resulted in an erroneous and variable decrease in quinidine binding related to blood to rubber-stopper contact. With glass, the unbound quinidine fraction was (mean ± standard error) 10 ± 1% in 10 normal volunteers, 8.5 ± 1.5% in 10 patients with congestive heart failure, and 11 ± 2% in 11 patients with chronic renal failure (although in 8 of the latter 11 patients the percent of unbound quinidine was 4 or more standard errors from the mean of the normal group). During cardiac catheterization, patients had markedly elevated unbound quinidine fractions: 24 ± 2% (p < 0.001). This abnormality coincided with the addition of heparin in vivo and was less apparent after the addition of up to 10 U/ml of heparin in vitro (120% and 29% increase in unbound quinidine fractions, respectively). Quinidine binding should be measured with all glass or equivalent equipment.