An unusual case of a primary blood collection tube with floating separator gel.

We describe an unusual case of a primary evacuated blood collection tube with floating separator gel, which has been collected from a 50-year-old man submitted to a percutaneous coronary intervention (PCI). The sample was collected from the femoral artery in a primary evacuated blood collection tube containing lithium-heparin. After centrifugation of the specimen, an unusual positioning of the separator gel was observed, which migrated at the topmost layer, whereas the packed blood cells remained in the middle and the plasma at the bottom. The potential interfering substance was found to be a contrast dye, 140 ml of which were administered to the patient during a revascularization procedure for acute myocardial infarction. The potential aspiration of the gel inappropriately positioned at the top of the tube by laboratory instrumentation can produce several technical and clinical problems, when not reliably detected. First, the needle of the instrument might be partially or completely obstructed by the gel, thus jeopardizing the integrity and correct functioning of the instrument. The aspiration of gel along with the sample matrix might also spuriously modify the test results, since an inappropriate amount of serum or plasma would be analyzed.