Medical Assistant NCMA Practice Test

Answer: D - All of the choices may cause false negative blood culture results. Not filling the container completely may produce a false negative result because the organisms present in the blood may be at levels undetectable unless the proper amount is collected. Injecting air into the anaerobic container will kill anaerobic organisms, resulting in a false negative result. Tincture of iodine is an antiseptic, used to create an aseptic puncture site. Some facilities may require iodine painting of the rubber stoppers in the collection tubes. Allowing the iodine to dry completely on the skin and/or stopper, as well as taking care not to over-paint the stopper, will avoid iodine-contamination of the blood sample. Introduction of iodine into the blood sample may kill the organisms present, producing a false negative.