Sterile, leak-proof tubes made of clear, unbreakable disposable plastic Pre-defined vacuum for exact draw volumes Use tubes with round bottoms for chemical analyses; conical bottom tubes for microscopic examination of urine sediment Use tubes with boric acid preservative for specimens tested for an otherwise unstable analyte or specimens for microbiological studies (stable up to 24 hours) Tubes with preservatives should be inverted 6-8 times following collection in order to achieve homogenous mixing