Crime Scene Technician Practice Test 2026 – The All-in-One Guide to Exam Success!

Color-coded tubes tell you what preservative or additive is inside. A purple-cap tube contains EDTA, an anticoagulant that prevents blood from clotting and helps preserve DNA and other cellular material. That makes purple-capped tubes ideal for collecting blood standards, because you get non-clotted blood with intact DNA for accurate analysis. Other containers either don’t provide this specific preservative or aren’t suited to preserving DNA integrity—for example, dried blood spots on blot cards are a different format, and glass vials or plastic bags don’t inherently ensure the same level of preservation or standardization.