Blood collection tubes are evacuated glass or plastic vacutainers with color-coded rubber stoppers indicating additives for specific lab tests, drawn in "order of draw" (blood culture yellow, citrate blue, serum red/gold, heparin green, EDTA lavender, glucose gray) to avoid cross-contamination. Key types: EDTA lavender (CBC, hematology via chelation), sodium citrate light blue (PT/PTT coagulation 9:1 ratio), serum red/gold SST (chemistry after clotting, gel separation), lithium heparin green (plasma chemistry/ammonia), NaF gray (glucose preservation), SPS yellow (blood cultures). Invert 8-10x post-fill; process promptly to prevent hemolysis.