I85PREP
⌘ K
CI-CPT study materials
CI-CPT study resources

CI-CPT: Blood Collection

CI-CPT · Work through your exam, one topic at a time.

All guide sections

Blood Collection

Blood Collection

The Blood Collection domain tests the candidate's ability to perform venipuncture and capillary collection safely and accurately. Questions focus on site selection, equipment choice, order of draw, tube additives, and immediate complication management.

Core rules

  • Identify the patient with two independent identifiers; label tubes at the bedside after collection.
  • Apply the tourniquet 3-4 inches above the site for no more than 1 minute; release it once blood flow begins and before needle withdrawal.
  • Choose the median cubital vein first, then cephalic, then basilic; avoid the basilic area in patients at risk of arterial puncture.
  • Cleanse with 70% isopropyl alcohol in concentric circles and allow it to dry fully; do not fan or blow on the site.
  • Use a 21-gauge needle for a healthy median cubital vein, 23-gauge for small or fragile veins, and 20-gauge for large veins or rapid fill.
  • Follow the CLSI order of draw: blood culture, light blue (sodium citrate), red/gold (serum), green (heparin), lavender (EDTA), gray (fluoride/oxalate).
  • Invert additive tubes gently the required number of times; never shake, because shaking causes hemolysis.

Worked example

A provider orders a blood culture, PT/INR, a metabolic panel, a CBC, and a glucose test. The correct draw order is blood culture, light blue, gold, lavender, gray. The culture goes first to reduce contamination risk. The light blue tube is next because citrate must not receive EDTA or heparin, which alter coagulation results. The gold serum tube follows before heparin and EDTA. Lavender precedes gray because EDTA can interfere with fluoride/oxalate glucose testing in some assays, and the gray tube is last. Each tube is filled completely; a short-draw citrate tube changes the blood-to-additive ratio and invalidates the INR.

Traps

  • Drawing the citrate tube after EDTA: even trace EDTA carryover binds calcium and falsely prolongs clotting times.
  • Underfilling the light blue tube: the most common cause of rejected coagulation specimens.
  • Using a 23-gauge needle on a large vein with a slow draw: increases hemolysis and falsely raises potassium.
  • Palpating the site after cleansing: recontaminates the puncture area.
  • Leaving the tourniquet on during the entire draw: hemoconcentration raises potassium and protein.