Stat Potassium and CBC With a Left Mastectomy and Right IV
At 11:05 in an oncology infusion center, a 62-year-old woman needs STAT potassium, CBC, and PT/INR. Her left arm has a modified radical mastectomy with lymphedema. Her right forearm has a 20-gauge IV in the cephalic vein infusing 0.9% saline at 75 mL/hr. The right antecubital vein is palpable but sits 3 cm above the IV site. Her right hand veins are small and scarred from prior chemotherapy sticks. The provider is in surgery and unavailable for 30 minutes. The infusion nurse says, 'Just draw above the IV; it is fine.' The patient is anxious and asks whether the draw can wait until the IV is removed. The order is marked STAT, and the potassium result will be used to decide whether to hold digoxin. The lab uses a butterfly collection set with a 3 mL discard tube available.
1. Which venipuncture site is acceptable, and which sites must be avoided? Explain.
Read the worked answer
Avoid the left arm because of mastectomy and lymphedema; that arm is at increased risk for infection and poor lymphatic drainage. Avoid the right antecubital vein above the IV because blood drawn proximal to an infusing IV can be diluted and contaminated with IV fluid. The most acceptable site is the right hand distal to the IV, using a warm pack and careful technique, if a vein can be accessed. Because the hand veins are scarred, do not repeatedly probe. If no safe site is available, escalate to the provider or a rapid-response/ vascular-access resource; do not use the foot without an order. The nurse's instruction to draw above the IV is not acceptable for a STAT potassium that will guide digoxin dosing.
2. What order of draw should be used if blood is obtained from the right hand with a butterfly and a 3 mL discard tube?
Read the worked answer
Use the discard tube first to prime the butterfly tubing and reduce tissue-fluid contamination. Then draw in this order:
- Light blue for PT/INR; fill to the required line.
- Gold/red serum tube for potassium and chemistry.
- Lavender EDTA for CBC. If the potassium order is being collected in a green lithium heparin tube instead of serum, place the green tube after the gold and before the lavender. The key reasoning is that coagulation tubes are most affected by incomplete filling and order-of-draw errors, so they come before additive tubes when no blood culture is ordered.
3. How should the technician respond to the nurse's instruction to 'just draw above the IV'?
Read the worked answer
Respectfully decline and explain the specific risk: blood drawn above a running IV can be diluted by saline, causing a falsely low potassium, and can alter other results. State that the potassium is being used to decide whether to hold digoxin, so accuracy is critical. Offer the safe alternative: draw from the hand distal to the IV or escalate for another site. Notify the provider or charge nurse about the delay and document the nurse's request, the refusal, and the action taken. The judgment is to protect specimen integrity and patient safety rather than comply with an unsafe shortcut.