9.6 IV Contamination & Analytical Interference

9.6 IV Contamination & Analytical Interference

Specimen Collection in Patients with Intravenous (IV) Lines

Collecting diagnostic blood samples from an extremity containing an active intravenous (IV) infusion catheter is a major clinical challenge. Drawing proximal to (above) or directly through an active IV line contaminates the specimen with infusing crystalloids, colloids, or medications, producing extreme, life-threatening laboratory artifacts:

• Dextrose 5% in Water ($D_5W$): Infusing glucose produces massive false hyperglycemia (blood glucose values exceeding 1,000 mg/dL).
• Normal Saline (0.9% NaCl): Causes profound false hypernatremia and hyperchloremia while diluting potassium, bicarbonate, and hematocrit.
• Heparin Flushes / Infusions: Completely destroys the validity of Prothrombin Time (PT/INR), activated Partial Thromboplastin Time (aPTT), and fibrinogen assays.
• Potassium Additives (e.g., KCl in IV bags): Causes lethal pseudohyperkalemic values.

                 MANDATORY CLSI 7-STEP PROTOCOL FOR IV DRAWS
  ┌────────────────────────────────────────────────────────────────────────┐
  │ STEP 1: PRIORITIZE THE NON-IV ARM                                      │
  │ • Always select the opposite, non-IV arm whenever accessible.          │
  ├────────────────────────────────────────────────────────────────────────┤
  │ STEP 2: SELECT A SITE DISTAL (BELOW) THE IV CATHETER                   │
  │ • If the IV arm is unavoidable, choose a vein DISTAL to the IV site.   │
  │ • STRICT PROHIBITION: Never draw proximal to (above) an active IV.     │
  ├────────────────────────────────────────────────────────────────────────┤
  │ STEP 3: NURSE-DIRECTED 2-MINUTE IV SHUTOFF                             │
  │ • Request a qualified nurse to turn off the IV infusion for at least   │
  │   TWO FULL MINUTES (CLSI standard) prior to performing venipuncture.   │
  │ • Phlebotomists must NEVER adjust or turn off IV pumps independently.  │
  ├────────────────────────────────────────────────────────────────────────┤
  │ STEP 4: APPLY TOURNIQUET DISTAL TO IV SITE                             │
  │ • Position the tourniquet below the IV cannula, between the IV site    │
  │   and the selected venipuncture puncture point.                        │
  ├────────────────────────────────────────────────────────────────────────┤
  │ STEP 5: COLLECT AND DISCARD A 5 mL DISCARD TUBE                        │
  │ • Draw and discard a minimum 5 mL discard tube (or 2x line dead space) │
  │   before collecting diagnostic tubes to clear residual IV fluid.       │
  ├────────────────────────────────────────────────────────────────────────┤
  │ STEP 6: DOCUMENT COLLECTION DETAILS ON REQUISITION                     │
  │ • Document on the requisition that blood was collected distal to an IV,│
  │   note the 2-minute stoppage, and record the specific IV solution.     │
  ├────────────────────────────────────────────────────────────────────────┤
  │ STEP 7: PROMPT NURSE NOTIFICATION TO RESTART IV                        │
  │ • Immediately inform the nurse that the draw is completed so the IV   │
  │   infusion can be safely restarted without clinical delay.             │
  └────────────────────────────────────────────────────────────────────────┘

  INCORRECT (PROXIMAL / ABOVE IV):          CORRECT (DISTAL / BELOW IV):
  ================================          ===========================
  [Shoulder]                                [Shoulder]
      |                                         |
  [Puncture Site] <-- WRONG! Contaminated!      |
      |                                     [IV Catheter Site] (Turned off 2 min)
  [IV Catheter Site] (Infusing fluid)           |
      |                                     [Tourniquet]
      |                                         |
  [Hand]                                    [Puncture Site] <-- CORRECT! (5 mL Discard)
                                                |
                                            [Hand]

Recognizing Contamination in the Result

The Detailed Test Plan asks the technician to "prevent interference in clinical analysis of blood constituents (e.g., alcohol, IV fluids, edema)." The exam usually presents a result pattern and asks you to name the cause.

[!IMPORTANT] The tell-tale sign of IV contamination is internal inconsistency. A glucose of 800 mg/dL alongside a sodium of 118 mmol/L and a potassium of 1.9 mmol/L in a patient who looks well is not a metabolic crisis; it is a dextrose drip drawn through. Recognizing the pattern and recollecting correctly is what prevents a dangerous insulin order.

The Protocol for Drawing on a Patient with an IV

1. Use the opposite arm. This is always the first choice and resolves the problem entirely.
2. If both arms have IVs, use a hand vein below the IV site on one arm, or ask nursing whether one line can be paused.
3. If a draw below an active IV is unavoidable, the accepted protocol is: have the infusion stopped for at least 2 minutes, apply the tourniquet below the IV site, puncture distal to (below) the IV, discard the first 5 mL of blood, then collect the specimens.
4. Document it. Note that the specimen was drawn below an IV, which line was involved, and what was infusing, so the laboratory and the provider can interpret the result.

[!WARNING] A phlebotomist does not stop, restart, disconnect, or manipulate an IV line. Only licensed nursing or provider staff may do so. Your role is to request the pause and wait for confirmation.

Central Lines, Ports, and Dialysis Access

Blood drawn from central venous catheters, implanted ports, and PICC lines is generally outside the phlebotomy scope of practice and is performed by specially trained nursing staff. An arteriovenous fistula or graft used for hemodialysis is absolutely off limits for venipuncture: puncturing it risks thrombosis, infection, and loss of a surgically created access the patient depends on for survival. Draw from the non-access arm, and if the patient has access in both arms, consult nursing before proceeding.