Can laboratory tests be drawn from an intravenous (IV) line?

Drawing Labs from IV Lines: Clinical Guidance

Blood samples can be drawn from IV lines, but only under specific conditions with strict protocols to prevent contamination and ensure accuracy—arterial lines are preferred for critically ill patients, while peripheral venipuncture remains the gold standard when invasive monitoring is not clinically indicated.

Hierarchy of Blood Sampling Sites

For Critically Ill Patients with Invasive Monitoring

Arterial catheters should be the first-choice sampling site for all laboratory tests in patients whose illness severity justifies invasive vascular monitoring 1. If arterial access is unavailable, central venous catheters may serve as the second option, with meticulous attention to sterility and contamination prevention 1.

For Patients Without Invasive Monitoring

New peripheral venipuncture is strongly preferred over drawing from IV catheters 1. When possible, use 21-gauge needles for blood draws in adults 1.

Critical Safety Considerations

Contamination Risks

Blood sampling from a cannula lumen that carries infusion solutions other than sodium chloride 0.9% is NOT recommended 1. This prohibition exists because:

• IV catheters have significantly higher hemolysis rates compared to direct venipuncture 1
• Lubricant coatings and needle materials can contaminate specimens and interfere with immunoassays 1
• Infusion solutions can dilute or contaminate samples, producing dangerously misleading results 2, 3

Glucose Contamination Hazard

Glucose-containing infusions pose particular danger when drawing blood samples from IV lines 1, 4. Even minimal contamination can:

• Conceal true hypoglycemia, leading to delayed recognition and treatment 4, 5
• Produce falsely elevated glucose readings, triggering inappropriate insulin administration 4, 5
• Result in fatal neuroglycopenic brain injury within two hours 1, 5

Protocol When Drawing from IV Lines is Necessary

If Drawing from a Running IV Line

Drawing blood proximal (above) an infusing IV line results in significant dilutional effects and should be avoided 3. Research demonstrates that samples drawn above an infusing IV show deviation from baseline for most analytes 3.

If you must draw from the same arm as an IV infusion:

• Draw from below the IV insertion site, never above 3
• Alternatively, stop the infusion and wait a minimum of 3 minutes before drawing through the IV catheter 2
• For analytes present in the infused substance (especially glucose), wait longer than 3 minutes 2
• A 2-minute wait after stopping infusion shows acceptable results for most analytes except glucose and phosphorus 3

Preferred Alternative Approach

Always draw from the contralateral arm (opposite the IV site) as the first choice 2. This eliminates contamination risk entirely.

Arterial Line Sampling Protocol

Flush Solution Requirements

Only sodium chloride 0.9% (with or without heparin) should be used for arterial line flush solutions 1, 4. This prevents dangerous sampling contamination errors 4, 5.

Sampling Technique

Use closed arterial line sampling systems whenever possible to minimize contamination 1, 4. When using open systems:

• Minimize dead space volume between the sampling port and arterial lumen 4
• Use a readily distinguishable syringe for dead space removal versus the actual sample 1, 4
• Prevent flush solution from entering the dead space, sample, or three-way taps during the entire sampling process 1, 4

Quality Control Measures

Independently double-check the flush solution with a second practitioner before setup 4, 5. Additionally:

• Double-check the flush infusion bag at least once per nursing shift 4
• Recheck during all patient handovers 4
• Remove the bag from pressurizing devices during checks to verify contents 4

Verification of Unexpected Results

Any unexpectedly abnormal blood test or unusual variation from previous results should trigger immediate verification of the sampling source 1. Specifically:

• Check for possible sample contamination 1
• If contamination cannot be ruled out, draw a confirmatory sample from an alternative site 1
• For unexpectedly high glucose values from arterial lines, conduct a medical review before adjusting insulin therapy 1, 4

Common Pitfalls to Avoid

Never assume an IV catheter is equivalent to fresh venipuncture for laboratory accuracy 1. Key errors include:

• Drawing above a running IV infusion, which causes dilutional effects on most analytes 3
• Insufficient waiting time after stopping an infusion (minimum 3 minutes required) 2
• Using glucose-containing solutions anywhere in the system when glucose monitoring is needed 4, 5
• Failing to document variations from standard blood draw procedures 1

Documentation Requirements

Any deviation from standard venipuncture procedures must be carefully documented 1. This includes:

• The specific sampling site used
• Whether infusions were running or stopped
• Wait time after stopping infusions
• Type of catheter used (peripheral IV, central venous, arterial)