Blood Sampling Guidelines for Clinical Practice
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, with central venous catheters as the second option if arterial access is unavailable, to prevent contamination and ensure accuracy 1
- For patients without invasive monitoring, new peripheral venipuncture is strongly preferred over drawing from IV catheters, with 21-gauge needles recommended for blood draws in adults 2, 3
Critical Safety Considerations
- Blood sampling from a cannula lumen that carries infusion solutions other than sodium chloride 0.9% is not recommended due to the risk of contamination and inaccurate results 4, 5, 6
- IV catheters have significantly higher hemolysis rates compared to direct venipuncture, and lubricant coatings and needle materials can contaminate specimens and interfere with immunoassays 2, 3
- Glucose-containing infusions pose a particular danger when drawing blood samples from IV lines, as even minimal contamination can conceal true hypoglycemia or produce falsely elevated glucose readings 4, 5, 6, 7
Protocol When Drawing from IV Lines is Necessary
- Only sodium chloride 0.9% (with or without heparin) should be used for arterial line flush solutions to prevent contamination and ensure accuracy 4, 5, 6, 7
- Closed arterial line sampling systems should be used whenever possible to minimize contamination, and open systems should be used with caution and strict protocols 4, 7
Quality Control Measures
- Independently double-check the flush solution with a second practitioner before setup, and double-check the flush infusion bag at least once per nursing shift and during all patient handovers 7, 8
- Remove the bag from pressurizing devices during checks to verify contents, and document any deviations from standard procedures 7
Verification of Unexpected Results
- Any unexpectedly abnormal blood test or unusual variation from previous results should trigger immediate verification of the sampling source, including checking for possible sample contamination and drawing a confirmatory sample from an alternative site if necessary 4
- For unexpectedly high glucose values from arterial lines, conduct a medical review before adjusting insulin therapy 4, 7
Common Pitfalls to Avoid
- Never assume an IV catheter is equivalent to fresh venipuncture for laboratory accuracy, and avoid drawing above a running IV infusion, using glucose-containing solutions, and failing to document variations from standard blood draw procedures 2, 3, 7, 8