Why is not drawing above the IV site ok? Understanding the Risks and Best Practices

October 12, 2025 •

4 min read

According to the World Health Organization, collecting blood samples from an existing peripheral venous access site can lead to false laboratory results due to hemolysis, contamination, and dilution by intravenous fluids. This is precisely why is not drawing above the IV site ok, as it creates a direct risk of mixing the infused solution with the blood specimen. Proper technique is critical for ensuring diagnostic accuracy and patient safety.

Quick Summary

Obtaining blood samples from above an active IV site risks contamination from infusing fluids and medications, which compromises laboratory test accuracy. The infused solutions can dilute the blood or alter analyte levels, potentially leading to misdiagnosis and inappropriate treatment. Alternative collection methods, such as using the opposite arm, are the standard of care to ensure reliable results.

Key Points

Risk of Sample Contamination: Drawing blood above an IV can contaminate the sample with infused fluids and medications, invalidating test results.
Potential for Misdiagnosis: Inaccurate lab results can lead to incorrect diagnoses and inappropriate treatment plans for the patient.
Hemodilution Affects Values: The mixing of IV fluids with blood artificially dilutes the sample, altering measured values like glucose and electrolytes.
Prioritize the Opposite Arm: The safest and most accurate method is to draw blood from the arm opposite the IV site.
Proper Technique is Crucial: If drawing from the same arm is necessary, collect blood distal (below) to the IV site only after pausing the infusion and discarding an initial blood volume.
Wait Time Required: Simply pausing the infusion is not sufficient; a wait time of at least two to three minutes is needed to allow residual fluid to equilibrate, especially for certain substances.
Proximal Draw as a Last Resort: Drawing blood from above the IV is highly discouraged and should only be done as a final option with extreme caution and extended wait times.

Understanding the Fundamental Risks

Drawing blood from a vein is a common and critical procedure in healthcare. However, when a patient has an active intravenous (IV) line, the standard approach must be altered to avoid compromising the sample. The primary reason for not drawing blood above or proximal to an IV site is the significant risk of sample contamination and dilution. An IV catheter infuses a constant flow of medication or fluid directly into the patient's bloodstream. The venous return carries this infused substance back towards the heart. A blood draw taken upstream from this point will capture not only the patient's blood but also a portion of the recently infused solution, resulting in an adulterated sample.

This contamination directly impacts the reliability of laboratory test results. For instance, if a patient is receiving a dextrose (sugar) solution, a blood draw from above the IV could yield an artificially high glucose reading. This false reading could lead a clinician to misinterpret the patient's metabolic state, potentially resulting in an incorrect diagnosis or treatment plan. The same principle applies to other infused substances, including electrolytes like calcium and potassium, or medications like heparin, which can alter coagulation test results.

The Science Behind Sample Dilution

When a blood specimen is collected too close to a running IV, the concentration of the infused fluid in the sample is higher than in the rest of the patient's bloodstream. This phenomenon is known as hemodilution. The degree of dilution can vary depending on several factors, including the rate of IV infusion, proximity of the draw site, and patient circulation. Even briefly stopping an IV might not prevent residual effects, especially for substances like dextrose. Clinical guidelines advise against drawing above an IV site unless absolutely necessary.

Potential Consequences of Incorrect Draws

Collecting a compromised blood sample can have significant clinical repercussions. Erroneous lab results can lead to a cascade of medical errors, such as incorrect dosage decisions, delayed treatment due to missed critical values, increased patient anxiety from repeat draws, unnecessary interventions, and wasted resources from rejected samples.

Comparing Different Phlebotomy Techniques Near an IV Site


Feature	Drawing Proximal (Above) IV Site	Drawing Distal (Below) IV Site	Drawing from Opposite Arm	Drawing from Central Line
Risk of Sample Dilution	Very High, especially with a running infusion.	Low, if IV is stopped and tourniquet is placed correctly.	Very Low, minimal risk unless patient circulation is poor.	Low, requires proper flushing and wasting of blood volume.
Risk of Sample Contamination	Very High, direct infusion mix.	Low, minimal risk if proper technique is used.	Very Low	Low, but higher than opposite arm draws if protocols aren't followed.
Diagnostic Accuracy	Poor, high likelihood of false results.	Good, if recommended wait times are observed.	Excellent, considered the gold standard.	Good, if strict flushing and wasting protocols are followed.
Recommended Use	Last Resort, requires extended wait time after stopping infusion.	Acceptable when opposite arm is unavailable.	First Choice, always preferred.	Primary option for difficult venous access.

Best Practices for Safe and Accurate Blood Sampling

When a patient has a peripheral IV, healthcare providers should follow a clear hierarchy of site selection. Adherence to established protocols is crucial.

Recommended steps for phlebotomy when a patient has a peripheral IV:

Prioritize the Opposite Arm: Always use the arm opposite the IV line first to eliminate contamination risk.
Use a Distal Site: If the opposite arm isn't available, draw from a site distal (below) the IV on the same arm. Turn off the infusion for at least two minutes and place a tourniquet between the IV and the draw site.
Draw and Discard: When drawing distal to the IV, discard 5-10 ml of blood to clear residual fluids before collecting the sample.
Use a Central Venous Catheter: For difficult access or frequent draws, a central line can be used with a specific flushing and wasting protocol.
Avoid Proximal Draws: Drawing from above the IV is strongly discouraged due to the high risk of contamination and difficulty ensuring complete washout, even with extended wait times. This is only a last resort under specific clinical judgment.

Conclusion

Drawing blood above an active peripheral IV is against standard guidelines and significantly risks inaccurate lab results due to dilution and contamination from infused substances. Such errors can lead to serious consequences, including misdiagnoses and inappropriate treatments. Healthcare providers must prioritize alternative sites, such as the opposite arm or a properly managed distal site, to maintain patient safety and ensure reliable diagnostic information. This adherence to proper phlebotomy technique is a core element of effective clinical care.

For more detailed clinical guidelines on blood collection from patients with vascular access, consult the ADLM website.

Frequently Asked Questions

Hemodilution is the process where intravenous fluids mix with the blood sample, artificially lowering the concentration of blood components. This happens when blood is drawn too close to an active IV site, making lab results appear different from the patient's true systemic values.

Yes, but not above the IV site. You can draw blood from a site distal (below) the IV catheter. The IV infusion should first be paused for at least two minutes, and a tourniquet must be placed between the IV and the draw site.

While pausing the IV is a necessary step, a one-minute wait is often insufficient, especially for analytes present in high concentrations in the infused fluid, like dextrose. Residual infused solution can still affect the local vein and contaminate the sample. A longer wait of two to three minutes is generally recommended, but some substances may require more time.

Tests measuring glucose, electrolytes (like potassium, calcium), and coagulation factors are highly susceptible to being altered by contamination from IV fluids. A draw above a dextrose infusion will produce a falsely high glucose level.

If contamination is suspected, a new blood specimen should be collected from the opposite arm, or a central line if available, following all guidelines. The original result should be documented as potentially inaccurate, and the new result should be prioritized for clinical decision-making.

Peripheral IV catheters have a small lumen, and the negative pressure required to draw blood can cause mechanical trauma to the red blood cells, leading to hemolysis (breakdown). Hemolyzed samples are typically rejected by the lab because they interfere with many test results.

For patients with IVs in both arms, the best option is often to use a central venous catheter (if present and per protocol) or to draw from a site distal to a paused IV infusion. If drawing distal, follow the procedure of pausing the infusion, applying a tourniquet below the IV, and discarding an initial blood volume.