What effect would collecting blood above an intravenous (IV) site have on hemoglobin (Hgb) and hematocrit (Hct) levels during a blood cell transfusion?

Effect of Blood Collection Above an IV Site During Blood Cell Transfusion

Collecting blood above an intravenous (IV) site during transfusion of blood cells would result in falsely higher hemoglobin (Hgb) and hematocrit (Hct) values (answer C is correct). This occurs because the sample would be contaminated with the transfusing blood cells, leading to artificially elevated measurements that do not accurately reflect the patient's true circulating values.

Mechanism of Falsely Elevated Results

When blood is drawn proximal to (above) an IV site where blood products are being transfused, the following occurs:

• The blood sample becomes contaminated with the transfused red blood cells that are being infused
• This contamination artificially increases the concentration of red blood cells in the sample
• The result is falsely elevated hemoglobin and hematocrit values that do not represent the patient's actual circulating levels

Evidence-Based Recommendations

The American Association of Blood Banks and other guidelines emphasize the importance of proper blood sampling techniques during transfusion 1:

• Blood samples should ideally be drawn from the contralateral arm (opposite to the transfusion site)
• If blood must be drawn from the same arm as the transfusion, it should be collected below the IV site, never above it
• When drawing blood proximal to an IV site (even when the infusion is temporarily stopped), a waiting period is necessary to avoid contamination

Research has demonstrated that when blood must be drawn proximal to an IV line, significant differences in analyte values can occur 2:

• Even after shutting off an infusion, wide ranges in differences persist for many analytes
• A minimum three-minute interval is recommended when drawing blood proximal to a shut-off infusion
• For substances present in the infused solution, longer intervals may be advisable

Clinical Implications During Blood Transfusion

During blood cell transfusion, the implications of drawing blood above the IV site are particularly significant:

• Hemoglobin and hematocrit measurements are critical for assessing the effectiveness of transfusion therapy
• Falsely elevated results could lead to premature termination of necessary transfusions
• Clinical decisions based on these inaccurate values could compromise patient care

The AAGBI guidelines emphasize that hemoglobin concentration should be measured before and after every unit of RBC transfused in non-bleeding patients 3. Using falsely elevated values would undermine this monitoring process.

Proper Blood Sampling During Transfusion

To obtain accurate hemoglobin and hematocrit values during transfusion:

• Draw blood from the opposite arm whenever possible
• If using the same arm, collect from a site distal to (below) the transfusion
• Temporarily stop the transfusion if blood must be collected proximal to the site
• Wait at least 3-5 minutes after stopping the infusion before collecting the sample
• Resume transfusion only after sample collection is complete

Common Pitfalls to Avoid

• Failing to recognize that transfused blood will contaminate samples drawn above the IV site
• Assuming that briefly stopping the transfusion eliminates the risk of contamination
• Basing clinical decisions on falsely elevated hemoglobin/hematocrit values
• Not allowing adequate circulation time after stopping an infusion before drawing blood

Remember that accurate hemoglobin and hematocrit measurements are essential for proper transfusion management, as guidelines recommend transfusing to specific hemoglobin targets (typically 7-8 g/dL for most patients) 1, 4.