What are the requirements for drawing blood for the anti-tissue transglutaminase (tTG) Immunoglobulin A (IgA) test?

Requirements for Drawing Blood for Anti-Tissue Transglutaminase (tTG) IgA Test

Blood for anti-tTG IgA testing should be collected via direct venipuncture into a standard plastic tube containing 0.109 M sodium citrate as the anticoagulant, with proper sample handling to avoid hemolysis which can significantly affect results.

Blood Collection Procedure

• Use a straight needle rather than a butterfly needle for venipuncture to minimize contact activation and hemolysis 1
• If a butterfly needle must be used, use short connecting tubes to reduce the risk of hemolysis 1
• Apply tourniquet only long enough to locate the vein (ideally 60 seconds or less) to prevent blood cell activation and hemolysis 1
• Discard the first tube of blood (or at least the first few milliliters in pediatric patients) 1
• Draw blood directly into the collection tube rather than using a syringe first to prevent activation of coagulation 1
• Use plastic collection tubes rather than glass tubes to avoid contact activation 1
• Ensure proper filling of the tube (neither under nor overfilled) for accurate results 1

Sample Handling and Processing

• Keep blood samples at room temperature after collection 1
• Process samples as soon as possible, preferably within 1 hour of collection 1
• Avoid using pneumatic tube transport systems as they can modify test parameters 1
• Use hand-carrier transport to deliver samples to the laboratory 1
• Ensure the patient is on a gluten-containing diet when testing for celiac disease to avoid false negative results 2, 3

Important Considerations

• Hemolysis can significantly affect anti-tTG IgA test results, even when hemolysis is not visibly apparent 4
• Hemolysis index (HI) ≥25 can yield inconclusive anti-tTG IgA results as TTG is abundant in erythrocytes and released upon hemolysis 4
• Document any pre-analytical conditions that may potentially influence test results 1
• Consider measuring total IgA levels along with anti-tTG IgA to rule out IgA deficiency which could affect interpretation 2, 5

Storage Requirements

• If testing cannot be performed immediately, freeze plasma samples as soon as possible 1
• For long-term storage, maintain samples at -80°C where coagulation proteins remain stable for at least 2 years 1
• When using frozen samples, thaw at 37°C before testing 1
• Avoid using samples that have been freeze-thawed more than once 1

Common Pitfalls to Avoid

• Prolonged tourniquet application can lead to blood cell activation and affect test results 1
• Drawing blood from catheters, especially those containing heparin, can contaminate the sample 1
• Hemolyzed samples can yield falsely decreased anti-tTG IgA values due to released TTG interfering with antibody binding 4
• Testing while the patient is on a gluten-free diet can lead to false negative results 2, 3