American Society for Clinical Pathology (ASCP) Histotechnician Certification Practice Exam

When performing a skin puncture, which specimen should be collected last?

1. EDTA microcollection tubes

2. Heparin microcollection tubes

3. Capillary blood gas tubes

4. Glucose testing microcollection tubes

The correct answer is: Heparin microcollection tubes

In the context of skin puncture procedures, the order of specimen collection is critical to prevent contamination and ensure accurate test results. Heparin microcollection tubes should be collected last due to the nature of the anticoagulant they contain. Heparin is used to prevent blood clotting and can interfere with the results of other tests if collected too early in the process. When collecting multiple specimens from a skin puncture site, it is essential to prioritize the tubes so that any potential contamination from anticoagulants is minimized. EDTA, which is also an anticoagulant, is drawn before heparin to avoid any interference in specific tests that may be affected by the presence of heparin. Capillary blood gas tests are typically performed first due to their sensitivity to contamination with other blood components. Glucose testing microcollection tubes similarly are collected prior to heparin to ensure that glucose results are not influenced by the heparin's anticoagulant properties. Thus, collecting the heparin microcollection tubes last is the best practice, ensuring that this specific anticoagulant does not interfere with the results of the other tests performed using the blood from the skin puncture.