Final answer:
During a capillary puncture, the first blood collected should be for tests that require either plasma or serum without tissue fluid or clotting factor interference. Tubes containing anticoagulants such as EDTA or lithium heparin are used to prevent clotting and facilitate plasma separation.
Step-by-step explanation:
When performing a capillary puncture to collect blood, the first thing you should collect is any blood necessary for tests that could be affected by tissue fluid contamination or clotting. In a medical setting, one of the first tubes typically collected contains anticoagulants, such as EDTA or lithium heparin, that prevent the blood from clotting and prepare it for plasma separation by centrifugation.
For plasma-based assays, the blood collected into anticoagulant tubes like EDTA is subsequently centrifuged to obtain the plasma needed for these tests. In the case where serum is required, such as for certain serology tests or biochemical analyses, the blood would be collected into a serum separator tube and allowed to clot before centrifugation, thus avoiding activation of clotting factors which would otherwise remain in plasma.
Understanding the proper collection and processing of blood samples is a critical aspect of phlebotomy and medical lab technology practices to ensure accurate diagnostic results and appropriate patient care.