Blood Specimen Collection Procedures

    

     Proper specimen collection presumes correct technique and accurate timing when necessary. Most hematology tests use liquid ethylenediaminetetraacetic acid (EDTA) as an anticoagulant. Tubes with anticoagulants should be gently but completely inverted end over end 7 to 10 times after collection. This action ensures complete mixing of anticoagulants with blood to prevent clot formation. Even slightly clotted blood invalidates the test, and the sample must be redrawn.

For plasma coagulator studies, such as prothrombin time (PT) and partial thromboplastin time (PTT), the tube must be allowed to fill to its capacity or an improper blood-to-anticoagulant ratio will invalidate coagulator results. Invert 7 to 10 times to prevent clotting.

Capillary Puncture (Skin Puncture)

Capillary blood is preferred for a peripheral blood smear and can also be used for other hematology studies. Adult capillary blood samples require a skin puncture, usually of the fingertip. For children, the tip of the finger is also often the choice. Infants younger than 1 year of age and neonates yield the best samples from the great toe or side of the heel.

Procedure

Capillary Blood

• Observe standard precautions (see Appendix A). Check for latex allergy. If allergy is present, do not use latex-containing products.
• Obtain capillary blood from fingertips or earlobes (adults) or from the great toe or heel (infants). Avoid using the lateral aspect of the heel where the plantar artery is located.
• Disinfect puncture site, dry the site, and puncture skin with sterile disposable lancet, perpendicular to the lines of the patient's fingers, no deeper than 2 mm. If povidone-iodine is used, allow to dry thoroughly.
• Wipe away the initial drop of blood. Collect subsequent drops in a microtube or prepare a smear directly from a drop of blood.
• After collection, apply a small amount of pressure briefly to the puncture site to prevent painful extravasation of blood into the subcutaneous tissues.
   Dried Blood Spot
  • In this method, a lancet is used, and the resulting droplets of blood are collected by blotting them with filter paper directly.
  • Check the stability of equipment and integrity of supplies when doing a finger stick. If provided, check the humidity indicator patch on the filter paper card. If the humidity circle is pink, do not use this filter paper card. The humidity indicator must be blue to ensure specimen integrity.
  • After wiping the first drop of blood on the gauze pad, fill and saturate each of the circles in numerical order by blotting the blood droplet with the filter paper. Do not touch the  
  • patient's skin to the filter paper; only the blood droplet should come in contact with the filter pape.
  • If an adult has a cold hand, run warm water over it for approximately 3 minutes. The best flow occurs when the arm is held downward, with the hand below heart level, making effective use of gravity. If there is a problem with proper blood flow, milk the finger with gentle pressure to stimulate blood flow or attempt a second finger stick; do not attempt more than two.
  • When the blood circles penetrate through to the other side of the filter paper, the circles are fully saturated.
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