Capillary Puncture

• A lancet is a sterile, disposable, sharp-pointed or bladed instrument that either punctures or makes an incision in the skin to obtain capillary blood specimens for testing.
• Microcollection containers, also called microtubes, are special small plastic tubes used to collect the tiny amounts of blood obtained from capillary punctures.
• Microhematocrit tubes are disposable, narrow-bore plastic, or plastic-clad glass capillary tubes that fill by capillary action and typically hold 50 to 75 μL of blood.
• Microhematocrit tubes are used primarily for manual hematocrit (Hct), also called packed cell volume determinations.
• The tubes come coated with ammonium heparin, for collecting Hct tubes directly from a capillary puncture, or plain, to be used when an Hct tube is filled with blood from a lavender-top tube.
• Heparin tubes typically have a red or green band on one end; nonadditive tubes have a blue band.
• Smaller microhematocrit tubes designed for use with special microcentrifuges require as little as 9 μL of blood and are often used in infant and child anemia screening programs and pediatric clinics.
• Plastic, clay, or wax-type sealants that come in small trays are used to seal one end of microhematocrit tubes.
• CBG collection tubes are long thin narrow-bore capillary tubes. They are normally plastic for safety and are available in a number of different sizes to accommodate volume requirements of various testing instruments. The most common CBG tubes are 100 mm in length with a capacity of 100 μL. The inside of the tube is coated with heparin, identified by a green band on the tube.
• Stirrers are inserted into the tube after the blood is collected to aid in mixing the anticoagulant.
• A magnet is used to mix the specimen after both ends of the tube have been sealed. The magnet typically has an opening in the center or side so that it can be slipped over the capillary tube and moved back and forth along the tube length, pulling the metal stirrer with it, and mixing the anticoagulant with the blood.
• Plastic caps or closures are used to seal CBG tubes and maintain anaerobic conditions in the specimen. CBG tubes typically come with their own caps.
• Glass microscope slides are occasionally used to make blood films for hematology determinations.
• Warming the site increases blood flow as much as seven times.
• To avoid burning the patient, the devices provide a uniform temperature that does not exceed 42°C and should only be applied for 3-5 minutes