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Capillary Blood Gases

In some instances, the health care provider may request an analysis of the capillary blood for blood gases. This is most often requested on infants. Collection of this specimen requires a skilled phlebotomist and specialized equipment.

The patient must be positively identified. All appropriate PPE must be used. The procedure for site selection, preparation and puncture is identical to other infant dermal punctures, however, capillary blood gases are always drawn first if other capillary blood specimens will be collected.

Blood specimens for capillary gases are always collected in long, large-bore heparinized glass tubes. Blood should be drawn into the tube using capillary action. The phlebotomist should start filling the tube using a large well-formed drop of blood, drawing continuously as the blood flows. Each tube must be filled completely end to end as shown in the image on the right. Every effort must be made to avoid drawing air bubbles or air gaps into the tubes as these could adversely affect the results of the test.

Before sealing both ends of the tube, the phlebotomist will insert a tiny metal "flea" into the blood-filled tube and slide a magnet lengthwise back and forth on the outside of the tube. The magnet will cause the flea to move back and forth inside the tube mixing the specimen with the anticoagulant coated on the inside of the tube. This technique should also prevent the blood from clotting, which could result in specimen rejection by the laboratory.

The properly filled glass tubes must be delivered to the analyzing laboratory in a timely manner. Delay in specimen delivery may adversely affect the quality of the patient results.