Blood collection, when only a small sample (1 drop to <1 mL) is needed or when there is difficulty obtaining samples by venipuncture of other sources.
Common capillary blood studies: Complete blood count (CBC), general chemistry labs, bedside glucose estimation, liver function tests, thyroid levels, bilirubin levels, toxicology/therapeutic drug levels, and newborn metabolic screening.
The following laboratory tests are not recommended by capillary blood sampling: Coagulation studies, chromosomal analyses, erythrocyte sedimentation rate, immunoglobulin titers, some other, more sophisticated tests, any tests that require a lot of blood.
Capillary blood gas determination gives satisfactory pH and PCO2, but not PO2.
Blood cultures when venous access or other access is not possible. Sterile technique is required, but heel stick is not the preferred method.
Not recommended for blood sampling in term infants. Most sources confirm that venipuncture, not capillary blood sampling, by a skilled operator is the method of choice for blood sampling in term neonates. Lower pain scores are seen with venipuncture in infants.
Automated self-shielding lancets are preferred in neonates (full-term neonate: incision depth of 1 mm and length of 2.5 mm; preterm neonate: incision depth of 0.85 mm and length of 1.75 mm; see Table 36–1); sterile manual lancets are not recommended but may be used in some units (sizes: 2 mm for <1500 g and 4 mm for >1500 g); capillary collection tube (for rapid hematocrit and bilirubin tests) or appropriate microcollection tubes (if more blood is needed [eg, for chemistry determinations]), preheparinized capillary tubes for blood gas analysis, filter paper card for newborn screening (if appropriate), clay or caps to seal the capillary tube, a warm washcloth with a diaper or heel warming device (eg, a chemically activated packet), antiseptic solution/swabs (alcohol/chlorhexidine swabs); nonsterile or sterile gloves.
Automated self-shielding lancets are preferred in neonates because they are more effective and associated with fewer complications, decreased tissue damage, and in infants with respiratory distress, decreased pain and enhanced cerebral oxygenation. Automated devices cause less hemolysis and less lab value error and provide an exact width and depth of incision. Manual unshielded lancets are no longer recommended (unless automated lancets are not available) because they cause more pain, may penetrate too deeply, and are more likely to injure healthcare providers. Consider vascular puncture if an automatic lancet is not available. There are 2 types of lancet devices: puncture and incision.
Puncture devices. Automated lancets (eg, BD Microtainer contact-activated lancet; Becton, Dickinson and Company, Franklin Lakes, NJ) activate only when positioned and pressed against the skin. These puncture the skin by inserting a blade or needle vertically into the tissue. Puncture-style devices typically deliver a single drop of blood and are better for repeated punctures (eg, for glucose testing). SugarPlum glucose lancet is used to draw just one drop of blood to measure glucose.