Blumenfeld et al made the following recommendations when selecting a site to collect blood from the foot of a neonate or young infant:
(1) The acceptable sites are
(1a) the most lateral and medial aspects of the plantar surface. In the heel this should be beyond the limits of the calcaneus.
(1b) the middle of the plantar surface of the great toe away from any phalangeal bone.
(2) Unacceptable sites are:
(2a) the posterior curvature of the heel.
(2b) a previous puncture site (which may be infected).
According to Blumenfeld et al, the depth of penetration should be no more than 2.4 mm (with no compression used).
As pointed out by Reiner et al, some compression is almost always used when making the stick, so that the depth of 2.4 mm may be excessive. The lower limit for depth is 1 mm but this may require a longer incision to provide adequate blood flow.
Warming the heel can increase blood flow to the area and can increase the likelihood of success. Commercial "heel warmers" can be used for this purpose.
Factors that may limit the ability to collect blood from the foot:
(1) presence of a cast covering the foot
(2) severe foot malformation
(3) impaired perfusion to the lower extremity
(4) numerous previous puncture sites (no unused sites)
(5) cellulitis or infection
(6) callus formation (develops after 6 months of age)
