A sufficiently deep incision needs to be made by overcoming tissue resistance to allow formation of 0.5-1ml
of blood ; this is approximately 2.5mm for an adult
(Louis
1999), but different lancets have different settings.
Nurses also frequently use a freehand approach that
can cause pain and interstitial fluid contamination. A
second, deeper cut might need to be made if unsuccessful
the first time. An excessive number of puncture
sites could lead to infection.