Thumb-skin punctures

Medical Laboratory Observer, Dec, 2004 by Dennis Ernst

Q One of our phlebotomists said that you should never poke a thumb for a capillary sample. I know it is not the usual site, but is it absolutely prohibited? What about the big toe? Can you consider exceptions on a case-to-case basis, such as burn patients?

A On adults and older infants, the recommended sites are the fleshy pads (not the sides) of the middle and ring fingers. According to NCCLS, the index finger is not recommended because it is more sensitive and calloused than the other fingers. The thumb is not recommended because it has a pulse, and the skin of the "pinky" is too thin. (1) Punctures to the recommended sites should not be performed parallel to the fingerprints but across them. The big toe is no longer a recommended site for skin punctures in the latest NCCLS skin-puncture standard. Not that it poses a risk, but with a multitude of alternative sites available, it was dropped from the list.

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Reference

1. National Committee for Clinical Laboratory Standards (NCCLS). Procedures for the collection of diagnostic blood specimens by venipuncture. Approved Standard. 5th ed. NCCLS Document H3-A5. Wayne, PA: NCCLS; 2003.

--Dennis Ernst, MT (ASCP)

Director

The Center for Phlebotomy Education Inc.

Ramsey, IN

Edited by Daniel M. Baer, MD

MLO's Tips from the Clinical Experts provides practical, up-to-date solutions to readers' technical and clinical issues from a panel of experts in various fields. Readers may send questions to Dan Baer by e-mail at tips@mlo-online.com.