A capillary specimen that never reaches the analyzer

At 07:20 an outpatient needs a complete blood count in an EDTA microcontainer and a basic chemistry panel in a lithium-heparin microcontainer. The only available site is a finger, and it is cold and visibly edematous. The collector makes a shallow puncture and squeezes the finger repeatedly to force flow, then partially fills the EDTA container. By 07:23 a clot is visible in that tube. The chemistry container is short filled and visibly hemolyzed.

Neither specimen reaches an analyzer. There is no released result, no unit, and no reference interval to report, because the specimens themselves failed before testing began. Site selection, squeezing, and fill technique can determine whether a capillary specimen is usable.

The flags on this collection tell the story: clot present, short fill, hemolysis, edematous site. Every one of those flags traces back to a decision made at the bedside, not to anything the analyzer did wrong. A clotted EDTA tube cannot give a reliable whole-blood differential or platelet count. A hemolyzed, short-filled chemistry tube cannot be trusted for potassium, LDH, or several other analytes even if enough volume were present.

Capillary collection is the right choice in some situations and not others, a capillary specimen differs from a venous one in composition, and squeezing, site condition, order of draw, and fill volume can turn a small specimen into an unusable one. A difficult venous draw sometimes escalates to capillary collection and sometimes should not. Confirm the site, the device, and the order of fill before touching a lancet, because a small specimen has no margin for a second mistake.