Capillary collection should not be performed on adult patients if adequate veins are available and patient is willing to allow their use. Also, capillary collection should be avoided if patient is dehydrated, has edema, or presents with poor circulation to the extremities. Blood collected from an edematous (swollen) site will be contaminated with tissue fluid. Dehydration and poor circulation would also interfere with capillary blood flow and patients presenting with one of these conditions would not be good candidates for capillary blood collection.
Certain tests cannot be performed on capillary blood due to the large volume they require or the possibility of contamination. These include the following:
- Westergren erythrocyte sedimentation rate (ESR) test, due to large blood volume required.
- Coagulation studies that require large plasma specimens, due to contamination with interstitial fluid which promotes clotting.
- Blood cultures, due to large volume of blood required and the possibility of skin flora contamination.