Ask the treatment expert ... about wound cultures
Rosalyn Jordan, RN, BSN, MSc, CWOCN, WCC
Are wound cultures the best method to determine if a wound is infected?
According to the National Pressure Ulcer Advisory Panel, the number of bacteria within the wound bed provides the best indicator of infection in a wound. The gold standard for a wound culture is a tissue biopsy because this procedure provides an understanding of the wound tissue and not simply of bacteria on the surface of the wound.
This procedure is performed by taking one gram of tissue from the central area of the wound by a “punch biopsy.” The sample tissue undergoes laboratory studies to identify the offending bacteria and the number of bacteria. The wound is considered infected if the colony forming bacterial count is 105.
All wounds are contaminated with multiple bacteria. Thus, swab cultures may only provide information related to the actual surface of the wound bed and may not be indicative of wound infection. Wounds may not exhibit the usual signs and symptoms of infections such as odor, erythema, increased temperature, edema or pain. In many cases, the wound might not heal.
A “punch biopsy” may not be practical. Therefore, there are two additional types of cultures. Wound fluid aspiration is more accurate than a swab culture but less accurate as a “punch biopsy.”
If you do a swab culture, use the “Levine Method.” The area should first be debrided and irrigated with a pressure of 4- to 12-PSI prior to the procedure. Use alginate swabs rather than cotton or rayon swabs. If the wound is dry, it should be moistened with a saline solution.
Finally, the swab should be depressed into the center of the wound bed. Hold the pressure to express wound fluid from the deeper tissue, rotate the swab at 180 degrees in a 1-centimeter area and hold pressure again so that wound fluid is expressed to the other side of the swab.