Cultures, Sputum and Stool Specimens

Principles of Specimen Cultures and Swab Collections

In the outpatient setting, a medical assistant frequently collects or prepares specimens under the supervision of a licensed provider. A culture is ordered to isolate and identify specific microorganisms that are causing a patient's infection. Antimicrobial susceptibility testing may be performed when a clinically significant organism is isolated and testing is appropriate for that organism and specimen. Susceptibility testing measures an isolated organism’s response to antimicrobial agents in the laboratory; the provider uses those results along with the clinical findings to choose treatment. To ensure the laboratory obtains an accurate picture of the pathogen, culture specimens must ideally be collected prior to the initiation of antibiotic therapy. Initiating antibiotics before collection can suppress the growth of the infectious agent in the laboratory.

Use the aseptic technique and sterile or clean supplies required by the particular specimen-collection protocol to minimize contamination. Medical assistants must follow the exact procedure designated for the specific culture site. For example, some swab collection devices feature transport tubes with an internal medium ampule. When using these systems, the medical assistant must activate the medium ampule after collecting the swab by following the device manufacturer's instructions. Specimen containers must always be labeled in the presence of the patient after verifying two patient identifiers. The label must include the two patient identifiers, the date, the time of collection, and the specific anatomical source. Once labeled, culture specimens must be transported to the laboratory promptly according to facility storage guidelines.

Throat and wound cultures require precise swab placement to avoid collecting normal flora from adjacent tissues. When collecting a throat culture, the medical assistant swabs the tonsils or tonsillar pillars and the posterior pharynx as directed by the collection protocol. During this process, contact with the tongue, cheeks, teeth, and uvula must be strictly avoided. Touching these oral structures contaminates the swab with normal oral flora, which can obscure the true infectious organism.

When delegated to collect a wound culture swab, the medical assistant must target the cleaned, viable wound bed as directed by the provider, rather than collecting superficial drainage. Before swabbing, superficial exudate should be cleaned from the wound using sterile saline. The swab must not touch the intact skin surrounding the wound edges. If a patient requires deep tissue sampling, that procedure is performed by an appropriately qualified clinician rather than the medical assistant.