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Proper collection of specimens is important to maximize the outcome of laboratory tests for the diagnosis of infectious diseases A variety of laboratory tests can be performed to make a presumptive or definitive diagnosis so that therapy can begin.
Blood Culture Normally a sterile body fluid. Specimens obtained by venipuncture are preferred over sampling from vascular catheters unless testing for a central line infection. Timing is determined by the patients clinical condition and should be indicated by the ordering clinician.
Usually collection is spaced over 24 hours. Aseptic technique is essential to avoid contaminating the specimen with organisms colonizing the skin. Cleanse the venipuncture site with 2% chlorhexidine gluconate or povidone-iodine and allow to dry. In case of allergy, use 70% alcohol.
The diaphragm tops of the culture bottles are not sterile and must be wiped with alcohol before injection of blood.
Urine Culture Normally a sterile body fluid. A clean-catch midstream urine collection provides the best method for obtaining a specimen to detect a UTI Patients who are catheterized should have the specimen withdrawn using a sterile syringe from the catheter sampling port
Urine specimens must be transported to the laboratory promptly. If not cultured within 30 mins of collection, urine must be refrigerated and cultured within 24 hrs. Clean-catch midstream urine specimens that have more than 100,000 colonies of bacteria per mL of urine may be indicative of infection. Other types of urine specimens may be collected, such as a straight in-and-out catheter specimen or suprapubic bladder drainage
Stool Culture Obtained to culture organisms that are not part of the normal bowel flora (eg, salmonella, shigella, rotavirus) Patient should defecate into a sterilized container or bedpan. Stool specimens should not contain urine or water from the toilet bowl. Stool specimens can also be obtained directly from the rectum using a sterile swab.
Sputum Culture Specimen needs to be from the lower respiratory tract, not oropharyngeal secretions. The laboratory will perform a Gram stain on all sputum specimens to determine if they are representative of pulmonary secretions. A specimen containing a majority of cells from squamous epithelium will be rejected.
The most common method of collection is expectoration from a cooperative patient with a productive cough Early morning is the optimal time to collect sputum specimens. A sputum specimen can be collected in a sputum trap from patients who have artificial airways and require suctioning.
If a patient cannot produce sputum, sputum induction using an aerosol nebulizer may assist with loosening thickened secretions. Bronchoscopy may be required to obtain sputum if induction fails.
Wound Culture Specimens are cultured for aerobic and anaerobic organisms. Using a sterile swab supplied by the laboratory, collect as much exudate as possible from the advancing margin of the lesion
Avoid swabbing surrounding skin. Place the swab immediately in appropriate transport culture tube and take to the laboratory. Label with the specific anatomic site.
Throat Culture Use a tongue depressor to hold the tongue down. Carefully yet firmly rub swab over areas of exudate or over the tonsils and posterior pharynx, avoiding the cheeks, teeth, and gums. Insert swab into packet and follow directions for handling the transport medium.