Sputum, expectorated

Objectives: Aetiological diagnosis of lower respiratory tract infection by microscopic examination and culture with identification and susceptibility test of the isolated organism(s). In some countries sputum may also be used for the microscopic demonstration of bronchopulmonary parasites, such as the ova of Paragonimus spp. and larvae of Strongyloides stercoralis.

Test material: Secretion from the lower respiratory tract produced by coughing.

Collection time: Before the patient has received antibiotic treatment.

Equipment: Clean, wide-mouthed screw-capped container (minimum content 25 mL).

Procedure: Instructions should be given to the patient beforehand by a nurse or a laboratory technician.

1. The patient should be standing, if possible, or sitting upright in bed.

2. He or she should take a very deep breath to fill the lungs, and empty them in one breath, coughing as hard and as deeply as possible.

3. The sputum brought up should be spit into the container.

4. If the quantity of sputum is not sufficient (1-2 mL), the procedure may be repeated. A single well collected specimen, however, is better than a specimen collected over several hours.

5. Before being sent to the laboratory, the specimen should undergo a brief visual evaluation and its appearance should be recorded on the request form.

6. Tighten the cap on the container and send the specimen immediately to the laboratory.

Sample quantity: 1-2 mL.

Storage: Refrigerated (2-8 °C).

Transportation: In a cooling box (2-8 °C) except when the transport time is less than one hour.

Reporting: Isolation of a possible pathogen can be expected after 2-3 days. Negative cultures will be reported out 1-2 days after receipt of the specimen.

Comments: The sputum will be examined by microscopy before it is cultured. If the specimen only or mainly consists of saliva, it will not be processed further, and the request form will be returned to the department with the statement "Improper specimen, only saliva, please resubmit". If the specimen contains lower respiratory secretion with signs of inflammation (more than 10 polymorphonuclear neutrophils per squamous epithelial cell), the pathogenic organisms will be identified and tested for antibiotic susceptibility.

    All expectorated sputum is contaminated to some degree with secretion of the oropharyngeal cavity, which contains a wide variety of commensal bacteria, some of which are potential pathogens of the lower respiratory tract (pneumococci, Haemophilus influenzae). Since the sputum should reflect the infection in the bronchi and the lung, contamination with oropharyngeal secretions should be kept to a minimum. A good technique for expectoration and collection of the specimen is essential.

    The examination of sputum is not indicated in patients with fever of unknown origin.