Refrigerating sputum

Answering Your Questions

Can sputum be refrigerated?

Question

It is common practice now to allow refrigeration of sputum samples prior to processing, in some cases up to 24 hours? Our lab does not allow sputum samples to be refrigerated because of the possibility of loss of possible Neisseria and Haemophilus species. Is refrigerating sputum samples acceptable practice? Are there any studies on this subject?

Answer

The Manual of Clinical Microbiology says sputum can be refrigerated for up to 24 hours or kept at room temperature for up to two hours prior to processing for potential pathogens.¹ There are several studies published on this topic.

Vishniakova and Beliaeva studied respiratory specimens and found that Streptococcus pneumoniae survived four to seven days in specimens stored in a “common” refrigerator (specimen-type dependent), and Haemophilus influenzae could be detected for up to 48 hours.² If stored at 4^0C to 8^0C, more than 88% of S pneumoniae and 85% of H influenzae were still detectable after 24 hours.

Another study by Gould, et al, evaluated sputum specimens stored an additional 48 hours at 4^0C after issue of final results or likewise stored for 48 hours after receipt. Discordant results were seen in 5% to 25% of specimens. These authors concluded that potential respiratory pathogens could survive refrigerated storage.³.

A more recent study by Pye, et al, examined the effect of 24 hours of storage of sputum at 4^0C and 20^0C. These results indicated that the predominant organism could still be recovered following storage at 4^0C and 20^0C, but that viable numbers were reduced by storage at 4^0C in 24% of samples — compared to only 8% in specimens stored at 20^0C.⁴.

—Susan E. Sharp, PhD, D(ABMM)
Director of Microbiology
Kaiser Permanente — NW
Portland, OR

References

1. Thomson RB. Specimen collection, transport, and processing: Bacteriology. In: Manual of Clinical Microbiology. 9th ed. In: Murray PR, Baron EJ, Jorgensen JH, Landry ML, Pfaller MA, eds. Washington, DC: ASM Press;2007:301.
2. Vishniakova LA and Beliaeva NA. Duration of preservation of Streptococcus pneumoniae and Haemophilus influenzae in the sputum and bronchial washings of patients with acute and chronic pneumonias. Zh Mikrobiol Epidemiol Immunobiol. 1982;8:56-59.
3. Gould FK, et al. Does storage of sputum specimens adversely affect culture results? J Clin Pathol 1996;49:684-686.
4. Pye, et al. Effect of storage and postage on recovery and quantitation of bacteria in sputum samples. J Clin Pathol. 2008;61:352-354.

Brad S. Karon, MD, PhD, is associate professor of laboratory medicine and pathology, and director of the Hospital Clinical Laboratories, point-of-care testing, and phlebotomy services at Mayo Clinic in Rochester, MN.