Tonsillitis laboratory findings: Difference between revisions
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==Overview== | |||
==Laboratory Findings== | |||
The diagnosis of GABHS tonsillitis can be confirmed by culture. Samples are obtained by swabbing both tonsillar surfaces and the posterior pharyngeal wall are plated on sheep blood agar medium. The isolation rate can be increased by incubating the cultures under anaerobic conditions and using selective media. A single throat culture has a sensitivity of 90%-95% for the detection of GABHS. False-negative results are possible if the patient received antibiotics. The identification of GABHS requires 24 to 48 hours. The use of bacitracin disc provides presumptive identification. Attempts to identify beta hemolytic streptococci other than group A may be important in adults. Commercial kits containing group-specific antisera are available. Rapid methods for GABHS detection (10–60 minutes), are available. Older antigen tests detect the surface Lancefield group A carbohydrate. Newer tests identify GABHS serotypes using nucleic acid (DNA) probes or polymerase chain reaction. Rapid detection kits have a sensitivity of 85 to 90. Bacterial culture should be performed in cases of a negative rapid streptococcal test.<ref>Leung AK, Newman R, Kumar A, Davies HD. Rapid antigen detection testing in diagnosing group A beta-hemolytic streptococcal pharyngitis.Expert Rev Mol Diagn. 2006;6:761-6.</ref> | |||
True infection with GABHS, rather than colonization, is defined as the presence of >10 colonies of GABHS per blood agar plate. However, this method is difficult to implement because of the overlap between carriers and infected patients. An increase in antistreptolysin O (ASO) streptococcal antibody titer 3–6 weeks following the acute infection can provide retrospective evidence of GABHS infection.<ref>Brook I.Overcoming penicillin failures in the treatment of Group A streptococcal pharyngo-tonsillitis.''Int J Pediatr Otorhinolaryngol''. 2007;71:1501-8.</ref> ASO titers are considered definitive proof of GABHS infection. | |||
When GAHBS is not isolated, the clinician should seek other potential pathogens. However, many of these organisms are part of the normal flora residing in the pharynx, making interpretation of the results difficult. | |||
A finding of a membrane in the throat should prompt a search for [[corynebacteria]]. Culture should be obtained from beneath the membrane, and use of a special moisture-reducing transport medium is necessary. The material may be inoculated on a Loeffler slant, tellurite plate, or blood agar plate. Identification by [[fluorescent antibody]] technique is also possible. | |||
[[Viral cultures]] are available, as well as rapid tests for some viruses (e.g., [[respiratory syncytial viruses]]). A [[heterophile slide test]] or other rapid test for [[infectious mononucleosis]] can provide a specific diagnosis. | |||
==References== | ==References== | ||
{{reflist|2}} | {{reflist|2}} | ||
Revision as of 13:20, 26 September 2012
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Laboratory Findings
The diagnosis of GABHS tonsillitis can be confirmed by culture. Samples are obtained by swabbing both tonsillar surfaces and the posterior pharyngeal wall are plated on sheep blood agar medium. The isolation rate can be increased by incubating the cultures under anaerobic conditions and using selective media. A single throat culture has a sensitivity of 90%-95% for the detection of GABHS. False-negative results are possible if the patient received antibiotics. The identification of GABHS requires 24 to 48 hours. The use of bacitracin disc provides presumptive identification. Attempts to identify beta hemolytic streptococci other than group A may be important in adults. Commercial kits containing group-specific antisera are available. Rapid methods for GABHS detection (10–60 minutes), are available. Older antigen tests detect the surface Lancefield group A carbohydrate. Newer tests identify GABHS serotypes using nucleic acid (DNA) probes or polymerase chain reaction. Rapid detection kits have a sensitivity of 85 to 90. Bacterial culture should be performed in cases of a negative rapid streptococcal test.[1]
True infection with GABHS, rather than colonization, is defined as the presence of >10 colonies of GABHS per blood agar plate. However, this method is difficult to implement because of the overlap between carriers and infected patients. An increase in antistreptolysin O (ASO) streptococcal antibody titer 3–6 weeks following the acute infection can provide retrospective evidence of GABHS infection.[2] ASO titers are considered definitive proof of GABHS infection.
When GAHBS is not isolated, the clinician should seek other potential pathogens. However, many of these organisms are part of the normal flora residing in the pharynx, making interpretation of the results difficult. A finding of a membrane in the throat should prompt a search for corynebacteria. Culture should be obtained from beneath the membrane, and use of a special moisture-reducing transport medium is necessary. The material may be inoculated on a Loeffler slant, tellurite plate, or blood agar plate. Identification by fluorescent antibody technique is also possible. Viral cultures are available, as well as rapid tests for some viruses (e.g., respiratory syncytial viruses). A heterophile slide test or other rapid test for infectious mononucleosis can provide a specific diagnosis.
References
- ↑ Leung AK, Newman R, Kumar A, Davies HD. Rapid antigen detection testing in diagnosing group A beta-hemolytic streptococcal pharyngitis.Expert Rev Mol Diagn. 2006;6:761-6.
- ↑ Brook I.Overcoming penicillin failures in the treatment of Group A streptococcal pharyngo-tonsillitis.Int J Pediatr Otorhinolaryngol. 2007;71:1501-8.