Tonsillitis laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Usama Talib, BSc, MD [2]
Overview
The diagnosis of GABHS tonsillitis is mostly clinical but it 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.[1]
Laboratory Findings
The following laboratory findings can be helpful in diagnosing tonsillitis along with clinical examination:[2]
Complete blood count with differential
- This usually shows leukocytosis with neutrophilic predominance.
Serum electrolytes
- This is useful too in patients presenting with dehydration.
Throat Culture
- Culture is a highly sensitive test used to diagnose bacterial tonsillitis.[3]
- A single throat culture has a sensitivity of 80% and specificity of 100% for the detection of GABHS.[4]
- Streptococci will usually be grown on agar media to produce β-hemolysis for use in identification and specification.[5]
- Streptococcus pyogenes will display as smooth, white-grey domes surrounded by β-hemolysis.
- They will be arranged in chain formation as Gram-positive cocci when examined microscopically.
- Catalase testing will confirm that the isolates obtained through the culture swab represent streptococci infection.
- 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.
- 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.[6]
- 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.[7] ASO titers are considered definitive proof of GABHS infection.
- When GABHS 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
- ↑ Template:Ruuskanen, Olli, et al. "Rapid diagnosis of adenoviral tonsillitis: A prospective clinical study." The Journal of pediatrics 104.5 (1984): 725-728
- ↑ Blair AB, Booth R, Baugh R (2015). "A unifying theory of tonsillitis, intratonsillar abscess and peritonsillar abscess". Am J Otolaryngol. 36 (4): 517–20. doi:10.1016/j.amjoto.2015.03.002. PMID 25865201.
- ↑ Johansson, L.; Mansson, N.-O. (2003). "Rapid test, throat culture and clinical assessment in the diagnosis of tonsillitis". Family Practice. 20 (2): 108–111. doi:10.1093/fampra/20.2.108. ISSN 0263-2136.
- ↑ Fox, J. W.; Marcon, M. J.; Bonsu, B. K. (2006). "Diagnosis of Streptococcal Pharyngitis by Detection of Streptococcus pyogenes in Posterior Pharyngeal versus Oral Cavity Specimens". Journal of Clinical Microbiology. 44 (7): 2593–2594. doi:10.1128/JCM.00797-06. ISSN 0095-1137.
- ↑ Ferretti JJ, Stevens DL, Fischetti VA, Stevens DL, Bryant AE. PMID 26866211. Missing or empty
|title=(help) - ↑ 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.