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Three Part Question

In [adults presenting to the ED with an acute hot joint] is [a normal WBC] enough [to rule out septic arthritis]?

Clinical Scenario

A 56 year old woman presents to the ED with a 7-day history of tenderness, swelling and redness of 2 metacarpophalangeal joints and 1 proximal joint in her right hand. She also reports pain and redness of her right knee that makes it difficult to walk. The patient has a 10 year history of RA with intermittent polyarticular flares. On examination, her right knee appears swollen and red. The blood tests you ordered come back with a normal WBC, you wonder is this enough to rule out the possibility of SA?

Search Strategy

Multifile search using OVID – Medline (1950-2008), Embase (1980-2008), CINHAL (1982-2008), Cochrane ({[ exp. Infectious Arthritis OR hot joint.mp OR septic joint.mp OR septic arthritis.mp] AND [ exp. Blood Cell Count, exp neutrophils, white cell count$.mp OR white blood cell count$.mp]}) Limited to Humans, English Language and Adults. Bibliographic References were searched for relevant literature.

Search Outcome

The following number of articles were identified from each of the databases: Medline 118 citations, Embase 125 citations, CINAL 6 citations, Cochrane 2 citations. Two hundred and fifty one articles were disregarded and six papers were critically appraised.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses

Comment(s)

Most of the relevant literature applies to the Paediatric population. From the available evidence, the two recordings of sensitivity are not high enough to rule out septic arthritis (SnNout) and the specificity is not high enough to rule in SA (SpIn). [6, 7]This is supported by studies that report normal WBC in SA. [2-5] The AUC indicates WBC is not a good test at distinguishing (or discriminating) between patients with and without SA. The likelihood ratios (LR) do not seem to help in pointing in the direction of the right diagnosis. The positive likelihood ratio LR (+) is not large enough to rule in a disease and the negative LR (-) is not small enough to rule out a disease. There may be some diagnostic use of it in combination with ESR and joint aspirate WBC (j WBC) as their combined sensitivity is 100% despite their low combined specificity (0.24). [7] Such that if there is no elevation of these three tests, this may be sufficient to rule out septic arthritis when the clinical picture is straightforward and uncomplicated. WBC has been noted as poor, fair test and to have a value purely as an adjunct to the diagnosis of SA along with other ancillary tests. [4, 5, 6]

Clinical Bottom Line

A normal WBC is not sensitive enough to rule out septic arthritis *Imperfect Gold Standard –gram stain (sensitivity 29-50%) and culture (sensitive-82%) [1] References 1. Margaretten ME. Does the Adult Patient Have Septic Arthritis? JAMA 2007; 297(13):1478-1488 2. Li SF. Diagnostic utility of laboratory tests in septic arthritis. Emergency Medical Journal. 2007; 24:75-77 3. Schlapbach P. Bacterial arthritis: Are fever, rigors, and leucocytosis and blood cultures of diagnostic value? Clinical Rheumatology. 1990; 9(1):69-72 4. Peters RHJ. Bacterial Arthritis in a District Hospital. Clinical Rheumatology. 1992; 11(3):351-355 5. Soderquist B. Bacterial or Crystal –associated Arthritis? Discriminating Ability of Serum Inflammatory Markers. Scandinavian Journal of Infectious Diseases.1998; 30:591-596 6. GuptaMN. Sturrock RD, Field M. Prospective comparative study of patients with culture proven and high suspicion of adult onset septic arthritis. Annals of Rheumatological Diseases.2003, 62:327-331

References

1. Li SF, et al Diagnostic utility of laboratory tests in septic arthritis Emergency Medical Journal 2007;75-7
2. Li SF, et al Laboratory tests in adults with monoarticular arthritis: can they rule out a septic joint? Emergency Medical Journal 2004;276-280
3. Schlapbach P, et al. Bacterial arthritis: are fever, rigors, leucocytosis and blood cultures of diagnostic value? Clinical Rheumatology 1990;69-72
4. Peters RHJ, et al Bacterial Arthritis in a district hospital Clinical Rheumatology 1992;351-355
5. Soderquist B, et al Bacterial or Crystal -associated Arthritis? Discriminating Ability of Serum Inflammatory Markers. Scandinavian Journal of Infectious Diseases 1998;591-596
6. Gupta MN, et al. Prospective comparative study of patients with culture proven and high suspicion of adult onset septic arthritis. Annals of Rheumatological Diseases 2003;327-331