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Three Part Question

In [children presenting with acute hip pain] is [a C reactive protein] useful in [diagnosing septic arthritis]

Clinical Scenario

A 7 year old child presents to the emergency department with a short history of a limp, temperature and difficulty in weightbearing on the right leg. The pain seems to be localised to the hip. You wonder whether a C reactive protein (CRP) measurement will help in excluding the diagnosis of septic arthritis.

Search Strategy

Medline 1966-02/04 using the OVID interface.
{(exp child OR children.mp OR exp pediatrics OR paediatr$.mp) AND (exp arthritis, reactive OR exp arthritis, infectious OR arthritis.mp OR exp arthritis) AND (exp laboratory techniques and procedures OR exp c-reactive protein)} LIMIT to human and english.

Search Outcome

Altogether 107 papers found of which only 3 were found to be relevant. These papers are shown in the table.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Eich GF et al, 1999, Switzerland	89 children with acute hip pain	Diagnostic test	Septic Arthritis CRP > 10 mg/ L	Sensitivity 100% specificity 76%	Retrospective chart review, 25 out of 114 patients excluded, not all received gold standard arthocentesis. Only 8 patients with septic arthritis giving wide confidence intervals
Kunnamo et al, 1987, Finland	278 children with arthritis initially presenting to primary care	Diagnostic test	Septic Arthritis CRP > 10 mg/ L	sensitivity 100% specificity 46% based on scatter plot provided	Retrospective chart review, multiple joints and pathologies represented, not all received gold standard arthocentesis
Levine et al, 2003, USA	133 children hospitilised for arthritis and who had undergone joint aspiration	Diagnostic test	Diagnostic test Septic Arthritis CRP > 10 mg/ L	sensitivity 90% specificity 29%	Retrospective chart review, only 24% of study group had hip diesase, endemic Lyme disease

Comment(s)

A limping child is a common presentation to the emergency department. Septic arthritis is just one of many possible diagnoses, but one for which the consequences of failure to recognise may be disastrous. The gold standard for diagnosis is the aspiration of hip effusions, with microscopy and culture of the fluid drawn off. Since the most common cause of hip effusion in children is transient synovitis, which usually follows a fairly benign course, aggressive investigation of all effusions is inappropriate. The evidence shows that limping children with a hip effusion and a CRP <10mg/ml are extremmely unlikely to have septic arthritis and are therefore suitable for a more conservative approach. The papers reviewed are of fairly poor quality and more work on the subject is warranted.

Clinical Bottom Line

An isolated CRP measurement <10mg/ml can be used as a reliable rule out tool for septic arthritis

References

1. Eich GF, Superti-Furga A, Umbricht FS, Willi UV. The painful hip: evaluation of criteria for clinical decision making. Eur J paediatr 1999;158(11):923-8.
2. Kunnamo I, Kallio P, Pelkonen P, Hovi T. Clinical signs and laboratory tests in the differential diagnosis of arthritis in children. Am J Dis Child 1987;141(1):34-40.
3. Levine MJ, McGuire KJ, McGowan KL, Flynn JM. Assessment of the test characteristics of C-reactive protein for septic arthritis in children. J Ped Orth 2003;23(3):373-7.