C‐reactive protein in the emergency department

I read with interest the report of a case of pneumococcal meningitis presenting as ankle pain.¹ Although it discussed the management of an interesting and highly unusual patient, I found it hard to follow the logic of the conclusion that “CRP is an important investigation for emergency departments”.

As the authors state, C‐reactive protein (CRP) is an acute phase protein. Levels of CRP are elevated in the serum of patients with acute and chronic inflammatory, infective, and neoplastic disorders. A recent systematic review by van der Meer et al² examined the evidence pertaining to the contribution of CRP in patients with lower respiratory tract infections (such as pneumococcus). They found in 12 studies reviewed that the relation between an elevated CRP and a bacterial aetiology of the infection was poor: sensitivity ranged from 8–99% and specificity from 27–95%. Other studies in which CRP has been used as a diagnostic tool for other conditions have echoed these findings.

An audit performed by myself in a large teaching hospital emergency department found that between 250 and 500 CRP studies were being requested per month. These were being requested indiscriminately for the full spectrum of presenting conditions, from chest and abdominal pain to one patient that presented with a stab wound! Although individual tests were relatively cheap, because of the numbers being requested the total annual cost to the department was almost £13 000. As a literature review at the time found no evidence to support the use of CRP in the emergency department, departmental policy was altered to prevent the requesting of CRP as routine.

I suspect even the most skilled of emergency physicians may have found the diagnosis of pneumococcal meningitis based on a presentation of ankle pain difficult, with or without a CRP result. As CRP lacks the diagnostic specificity to be of help in the initial assessment of the patient, I feel that it is misleading to advocate its widespread use based on this case alone.