CORRESPONDENCE

CRP and toxic granulation

To the Editor: I read the article on CRP and toxic granulation with great interest.¹ The authors concluded: 'The proposed system can be applied to patients with inflammatory or infectious conditions, where grading of toxic granulation of neutrophils can possibly be used as a surrogate marker to assess infection or inflammation and their response to treatment.'¹ I agree that the new system can be useful in clinical practice. However, there are some points of concern. Firstly, the assessment of toxic granulation must be based on experienced clinical microscopy;² this might not be available in rural hospitals. Secondly, there are many confounding factors that can affect the CRP level, and this aspect was not totally controlled in the article.³

Viroj Wiwanitkit
Wiwanitkit House bangkok Thailand 10160
wviroj@yahoo.com

1. Van de Vyver A, Delport EF, Esterhuizen M, Pool R. The correlation between C-reactive protein and toxic granulation of neutrophils in the peripheral blood. S Afr Med J 2010; 100: 442-444.

2. Gulati GL, Hyun BH. Quality control in hematology. Clin Lab Med 1986; 6(4):675-688.

3. Tomiyama R. Factors interfering with CRP assay (from the manufacturer's perspective). Rinsho Byori 2000; 48(8): 760-763.

Dr Van de Vyver replies: Laboratory confirmation of the presence of inflammation can be problematic in certain settings. This is a particular issue in settings where anti-inflammatory drugs - especially corticosteroids - are administered. In this setting, a combination of assays is usually employed to provide a cumulative impression of the presence or absence of infection or inflammation. C-reactive protein (CRP) is a widely utilised assay in the evaluation of inflammation. As with most immune assays, various factors can theoretically interfere with the final value reported. However, this seems to be a significant problem with highly sensitive assays (measuring levels below 10 mg/l)¹ as opposed to assays measuring levels in excess of 10 mg/l.²

We agree that assessment of toxic granulated neutrophils requires an experienced technologist, unfortunately not generally available in rural areas. The system is also potentially labour-intensive, with reproducibility highly dependent on the training of the examiners.

Toxic granulation can only serve as an additional tool to assess the presence of infection if there is diagnostic uncertainty. As a single parameter, it is of limited diagnostic value and can serve purely as a contribution to other infective markers.

1. Tomiyama R. Factors interfering with CRP assay (from the manufacturer's perspective). Rinsho Byori 2000; 48(8): 760-763.

2. Wilkins J, Gallimore JR, Moore EG, Pepys MB. Rapid automated high sensitivity enzyme immunoassays of C-reactive protein. Clin Chem 1998; 44: 1358-1361.