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We thank Dr Connell and colleagues for their interesting letter in response to the 2010 British Thoracic Society guidelines for the management of tuberculosis infection and disease in patients with chronic kidney disease (CKD),1 and for demonstrating their recent experience with both commercially available interferon-γ release assays (IGRA) and the Mantoux tuberculin skin test (TST) in a group of patients with CKD who had been exposed to tuberculosis. This is a welcome addition to the literature which currently remains sparse in this patient group, particularly in the UK.
We note the disappointingly poor completion of the TST (in only 48%) and subsequent reduction in positive TST responses. We can only assume that the patients, who were initially inpatients at the time of contact, subsequently dispersed to be managed in satellite clinics. In the past we have managed this problem by teaching patients and their carers to read the TST and have followed this up with a telephone call 48 h after administration of the Mantoux test. While not ideal, this has worked well for similar patients who live a considerable distance from a centre (H Milburn, unpublished data 2009).
It is interesting that Connell and colleagues did not find any association of any of the three tests with length of exposure to the index case, as suggested in other studies for the IGRA tests but not the TST.2 It is possible that larger numbers would be needed to demonstrate such an association. This study also described the performance of the three tests in a contact tracing situation, so the numbers tested have depended on the numbers thought to have had significant contact with a particular index case.
We are only aware of two published studies on the relative use of all three of these tests in screening3 4 (as opposed to contact with a known index case) in patients receiving haemodialysis, which is important for the management of patients with CKD, particularly before transplantation.1 Both publications favoured the IGRA tests over the TST in this patient group, but also identified limitations with these tests. There is also one large multicentre study in immunocompromised patients currently underway across Europe, and this includes groups of patients with CKD as well as those with solid organ transplants (Tuberculosis Network European Clinical Trials Group). It is hoped that this study will report next year and will give us definitive data on the relative merits of each of the IGRA tests as well as the TST in this complex group of patients.
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