Tuberculosis screening in dialysis patients--is the tuberculin test effective?

AIM

Patients with end-stage renal disease are at increased risk for tuberculosis (TB). The Centers for Disease Control and Prevention (CDC) has recommended annual skin testing for TB, with tuberculin-purified protein derivative (PPD), in patients with chronic renal failure. The aim of this study was to identify the incidence and prevalence oftuberculin positivity and assess the utility of the tuberculin test in an inner city dialysis population.

METHODS

All patients on chronic hemodialysis at a center affiliated to the University of Chicago, who were tuberculin-tested between 1997 and 2000 or had previously documented PPD positivity precluding retesting, were included. Demographics, comorbidity, and tuberculin and anergy reactivity were recorded. A positive PPD was an induration of > 10 mm in response to 5 tuberculin units of PPD, and anergy an induration of < 2 mm in response to the anergy antigens (Candida and Mumps), at 48 h. PPD-positive patients were compared with PPD-negative patients; Fisher's exact test and t-test were used, p < 0.05 was considered significant.

RESULTS

Of 131 patients at the dialysis center, 118 were studied. The remaining 13 refused consent to PPD testing. 41 (35%) were PPD-positive, 77 (65%) were negative. Of the 77 PPD-negative patients, 62 (81%) were anergic. None of the PPD-positive patients had clinical or radiographic signs of active TB. Only 20 patients received INH prophylaxis, the others refused or had contraindications to therapy. The conversion rate ranged from 3 - 8% per year. Demographics, nutritional parameters, comorbidity and adequacy of dialysis did not help predict PPD positivity.

CONCLUSION

There is a high prevalence of PPD positivity and anergy among dialysis patients. As the diagnostic utility of the time-tested PPD test is unclear in an anergic dialysis population, the need for a high index of suspicion for active tuberculosis and timely diagnostic work up should be reinforced and not replaced by total dependence on the tuberculin test.