The Booster Phenomenon in 2-Step Tuberculin Skin Testing in Hemodialysis Patients

Background: Tuberculosis remains a significant health problem for patients receiving long-term hemodialysis (HD). The greater risk of TB is caused by increase in the likelihood of progression from latent infection to active disease, most likely because of the impaired cell-mediated immunity associated with end-stage renal disease. Consequently routine TB screening of this population is recommended on an annual basis in the dialysis unit. The tuberculin skin test (TST) remains the most useful screening tool.
Objectives: To study the significance and frequency of the booster phenomenon in 2-step tuberculin testing of HD patients.
Methods: Twenty outpatients in the hospital-based hemodialysis center of the children′s Hospital, Cairo University, were screened for tuberculosis with the TST between September and October 2004. To determine the frequency of booster phenomenon, patients with less than 10 mm indurations in the intial TST were given a second test 7 days later. The results were compared with clinical and radiological data.
Results: One of the twenty patients (5%) had a significant tuberculin reaction (≥ 10 mm) on the intial TST. The booster phenomenon was detected in 5 of 19 patients (26.3%) who had a negative reaction (˂ 10mm) to the intial test. These results show the significant rates of TST positively and the booster effect in hemodialysis patients. There was no significant relationship between age, sex, cause of renal failure, hemodialysis duration, serum albumin levels, nor hemodialysis levels with the booster effect. The only significant correlation was detection between serum Ca level and the booster effect (p = 0.014).
Conclusions: The 2-step tuberculin testing procedure may be an effective tool to minimize the booster  effect, thus allowing accurate monitoring of subsequent tuberculin conversion rates in hemodialysis patients thus detecting patients justified for active treatment of TB.