Paper Information

Journal:   IRANIAN JOURNAL OF INFECTIOUS DISEASES AND TROPICAL MEDICINE   MARCH 2010 , Volume 15 , Number 48; Page(s) 19 To 22.
 
Paper: 

PREDICTIVE VALUE AND CUT OFF POINT OF PPD IN PROBABLE PATIENTS WITH PULMONARY TUBERCULOSIS

 
 
Author(s):  SOFIAN M.*, MOEINI L., FARAHANI S., KHALILI H., AGHAKHANI A., BANIFAZL M., RAMEZANI A.
 
* 
 
Abstract: 
Background and objective: Tuberculin skin testing (TST) is used for identification of tuberculosis infection.
Interpretation of test is related to many factors such as prevalence of disease in community, use of vaccine, age of patients and exposure to non-tuberculosis mycobacterium. Cut off point of TST is reported between 2 to 16mm in different communities. In this study we aimed to determine the predictive value and cut off point of TST in probable patients with pulmonary tuberculosis (TB).
Materials and methods: A total of 714 probable patients with pulmonary tuberculosis with mean age 57
±20.11 years were included in this study. 52.9% of them were male. All subjects were tested using 5 tuberculin units of purified protein derivative (PPD). Gold standard for diagnosis of TB was considered positive smear or culture. Specificity, sensitivity, positive predictive value (PPV) and negative predictive value (NPV) of TST were determined. Cut off point of PPD was determined using Roc curve.
Results: 113 patients from 714 suspicious subjects (15.82%) had pulmonary tuberculosis.80% of them had positive sputum smear.
Sensitivity, specificity, PPV and NPV for PPD
³5mmwere 80%, 61%, 28% and 94% respectively.
Sensitivity, specificity, PPV and NPV for PPD
³10mm were 53%, 82%, 35% and 90% respectively. The calculated cut off point for PPD was ³4 mm.
Conclusion: Our results emphasized that a TST reaction smaller than 5 mm was seen in patients with bacteriological confirmed pulmonary tuberculosis. Predictably, as the cut-off is moved to larger reactions, sensitivity decreases and specificity increases. More estimates are needed to identify the accurate cut off point of PPD in tuberculosis patients.
 
Keyword(s): PREDICTIVE VALUE, PPD, CUT OFF POINT
 
References: 
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