NTCA - Cost effectiveness of using Quantiferon Gold (QFT-G) versus Tuberculin skin test (TST) at the St. Louis County Department of Health TB clinic among US and Foreign born populations

Screening individuals with QFT-G when the LTBI prevalence rate is low is not cost effective. It is cost effective and should be used on high risk populations such as foreign born individuals.
Ayesha Iqbal1, MBBS, MPH; Jenelle Leighton1, RN, BSN; John Anthony1, MT (ASCP) CIC; 1St. Louis County Department of Health

Early detection and treatment of latent tuberculosis infection (LTBI) is vital to reduce the burden of tuberculosis disease (TB). Numerous studies have compared the efficacy of Quantiferon Gold (QFT-G) and tuberculin skin test (TST) for LTBI screening. Although the TST has been used for decades, these comparative studies show it has low specificity for BCG-vaccinated individuals yielding higher false positive results. In contrast, prior BCG vaccination status has no effect on QFT-G, and no boosting is needed to generate an immune response. Also, QFT-G reduces interpreter bias and requires only one patient visit. The St. Louis County Department of Health is committed to appropriate clinical management of LTBI, and sought to evaluate the use of QFT-G for screening. The main objective of this study was to determine the cost effectiveness of routinely using QFT-G in place of TST at the St. Louis County TB Clinic.

St. Louis County Department of Health`s electronic medical records data from 2006 - 2007 were used. General cost per patient was categorically determined. These costs included administrative, laboratory, radiology, medications, and the TB screening test. Additionally, false positive rates for TST and QFT-G were calculated for US and foreign born individuals.

Clinical data revealed 61% (168) foreign born and 39% (108) US born with LTBI. The median expense on a US born patient with positive TST is 8% higher than a foreign born patient. US born patients were less apt to both decline treatment (3% vs. 19%) and discontinue treatment early (14% vs. 19%). Based on LTBI prevalence rate of 19% and population of 55,000, the estimated false positive rate is 32% for foreign born individuals, when screened with TST. The projected savings for 2008 at this rate with QFT-G was 12%. Based on LTBI prevalence rate of 2% and population of 950,000, the estimated false positive rate is 5% for US born individuals, when screened with TST. The projected cost for 2008 at this rate with QFT-G was 3% higher. Screening individuals with QFT-G when the LTBI prevalence rate is low is not cost effective. It is cost effective and should be used on high risk populations such as foreign born individuals.