Monday, 18 September 2017

Comparative clinical performance - gFOBT and iFOBT

Many studies comparing iFOBT and gFOBT have been performed in the last 8 years, and several systematic reviews of the literature have been undertaken more recently. 

In 2007 Kerr published a systematic review by the Health Technology Assessment (NZHTA) of New Zealand which had the aim of identifying the international evidence for the clinical and cost effecttiveness of screening tests for colorectal cancer (Kerr et al. 2007). This review included all primary research published as full original reports and secondary research, systematic reviews and meta-analyses published since November 2004. It also included seven eligible primary research papers (Rozen, Knaani & Samuel 1997; Rozen, Knaani & Samuel 2000; Saito et al. 2000; Zappa et al. 2001; Cheng et al. 2002; Cole et al. 2003; Ko, Dominitz & Nguyen 2003) and five eligible secondary research papers; Australian Health Technology Advisory Committee (AHTAC) (1997), Conseil d'√Čvaluation des Technologies de la Sant√© du Quebec (2000), Canada, Craven UK (Craven 2001), Young World Health Organization and World Organization for Digestive Endoscopy (Young et al. 2002), Piper Blue Cross Blue Shield Association Technology Evaluation Center US

The review concluded that “there is limited definitive evidence regarding superior immunochemical FOBT performance over the guaiac tests. However, evidence from cross-sectional studies suggests that the immunochemical test HemeSelect, Beckman Coulter Inc. Fullerton, CA, USA… is comparable, or superior, to guaiac testing… The conclusions on this topic should be revisited if further reliable evidence on the comparative performance of screening FOBTs becomes available”.

A similar conclusion was reached in a systematic review commissioned by the UK NHS and undertaken by the Centre for Reviews and Dissemination of the University of York in 2007 (Burch et al. 2007) which examined the literature until 2004. The review included 59 studies 39 evaluated gFOBTs, 35 evaluated iFOBTs and one evaluated sequential FOBTs. It concluded that there was no clear evidence from direct or indirect comparisons to suggest that guaiac or immunochemical FOBTs performed better. However amongst iFOBTs, Immudia-HemSP (now Hem-SP) appeared to be the most sensitive and specific. 

In the four years since 2004, six studies comparing the performance of gFOBT and iFOBT have been published (Levi et al. 2006; Smith et al. 2006; Allison et al. 2007; Guittet et al. 2007; Dancourt et al. 2008; van Rossum et al. 2008). Some further studies have investigated the accuracy of iFOBTs which, although without a direct comparison with gFOBTs, confirmed the performance of iFOBTs which was reported in the following studies 

In Australia, Smith et al. (2006) performed a paired comparison of an iFOBT (InSure) with a sensitive gFOBT (Hemoccult SENSA); 2351 asymptomatic and 161 symptomatic subjects were requested to perform both FOBTs. iFOBT returned a true-positive result significantly more often in cancer (n = 24; 87.5% vs. 54.2%) and in significant adenomas (n = 61; 42.6% vs. 23.0%) while the false-positive rate for any neoplasia was marginally higher with the iFOBT than the gFOBT (3.4% vs. 2.5%; 95% CI of difference, 0–1.8%): the PPV for cancer and significant adenomas was slightly better for iFOBT (41.9% vs 40.4%). 

In Israel, Levi et al. (2006) compared, a gFOBT with an iFOBT (OC-MICRO, now OC-Sensor) in a small number (151) of patients referred for colonoscopy either because of a positive gFOBT or because they were above average risk of colorectal cancer. Sensitivity, specificity, and positive predictive value for significant colorectal neoplasia were 75%, 34% and 12%, respectively, for gFOBT, and were 75%, 94% and 60% for iFOBT. For a positive gFOBT, 4 times more colonoscopies were needed to identify a significant neoplasm compared with iFOBT, and at more than 4 times greater cost. 

In France, Guittet et al. (2007) compared the performance of gFOBT and iFOBT (Immudia-HemSP (now Hem-SP)) among 10 673 average-risk persons aged 50–74 years. Colonoscopy was offered only if either FOBT was positive. The threshold for a positive iFOBT was varied between 20 ng/mL and 75 ng/mL. Overall, the results depended on the adopted iFOBT threshold. At the lower threshold (20 ng/mL), iFOBT detected 1.5 times as many cancers and nearly 2.6 times as many high-risk adenomas as gFOBT; however, it also increased the relative false-positive rates (2.17 times more frequent for each relevant lesion detected in iFOBT as compared to gFOBT). It is worth noting that at a threshold of 75 ng/mL, iFOBT detected 90% more advanced neoplasms with a significant 33% decrease in the false-positive risk. A further publication from this study (Guittet et al. 2009a) reported that the gain in sensitivity from using iFOBT vis gFOBT was proportional to the degree of blood loss from the lesion and its location. The benefits for cancer detection were restricted to lesion of the rectum.  

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