Invasive diagnostic methods for H. pylori infection listed in the Japanese Society for Helicobacter Research guidelines  include the rapid urease test, microscopic test, and culture test. Non-invasive methods include the UBT, blood H. pylori antibody test, and faeces H. pylori antigen test. Among them, the blood H. pylori antibody test is relatively convenient and widely used. A prevailing method for measuring H. pylori antibodies is ELISA.
In this study, we investigated a newly launched kit that can be used with a general-purpose automatic analyser: The L-HP•J test kit. The L-HP•J test can be performed using commercially available automated analysers, such as Hitachi 7180 (Hitachi High-Tech), JCA-BM6050 (JEOL Ltd., Tokyo, Japan), ARCHITECT c16000 (Canon Medical Systems, Tokyo, Japan), and DxC700AU (Beckman Coulter K.K., Tokyo, Japan). The L-HP•J test was launched in April 2016 by FUJIFILM Wako Pure Chemical Corporation and is based on the latex agglutination turbidimetric immunoassay. To our knowledge, this is the first report to evaluate the diagnostic validity of this newly launched kit. We demonstrated that the diagnostic accuracy, sensitivity, and specificity of the L-HP•J test was approximately 95%, and the concordance rate between the L-HP•J test and conventional ELISA was high, with a κ statistic of 0.8444. Although ELISA showed high specificity, the 90% CI lower limits for sensitivity of ELISA did not exceed the threshold value of 85%. In addition to this, ELISA had a significant tendency to give false negative results (P = 0.0129). From these findings, it can be considered that ELISA tends to underestimate the antibody titre, and that the L-HP•J test is a relatively more accurate kit.
The latex agglutination turbidimetric immunoassay is superior to ELISA in terms of throughput and reducing labour and is expected to greatly contribute to rapid testing. Kita et al. demonstrated that the diagnosis of H. pylori infection is improved when two strains from genotypes commonly seen in the Japanese population (#3 and #5)  are used. The L-HP•J test we evaluated in this study used the same two antigens as the chemiluminescent test. Our findings show that the accuracy of the L-HP•J test is not inferior to ELISA and that it has a greater sensitivity. Regarding the false positive and false negative cases detected using the L-HP•J test, all but one false positive case had low-positive titres (between 4 U/mL and 8.7 U/mL). It has been reported that approximately 10% of individuals with low-positive titres detected using the L-HP•J test are uninfected . Thus, we believe that this problem arises due to the established cut-off value. Regarding the false negative cases, there were many subjects with open-type mucosal atrophy. This is because, in patients with severe atrophic gastritis, H. pylori colonisation is decreased or has spontaneously disappeared, resulting in the decrease of serum antibody . It is important to use additional tests, such as the UBT, to diagnose H. pylori infection correctly if the L-HP•J test is not consistent with endoscopic findings, such as in the following two scenarios: (1) when an individual has an open-type mucosal atrophy and endoscopic findings suggest current infection, but the L-HP•J test result is negative; or (2) when endoscopic findings suggest no infection, but the L-HP•J test result has low-positive titres (between 4 U/mL and 8.7 U/mL).
In the present study, we considered both the results of the UBT, which has a high diagnostic accuracy , and endoscopic findings based on the Kyoto classification of gastritis. We then diagnosed the presence or absence of H. pylori infection in those subjects whose UBT results and endoscopic findings were consistent. Therefore, subjects who were previously infected with H. pylori and those who had type A gastritis could be excluded from the study. Moreover, this was a prospective study and antibody measurements using both kits were performed in-house, which increases the reliability of the study.
There are some limitations of the study. First, it represented a single-centre observational study. To confirm the generality of this kit, a multi-centre study is needed in the future. Second, in some subjects, fresh plasma was used for detection using ELISA and part of the L-HP•J test, while stored serum (harvested within 4 weeks) was also used for some of the L-HP•J tests; therefore, there were differences between subjects in terms of the conditions of the specimens used. However, supplemental data from FUJIFILM Wako Pure Chemical Corporation showed no difference in the titres between fresh plasma and stored serum (harvested within 4 weeks) under conditions of -20 °C. Third, we used the UBT as the gold standard for diagnosing H pylori infection; however, its accuracy is not 100% . Fourth, we investigated only non-infected and currently infected cases, not previously infected cases. Therefore, a further study should be conducted to analyse the association between previously infected cases and the antibody titre of the L-HP•J test.