Aim: Anti-Helicobacter pylori (H. pylori) antibody titers of four serum antibody kits were measured simultaneously up to 6 years in order to clarify the usefulness in the detection of past infection for the screening of gastric cancer risk and the possibility of unnecessary eradication in patients with successful eradication.

Subjects and methods: The study included 239 subjects (66.0 ± 9.3 years old, male 117, female 122) who were enrolled in a multicenter study. Serum samples were obtained at least three times during a 6-year period after successful eradication. Anti-H. pylori antibody titers were measured for each serum sample using three Latex aggregation immunoassay (LA) kits and one enzyme immunoassay (EIA) kit simultaneously, and the changes in antibody-positive rate were compared.

Results: Seropositivity of each kit at 1 to 6 years after eradication was as follows. LZ test: 58.9, 45.1, 45.0, 35.5, 38.7, and 40.4%. Denka latex “Seiken”: 63.9, 52.4, 39.6, 36.2, 35.1, and 27.7%. L-type Wako: 75.7, 61.6, 55.0, 53.9, 48.8, and 40.4%. E-plate (EIA kit): 72.8, 62.2, 48.6, 45.4, 38.7, and 34.0% when the cut-off value was set at 3.0 U/mL and 10.4, 4.3, 4.5, 5.7, 4.2, and 2.1% when cut-off value was set at 10.0 U/mL.

Conclusions: Compared to the EIA kit, antibody titers of the LA kits remained higher than cut-off value for longer years after eradication. LA kits might be more useful to identify past infection in mass surveys. However, serum antibodies are often measured in subjects after successful eradication. It is important to perform appropriate diagnostic tests to avoid unnecessary eradication when LA tests show positive results.

In the countermeasure-type colorectal cancer screening program in Hamamatsu City, the Hamamatsu Medical Association, which is entrusted with the screening program, launched the Colorectal Cancer Screening Committee in 2019 and began accuracy management. As part of this effort, we analyzed data from 2015 to 2020 and conducted surveys of facilities that perform fecal occult blood tests and testing companies that received orders. It was found that the recall rate ranged from 7.4 to 8.3%, and the rate of responders for recall ranged from 53 to 63%, neither of which reached the allowable values. Further, the recall rate was highly variable among institutions, with the main reason for this being that the cut-off value of fecal occult blood was not uniform, with a wide variation of 50 to 150 ng/ml. Therefore, we changed the description of fecal occult blood test results on colorectal cancer screening forms from the conventional qualitative values to quantitative values, unified the cut-off value to 130 ng/ml, and implemented the changes in April 2022. As a result of a 1-year study, it was found that the recall rate was 6.0%, which was below the acceptable value of 7.0% for the first time, confirming that the changes were effective. To improve the proportion of responders for recall examination, the new screening form includes measures such as adding a column to confirm the intention to undergo colonoscopy when a patient is found to require a checkup and asking the examinee to check the box. The use of this new screening form is expected to facilitate appropriate colorectal cancer screening operations in the future.