Unopened sample tubes may be stored at 1-30°C and can be used up to the use-by date stated on the label.
FIT immunochemically detect the globin component in the haemoglobin protein. For this reason, they have a significantly better analytical specificity for human haemoglobin but are sensitive to proteolytic degradation of the haemoglobin protein by microbial proteases in the gut flora. This degradation starts in the gut and continues after the sample has been taken.
Haemoglobin in native faeces (with no stabilising buffer) is highly unstable. Haemoglobin concentrations that had been determined in native faeces by means of various different FIT tests were reduced within a few days to below the detection limit.
The degradation of haemoglobin can be slowed significantly through the use of optimised, stabilising buffer systems, into which the stool sample is transferred by the user as soon as it has been taken. In the case of OC-Sensor FIT, a stabilising sample buffer of this type is integrated into the sample-taking system (OC-Sensor sample tube).
The outstanding efficacy of the OC-Sensor sample buffer system has been confirmed in both internal and external trials.
Stool samples in OC-Sensor sample tubes may be stored, between being taken and their analysis in the laboratory, for one week at room temperature or 28 days under refrigeration.
The period of time in which the samples are exposed to varying temperatures should be kept to a minimum, including but not limited to, the transfer of samples between collection and analysis and the storage of samples at room temperature.
Manufacturer’s statement: For samples that were stored in OC-Sensor sample tubes for 28 days at 2-8o C, a haemoglobin detection rate of 95% ± 14.7 (2 SD) was calculated. After 7 days’ storage at 25oC a detection rate of 96% ± 20.4 (2 SD), while at 30oC 89% ± 20.5 (2S D), was calculated.
The screening test does not directly detect the targeted lesions but instead detects occult human blood in the stool. Thereby these tests provide an indirect indication of the existence of colorectal tumours or their precursors, since these bleed more frequently than healthy intestinal mucosa. The average quantity of haemoglobin detected increases with the progression of colorectal cancer, from a neoplasm with low risk via advanced neoplasms right up to colorectal carcinoma; a direct correlation could be proved between the haemoglobin content in the stool (FIT result) and the appearance of neoplasms. Admittedly the method does not permit any precise statement about the targeted lesion on the basis of the haemoglobin content ascertained.
The haemoglobin content is dependent on age and sex; the haemoglobin content is higher in men and older individuals. This was also able to be determined on the basis of data from three different countries (Taiwan, Scotland and Italy). The FIT data was ascertained using the same test system (OC-Sensor) in all cases and they are therefore directly comparable. In all of the countries a significant correlation was seen between haemoglobin concentrations and age plus gender, however the extent of these differences varied among the countries. This argues for the use of different individual cut-off concentrations.
Furthermore quantitative FIT results in conjunction with other risk factors (age, gender, previous family loading, etc) offer an interesting new possibility for risk stratification and higher accuracy in FIT-based colorectal cancer screening. FIT concentrations are associated with the degree of the histological findings and may improve the predictability in the risk of colorectal neoplasms.
McDonald PJ et al.
Faecal Haemoglobin Concentrations by Gender and Age: Implications for Population-Based Screening for Colorectal Cancer
Clin Chem Lab Med 50/5 (S. 935-40); 2012
Fraser CG et al.
Faecal Haemoglobin Concentrations Vary with Sex and Age, but Data Are Not Transferable across Geography for Colorectal Cancer Screening
Clin Chem Lab Med 52/8 (S.1211-6); 2014