FOBTs are considered positive above a certain cut-off value. As a rule, only people whose test is above the cut-off are referred to colonoscopy. A Dutch study with over 260,000 participants has now investigated whether negative results - i.e. those that did not reach the cut-off value - could also have a prognostic relevance.
The study included people who had had two FOBTs two years apart that had turned out negative. After a retest, 3.3% of the participants had a positive result above the cut-off value. Over the course of the study, 1.2% of the study population were diagnosed with advanced adenoma, and 0.2% with colorectal carcinoma.
The researchers found that the level of haemoglobin in the stool sample was associated with the risk of carcinoma. Thus, those whose result was higher in the first two (negative) samples had a significantly higher risk of developing malignancy. Therefore, the probability of cancer was highest in the group with just below the cut-off mark.
The study results impressively show that the fecal occult blood test has clinical relevance even below the threshold value. The level of haemoglobin correlates with the risk of carcinoma.