Comparison of qualitative and quantitative blood determinations in stools of healthy persons and patients with colorectal tumours

Abstract

The possibility of using fecal blood determination for early diagnosis of colorectal cancer is based on the fact that in most cases bleeding from the tumour occurs early in the asymptomatic phase of the disease. The qualitative Haemoccult test is now regarded as most suitable for screening. The test is cheap and simple, but its drawback is a high per cent of false negative and false positive results. Therefore there is a need to look for other methods of greater sensitivity and specificity. One of these methods may be quantitative determination of blood in stools. The purpose of the present study is: 1) to assess the specificity of quantitative fecal blood determinations, 2) to compare the sensitivity of the qualitative and quantitative tests for the detection of colorectal neoplasms. Quantitative blood determination included the heating of stool samples with citric and oxalic acids. The citric acid reagent caused passing into the solution of the so called intestinal porphyrin fraction which is produced from haem spontaneously in the upper gastrointestinal tract. The oxalic acid reagent converts in vitro haem remaining in the stools to porphyrins, without changing the structure of the intestinal-fraction porphyrins. The obtained solutions were subjected to three-phase extraction for removal of non-porphyrin substances. The concentration of porphyrins was read in a spectrofluorimeter at 402 nm excitation wavelength and 600 m emission wavelength. Haemoccult II test was used for qualitative blood determination in three consecutive stools. The result was considered as positive if the colour of the test slide was changed to blue within 30 seconds, at least in one of the six test "windows".(ABSTRACT TRUNCATED AT 250 WORDS)