The effect of the variability in fecal immunochemical test sample collection technique on clinical performance.

BACKGROUND Fecal immunochemical test (FIT) performance can be affected by post-collection variables. Collection technique might also affect fecal hemoglobin concentration (f-Hb). Variation in quantity of feces collected in samples returned in a colorectal cancer (CRC) detection program, and the effects of under-sampling, were assessed. METHODS Collection devices obtained from patients undergoing FIT were assessed for the color (in five classes) of the feces in buffer, mass, and f-Hb. Associations between these were examined in an in vitro study on Hb-spiked feces. Variables possibly associated with under-sampling were investigated using multivariable logistic regression. The effect of low sample mass on clinical performance (false-negative results) was determined. RESULTS Of 6,898 samples collected by 3449 individuals (46.9% male, median age: 65.3 years), the buffer was lightest in color in 362 (5.2%), and darkest in 420 (6.1%). Samples with the lightest color had a significantly lower f-Hb compared to all darker classes (p 0.05). Under-sampling related to the lightest color was not associated with false negative results for CRC and advanced adenoma, but was for all neoplasia and inflammatory bowel disease. CONCLUSIONS Wide variation existed in the amount of feces collected. Under-sampling results in lower measured f-Hb and may increase false-negative results. IMPACT Color of sample buffer could be used to identify inadequate sampling.