Does the mass of sample loaded affect faecal haemoglobin concentration using the faecal immunochemical test?

Background Quantitative faecal immunochemical tests (FIT) for haemoglobin are being used for colorectal cancer (CRC) screening for asymptomatic populations and are being indicated as a suitable test to rule out CRC in symptomatic populations. Faecal samples are typically collected by patients using a probe attached to the cap of a device which is inserted into a collection device into the preservative buffer, passing through a collar to remove excess sample: this process has potential for pre-analytical error. This study investigates whether faecal haemoglobin concentration (f-Hb) results are affected by the mass and method of sample collection. Methods Faecal samples with detectable f-Hb were loaded into collection devices from four manufacturers using increasing masses of sample. The f-Hb in the device buffer was measured using the relevant analyser. The results from the minimum recommended load were compared with results of 'sample overloading'. Results The variation in the faecal mass added to the probe (overall CVs: EXTEL HEMO AUTO-MC Collection Picker 300%, OC-Auto Sampling Bottle 3 237%, SENTiFIT pierceTube 264%, Specimen Collection Container A 250%), was more than the variation in f-Hb (respective overall CVs: 62%, 35%, 47%, 39%). The mass of faeces added to the probes increased significantly ( P < 0.0001 for all four devices), but the f-Hb did not increase significantly (EXTEL HEMO AUTO-MC Collection Picker P = 0.6820, OC-Auto Sampling Bottle 3 P = 0.9368, SENTiFIT pierceTube P = 0.7551, Specimen Collection Container A P = 0.6864). Conclusion The mass of sample loaded onto the probe did not impact the f-Hb significantly using all four tested devices.