Reliable capillary sampling of carcinoembryonic antigen at home: the CASA feasibility study

Follow-up after colorectal cancer requires frequent surveillance of the tumour marker carcinoembryonic antigen (CEA). Home-based blood sampling could be beneficial in terms of patients' well-being and societal cost-effectiveness. Blood sampling by venepuncture is unsuitable for home-based sampling. The aim of this feasibility study is to evaluate the long-term whole-blood stability of CEA.

In this prospective feasibility study capillary blood withdrawal was collected in a Hem-Col^® microtube containing a patented stabilization buffer using an internal lithium standard to correct for dilution. Long-term whole-blood stability was considered adequate if the relative bias in CEA concentration between delayed analysis of capillary samples and directly processed venepuncture is within the total error margin of CEA.

Twenty two colorectal cancer patients were included to determine the stability of CEA in capillary sampling compared with directly processed (i.e. within 2 h) venepuncture sampling. The median time between venous sampling and CEA analysis and capillary sampling and CEA analysis was 2 h (interquartile range 1-4 h) and 76 h (interquartile range 74-95 h), respectively. A Bland-Altman difference plot excluding outliers showed an overall relative bias of -1.23%. The two capillary samples in our outlier analysis also showed the highest lithium concentrations.

Home-based capillary sampling with the use of the Hem-Col^® buffer is a feasible method for CEA determination when analysed within 4 days after blood withdrawal, allowing monitoring for colorectal cancer patients from home. High lithium concentrations due to insufficient filling of the Hem-Col^® tube suggest less reliable CEA measurements.