How to assess the relative range of two consecutive laboratory measurements to monitor patients

Serial determination of CEA and CA 15.3 in breast cancer follow-up: an assessment of their diagnostic accuracy for the detection of tumour recurrences

We studied the diagnostic accuracy of carcinoembryonic antigen (CEA) and cancer antigen 15.3 (CA 15.3) in detecting breast cancer recurrence. Biomarker follow-up determinations, made over 900 patients, were related to local-regional or distant recurrence using statistical models for longitudinal data. The diagnostic accuracy was quantified in terms of sensitivity, specificity and Youden index. The biomarkers were poorly predictive of local-regional recurrence. As for distant recurrence, the best diagnostic accuracy was obtained considering the two biomarkers jointly and combining two positivity criteria: a value above the normal limit or a difference between two consecutive measurements greater than the critical difference for at least one biomarker. A third criterion, based on within-patient comparison between follow-up determinations and a baseline, failed to improve the above result. CEA and CA 15.3 might play a role in patient monitoring during follow-up for the search of distant recurrence.