Validation of histological diagnoses in a national cervical screening register

Background. Monitoring and evaluation of cancer screening programmes require accurate data on invitations, visits, test results, diagnoses and management. The purpose of this study was to evaluate the completeness and accuracy of histological diagnoses (cervical precancerous lesions and cancer) in the Finnish cervical cancer screening register by comparing data with the cancer register and the administrative hospital discharge register. Material and methods. Screening data covering all 16 353 screening episodes that resulted in a referral for colposcopy over the period of 1998-2007 were individually linked with hospital discharge and cancer register data using the unique personal identifier. Agreement between registers, as well as sensitivity, coverage and positive predictive values (PPV) for the screening register and the hospital discharge register diagnosis, were estimated. Invasive cases in the cancer register and pooled cases of precancerous lesions were used as reference case populations. Results. The sensitivity of the screening register for cervical cancer was 69%, the coverage 100% and the PPV 77%. Corresponding values for the hospital discharge register were 81%, 100% and 83%, respectively. Sensitivity of the screening register for cervical intraepithelial neoplasia grade 2 or worse (CIN2+) against the pooled case population was 89% and coverage 99%. Corresponding values for the hospital discharge register were 78% and 93%. Kappa-values for pair-wise agreement between the three registers ranged between 0.73 and 0.79, often the lesion grade was lower in the screening register than in the other two registers. Conclusions. The data in the screening register has high coverage and is thus useful for statistical and evaluation purposes. However, in order to improve the accuracy of diagnostic information, there are grounds to consider data retrieval through systematic linkage to other health care registers.