Abstract
OBJECTIVE: To measure the validity of the clinical diagnosis of the basal cell carcinoma (BCC) in primary care. DESIGN: Cross-sectional study. SETTING: Primary health care Area 8 in Madrid. PATIENTS AND ITNERVENTIONS: A study was carried out on a group of patients that had been histopathologically diagnosed of BCC and on another that had received any of the most frequent differential diagnoses. A sample estimate was made with the most unfavourable situation of a sensitivity and a specificity of 50%, a precision of 5%, a confidence of 95% and losses of 20%. It was estimated that 962 cases were necessary. MEASUREMENTS: The histopathological diagnosis (gold standard) were compared to the clinical diagnosis. Sensitivity, specificity, predictive values, likelihood ratios and global value were estimated. RESULTS: 963 patients were included of which 7.6% were lost 890 cases were studied, 491 with BCC and 399 with differential diagnoses. The most frequent location of BCC was the face (65.8%). Sensitivity was 27.5% (95% CI, 23.531.5%), specificity 90.5% (95% CI, 87.5-93.5%), the global value of 55.7% (95% CI, 52.7-58.7%), positive predictive value, 78.0% (95% CI, 72.084.0%) and negative predictive value 50,3% (95% CI, 46.354.3%). CONCLUSIONS: Validity was moderate with low sensitivity and very low positive predictive value, the latter estimated for its expected prevalence. The clinical diagnosis of BCC in primary health care must be complemented with other diagnostic tests.