Retrieving disorders and findings: Results using SNOMED CT and NegEx adapted for Swedish

Access to reliable data from electronic health records is of high importance in several key areas in patient care, biomedical research, and education. However, many of the clinical entities are negated in the patient record text. Detecting what is a negation and what is not is therefore a key to high quality text mining. In this study we used the NegEx system adapted for Swedish to investigate negated clinical entities. We applied the system to a subset of free-text entries under a heading containing the word ‘assessment’ from the Stockholm EPR corpus, containing in total 23,171,559 tokens. Specifically, the explored entities were the SNOMED CT terms having the semantic categories ‘finding’ or ‘disorder’. The study showed that the proportion of negated clinical entities was around 9%. The results thus support that negations are abundant in clinical text and hence negation detection is vital for high quality text mining in the medical domain.