A validation study of the identification of haemophagocytic lymphohistiocytosis in England using population-based health data

Summary We assessed the validity of coded health care data to identify cases of haemophagocytic lymphohistiocytosis (HLH). Hospital Episode Statistics (HES) identified 127 cases within five hospital Trusts 2013-2018 using ICD-10 codes D76.1, D76.2 and D76.3. Hospital records were reviewed to validate diagnoses. 73/74 patients with confirmed/probable HLH were coded D76.1 or D76.2 (positive predictive value 89.0% [95% CI 80.2-94.9%]). For cases considered not HLH, 44/53 were coded D76.3 (negative predictive value 97.8% [95% CI 88.2%-99.9%]). D76.1 or D76.2 had 68% sensitivity in detecting HLH compared to an established active case finding HLH register in Sheffield. Office for National Statistics (ONS) mortality data (2003-2018) identified 698 patients coded D76.1, D76.2 and D76.3 on death certificates. 541 were coded D76.1 or D76.2 of whom 524(96.9%) had HLH in the free text cause of death. Of 157 coded D76.3, 66(42.0%) had HLH in free text. D76.1 and D76.2 codes reliably identify HLH cases, and provide a lower bound on incidence. Non-concordance between D76.3 and HLH excludes D76.3 as an ascertainment source from HES. Our results suggest electronic health care data in England can enable population wide registration and analysis of HLH for future research.