Data quality in the Danish National Acute Leukemia Registry: a hematological data resource

Lene Sofie Granfeldt Østgård,^1,2 Jan Maxwell Nørgaard,¹ Marianne Tang Severinsen,³ Henrik Sengeløv,⁴ Lone Friis,⁵ Morten Krogh Jensen,⁶ Ove Juul Nielsen,⁷ Mette Nørgaard<sup>2

1</sup>Department of Hematology, ²Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark; ³Department of Hematology, Aalborg University Hospital, Aalborg, Denmark; ⁴Department of Hematology, Rigshospitalet, Copenhagen, Denmark; ⁵Department of Hematology, Odense University Hospital, Odense, Denmark; ⁶Department of Hematology, Herlev Hospital, Herlev, Denmark; ⁷Department of Hematology, Rigshospitalet, Copenhagen, Denmark

Background: The Danish National Acute Leukemia Registry (DNLR) has documented coverage of above 98.5%. Less is known about the quality of the recorded data.
Objective: To describe the present coverage of the DNLR, its completeness, and accuracy of individual variables for acute myeloid leukemia (AML). Furthermore, as a second measure of true coverage of the DNLR, to estimate AML incidence in Denmark from DNLR data and compare it to incidence reported from other AML registries.
Patients and methods: By the end of December 2011, the DNLR (established January 2000) included detailed data on a large, well-defined, and nonselected Danish population of 2,665 AML patients. We estimated positive predictive values (PPVs) and completeness for 30 variables, which included patient and disease characteristics, treatment, and treatment outcomes. We identified 260 AML patients (10% of all AML patients recorded in the DNLR). We used information from medical records as the gold standard.
Results: Using the Danish National Registry of Patients as a reference, the coverage of the DNLR was 99.6%. The PPVs of the individual variables ranged from 89.4% to 100%. The completeness of individual variables varied between 60.7% and 100%. Stratification by time of registration in the DNLR (before 2006 versus 2006 and later) revealed higher PPVs and lower frequencies of missing data from 2006. Sex-adjusted incidence rates were 6.2/100,000 person-years (95% confidence interval 5.8–6.6) in males and 4.9/100,000 person-years (95% confidence interval 4.5–5.4) in females. Yearly incidence rates of AML were higher than the incidence rates reported from Sweden (4.5 and 4.2/100,000) and the US (4.5 and 3.1/100,000 in Caucasians).
Conclusion: With few exceptions, there were high values for PPVs and completeness of recorded data. Data accuracy and completeness have improved since the registry was established. The estimated incidence may indicate that the DNLR truly is more complete than other registries. In conclusion, the DNLR is a valuable resource for clinical research of AML.

Keywords: acute myeloid leukemia, incidence, registration completeness, validation studies