Precision of tuberculosis diagnosis codes in the Central Denmark Region

INTRODUCTION: Correct use of tuberculosis (TB) diagnosis codes is essential for patient care, surveillance and resource allocation. We aimed to assess the positive predictive value (PPV) of TB diagnosis codes.

METHODS: In this retrospective cohort study, we identified patients with International Classification of Diseases, tenth version (ICD-10) TB diagnosis codes from 1 July 2020 to 30 June 2023, at two TB centres in the Central Denmark Region. Confirmed TB was defined as microbiologically confirmed TB, prescription of ≥ 3 first- or second-line TB drugs, or TB notification. All patients who did not meet these criteria and those who received fewer than three TB drugs or lacked TB notification underwent manual hospital record review to verify or exclude the TB diagnosis. PPVs were calculated as the proportion of confirmed TB diagnoses among all patients with a TB diagnosis code.

RESULTS: In total, 185/230 patients were confirmed to have TB, yielding a PPV of 80% (95% CI: 75; 85). The PPVs for TB microbiology, TB prescriptions and TB notification exceeded 95% individually. Excluding TB lupus codes increased the PPV to 89% (95% CI: 84; 93). Patients with more than one different type of TB diagnosis code had a PPV of 100% (95% CI: 93; 100). Additionally, PPVs were high when TB diagnosis codes appeared on multiple occasions, increasing with the number of occurrences (≥ 2: 85%, ≥ 3: 89%, ≥ 4: 93%).

CONCLUSION: TB ICD-10 diagnosis codes demonstrate a moderately high PPV in Denmark, particularly when excluding TB lupus codes, highlighting the importance and complexities of diagnostic coding.

FUNDING: None.

TRIAL REGISTRATION: Not relevant.