Insufficient classification of anaemia in general practice: a Danish register-based observational study

BACKGROUND: Anaemia can be a pointer of underlying severe disease, including undiagnosed malignancy. Subsequent blood tests are essential to classify the anaemia into subtypes and to facilitate targeted diagnostic investigation to ensure timely diagnosis of underlying disease. OBJECTIVE: We aimed to describe and classify anaemia based on laboratory tests from patients with new-onset anaemia detected in general practice. An additional aim was to analyse associations between patient characteristics and unclassified anaemia (not classifiable according to an algorithm). DESIGN: Population-based cross-sectional study. SETTING: Danish general practice. SUBJECTS: A total of 62,731 patients (age: 40–90 years) with new-onset anaemia were identified in Danish laboratory information systems and nationwide registries, and data were obtained for 2014–2018. MAIN OUTCOME MEASURES: We measured the proportion of patients classified into subtypes of anaemia based on blood tests requested by general practitioners within 31 days of the anaemia index date. RESULTS: Of the 62,731 patients with new-onset anaemia, we identified unclassified anaemia in 78.9% (95% confidence interval (CI): 77.3–80.5) of men and 65.1% (CI: 63.4–66.9) of women. The likelihood of unclassified anaemia increased with age, increasing comorbidity and decreasing severity of anaemia. CONCLUSION: The majority of patients with new-onset anaemia could not be classified through a simple algorithm due to missing blood tests, which highlights a potential missed opportunity for diagnosis. Standardised laboratory testing of patients with anaemia is warranted to ensure adequate follow-up and early detection of underlying severe disease. KEY POINTS: Anaemia can be a sign of malignancy, and anaemia classification is an important step in the diagnosis of underlying disorders. The majority of patients with anaemia could not be classified according to a simple algorithm due to missing blood tests. Some patient characteristics were associated with a high risk of unclassified anaemia: high age, high comorbidity, and severe anaemia. Standardised laboratory testing in patients with anaemia is needed to inform targeted diagnostic investigation to ensure timely diagnosis.