Background To diagnose gout, the golden standard is detection of monosodium urate (MSU) crystals in synovial fluid [1,2]. However, while some gout classification criteria include this variable, most gout diagnoses are based on clinical features [3,4]. This discrepancy between clinical practice and classification criteria hampers gout epidemiological studies.
Objectives The objective was to validate gout diagnoses (ICD-10 gout codes) in primary care (PC) and secondary care relative to five classification criteria (Rome , New York , ARA , Mexico , and Netherlands ). The frequency with which MSU crystal identification was used to establish a gout diagnosis was also determined.
Methods In total, 394 patients with ≥1 ICD-10 gout diagnoses in 2009–2013 in Gothenburg, Sweden were identified from medical records of two PCs (n=262) and one secondary care center (n=132). Medical records were assessed for all classification criteria.
Results PC patients met criteria cut-offs more frequently when ≥2 gout diagnoses were made. However, even then, few PC patients met the Rome and New York cut-offs (19% and 8%, respectively). ARA, Mexico, and Netherlands cut-offs were met more frequently by PC patients with ≥2 gout diagnoses (54%, 81%, and 80%, respectively). Mexico and Netherlands cut-offs were met frequently by the rheumatology department patients even when patients with only 1 gout diagnosis were included (80% and 71%, respectively). MSU crystal analysis served to establish gout diagnosis in only 27% and 2% of rheumatology department and PC cases, respectively.
Conclusions If a patient is deemed to have gout when ≥2 PC or ≥1 rheumatology-center visits associate with an ICD-10 gout code, the positive predictive value of this variable relative to the Mexico and Netherlands classification criteria was ≥80% in both PC and rheumatology care settings in Sweden. MSU crystal identification was rarely used to establish gout diagnoses.
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Disclosure of Interest None declared