Gout diagnoses uncertain when made by general practitioners without serum uric acid testing: an observational study

Abstract

Objective: General practitioners (GPs) diagnose the majority of all gout patients. They make their diagnosis clinically. Serum uric acid (SUA) level >0.35mmol/l is largely determinative for the clinical diagnosis of gout. We aimed to assess to what extent GPs test SUA when making a first gout diagnosis, and to consider consequences regarding diagnostic certainty of not testing it.

Methods: We calculated proportions of patients from 87 Dutch general practices (1-1-2013 to 1-1-2022) with a first gout diagnosis and a recorded SUA test, evaluated if SUA testing was punctually timed with respect to the diagnosis date, whether SUA levels were >0.35 mmol/L, and whether diagnoses corresponded with diagnoses according to the 'Acute Gout Diagnosis Rule' (AGD-rule).

Results: In 43.0% of 7782 patients (mean age 64.4 years; 68.8% male) no SUA test result was recorded, with substantial variation among practices: median 41.9% (IQR 20.2%). 'Gout very likely' according to the AGD-rule was seen in all males and in 83.1% of females when a punctually timed SUA >0.35 mmol/L was present. When such SUA level was lacking, 'Questionable or indeterminate gout diagnosis' was seen in all males and in 67.1% of females, and 'Arthritis diagnosis other than gout' in 32.9% of females.

Conclusion: GPs diagnosed gout without testing SUA in ~40% of cases. This implies avoidable diagnostic uncertainty with impact for the clinical care of many patients as well as for studies that include primary care patients with gout. Key Points • Serum uric acid (SUA) level > 0.35 mmol is determinative when diagnosing gout: however, it is unknown how often SUA testing is applied as such. • More than 40% of patients with a first gout diagnosis according to general practitioners (GPs) had no SUA test result registered in their medical record. • Gout diagnosing by GPs without SUA testing appeared to lead to avoidable diagnostic uncertainty, as diagnoses are often questionable or sometimes even wrong. • Researchers investigating gout need to take into account diagnostic uncertainty if they include gout patients who are diagnosed in primary care in their studies without SUA information.

Keywords: Diagnosis; Diagnostic rule; General practitioner; Gout; Primary care; Serum urate.