Hein JEM Janssens, Lisanne Houtappels, Tjard R Schermer
Affiliation(s):
Radboud University Medical Center, department of primary and community care
Background: Most gout patients are diagnosed in primary care, mainly based on clinical signs and symptoms.[1] In the ‘Gout Calculator’ (or Dutch ‘Acute Gout Diagnosis Rule’) serum uric acid (SUA) level >0.35mmol/L has proven to be a determinatively contributing factor to a positive diagnosis in combination with other specific complaints and symptoms.[2,3] We are not aware of previous studies that have established to what extent general practitioners (GPs) use SUA levels when considering a gout diagnosis, without the availability of MSU crystal identification (the gold standard).
Objectives: We aimed to investigate proportions of patients with a SUA laboratory test result, recorded by Dutch GPs who have made a first gout diagnosis. Moreover, we considered the impact of recorded SUA test results on the likelihood of GP gout diagnoses, with the Gout Calculator as reference.
Methods: The observational study consisted of an analysis of all SUA test results as observed in the electronic medical records of patients with gout diagnosed by Dutch GPs. De-identified data of 87 general practices (east Netherlands) were therefore obtained from the Radboud Technology Center Health Data of the Radboud University Medical Center Nijmegen. Patients with a first International Classification of Primary Care (ICPC) code for gout (T92) as recorded by the GPs between 1-1-2013 and 1-1-2022 were included. Outcomes were proportions of patients with a SUA test result, timely or not timely recorded with respect to the moment of diagnosis. ‘Timely recording’ was arbitrarily defined (30 days before to 30 days after the GP diagnosis). To analyse the impact of a timely recorded SUA level >0.35 mmmol/L we assessed for each patient the likelihood of the GP diagnosis according to the Gout Calculator, given the collected data, and presuming MTP1 involvement in each patient.
Findings: We included 7,782 patients (68.8% male; mean age 64 yrs). Of them 57.0% had at least one SUA level recorded, whereas 43.0% had none. The proportion without a SUA test result varied in the participating practices (17.6 to 98.7%, median 41.9%). A SUA level >0.35mmol/L and timely with respect to establish a gout diagnosis, was seen in 25.9%. Of them 95.6% got a diagnosis ‘gout very likely’ according to the Gout Calculator. A likelihood of a ‘questionable or indeterminate gout diagnose’ or ‘arthritis diagnosis other than gout’ was seen in 74.1% of the patients. All these patients (except 88 women, 1.1%) lacked a timely recorded SUA level >0.35mmol/L. Proportions of patients with timely SUA levels >0.35mmol/L did not change after the 2017 update of the Dutch GP guideline on gout, which incorporates the Gout Calculator. [4]
Conclusion: We found a high proportion of patients with a gout diagnosis by GPs, whose SUA had not been tested for diagnostic reasons. Only a quarter of patients got a SUA test confirming the diagnosis with the Gout Calculator as reference. Ignorance about the SUA level at the gout diagnosis moment implies unnecessary and unwanted diagnostic uncertainty. Moreover, it could have consequences when a patient is unjustly managed as having gout, while there is a risk of an arthritis other than gout.
We advise GPs to be aware of the importance of SUA testing when diagnosing gout. In addition, SUA tested primarily for diagnostic reasons is also useful as baseline measurement recommended to follow up the effect of urate lowering treatment, if indicated.[4]
References:
1. Taylor WJ, Fransen J, Dalbeth N, et. al. Performance of classification criteria for gout in early and established disease. Ann Rheum Dis. 2016 Jan;75(1):178-82.
2. Janssens HJ, Fransen J, van de Lisdonk EH, et al. A diagnostic rule for acute gouty arthritis in primary care without joint fluid analysis. Arch Intern Med 2010; 170: 1120–26.
3. ‘Gout Calculator’ as app in App Store (“gout diagnosis”) and in Google Play (“gout calculator”); Acute Gout Diagnosis Rule available from: https://www.mdcalc.com/calc/2175/acute-gout-diagnosis-rule.
4. Arthritis guideline of the Dutch College of General Practitioners (including gout) 2017. Available from: https://richtlijnen.nhg.org/standaarden/artritis.