Point-of-Care Uric Acid Testing

Uric Acid POC Testing

When we order uric acid tests in the clinic, SU is measured by a uricase-based laboratory assay on plasma samples obtained after venous puncture. For ease of administration, POC testing would have to involve a capillary blood sample, similar to home glucose monitoring. Can it be done?

Believe it or not, uric acid POC testing was invented as early as 2001.⁷ A routine internet search finds a couple different meters available for commercial purchase in the U.S. and abroad. You could buy one on Amazon for about $100. However, a literature search for the evidence to support use yields few studies.

Small studies have demonstrated the reliability and validity of POC testing with the HumaSens^plus meter, with close correlation between capillary uric acid values and venous SU values.⁸ Discrepancies between POC testing and laboratory values that would influence treatment escalation decisions were observed in 9% of patients (for the second generation HumaSens2.0^plus device).⁹ Of note, hematocrit can influence POC uric acid measurements by modifying the blood viscosity of whole blood. Thus, the manufacturer of these meters recommends restricting use to hemoglobin ranges of 10.0 g/dL to 18.3 g/dL. Factors that affect glucose monitoring—like finger temperature, tissue perfusion and acid-base status, apply too.

Glucose meters require a maximum 15% (percent deviation) accuracy compared with the reference method, with 95% of the measurements in the acceptance range, to achieve regulatory approval.¹⁰ So these uric acid POC testing meters would meet the mark.

Potential Benefits

As a rheumatologist, I think the benefits of uric acid POC testing are self-evident. But for the sake of completeness, I discussed the concept with Alan Baer, MD, professor of medicine, Division of Rheumatology, Johns Hopkins University, Baltimore. Dr. Baer is a gout expert and an ACR Master to whom I have looked up since my intern year. He has taken care of people with gout for a long time. And he had never heard of uric acid POC testing.

“Gout is something for which we’ve had effective treatment since the 1960s,” says Dr. Baer. “It’s a shame that gout continues to be treated inadequately. We are so good at preventing erosive joint disease in rheumatoid arthritis, but [we] fail miserably in gout.”

How might uric acid POC testing make a difference? Let us count the ways.

1. Titration of ULT to achieve target SU: With convenient home POC testing, uric acid levels could be checked as often as every two weeks, allowing for rapid titration of ULT to achieve target SU as per ACR guidelines.¹¹
2. Positive feedback to improve adherence to ULT: “Many patients that I see with ‘refractory’ or tophaceous gout tell me they took allopurinol in the past, but continued to have gout flares and thus stopped it due to apparent inefficacy,” says Dr. Baer. “Some tell me that it made their gout worse. I tell them that allopurinol takes time to work, and that lowering the uric acid to levels of less than 6 mg/dL is essential for dissolving the gout crystals in their joints. I also detail the importance of taking colchicine as a prophylactic agent in this setting. POC testing could give such patients positive feedback, allowing them to watch their uric acid levels fall over time.”