A readily available urine test could identify ulcerative colitis (UC) patients who are non-adherent to their mesalamine therapy, research shows.
"This study demonstrates that measuring urine salicylate levels, by the standard colorimetry test used to measure blood salicylate levels, provides a reliable marker of recent mesalamine ingestion," say Alan Moss (Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA) and colleagues.
The study, reported in the American Journal of Gastroenterology, included 93 patients being prescribed mesalamine for UC and 20 control patients.
Levels of 5-aminosalicylic acid (5-ASA) metabolites (5-ASA and n-acetyl-5-ASA) in the urine - the detection of which requires gas or liquid chromatography mass spectrometry - significantly correlated with levels of salicylates as measured by the much simpler colorimetry. This suggests that urinary salicylate levels could be used as a surrogate marker for 5-ASA ingestion, say the authors.
The mean urine salicylate level among controls was 6 mg/dL compared with 60 mg/dL among patients taking mesalamine. The authors determined that a cut-off level of 15 mg/dL could distinguish controls from those who had taken mesalamine, with a sensitivity of 95% and a specificity of 77%.
As reported in previous studies, patients' self-reports of adherence did not correlate well with their biologic measurements. Indeed, when the authors divided patients into low- and high-adherence groups based on their response to the Morisky Medication Adherence Scale-8, there was no significant difference in urine salicylate levels between the two groups.
But, by following the pharmacy refill records of 86 patients during the 6 months after the urine test, the authors showed that the urine test could detect mesalamine non-adherence among these patients. Those with a urine salicylate level below the 15 mg/dL cut-off value were 2.7 times more likely to be poorly adherent according to their pharmacy records (medication possession ratio < 0.8).
Previously, physicians have had difficulty in assessing levels of adherence in the clinic because measurements of biologic markers are costly and hard to access and, as demonstrated in this study, patients' self-reports of adherence often fail to correlate with objective measurements of mesalamine intake.
The authors conclude that the urine salicylate test, which costs around US$ 10-20 (€ 7.50-15), could be used to help physicians identify those patients at risk for relapse, in order to address their adherence to treatment and thus prevent some of the health costs associated with non-adherence.
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