Using prednisolone and cortisol assays to assess adherence in oral corticosteroid dependant asthma: an analysis of test-retest repeatability

John Busby, Cécile T Holweg, Akiko Chai, Peter Bradding, Rekha Chaudhuri, Adel H Mansur, John G. Matthews, Andrew Menzies-Gow, James Lordan, Liam Heaney

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Background and objective: Non-adherence is an important issue within severe asthma. Prednisolone and cortisol assays have been proposed as an inexpensive, objective measure of adherence for oral corticosteroid (OCS)-dependent asthmatics, however, little is known about the reliability of these tests. Methods: 41 severe OCS-dependent asthmatics had their prednisolone and cortisol measured during six study visits over a three month time period. Subjects were classed as non-adherent/variably-adherent if they had undetectable prednisolone and/or cortisol >100 nmol/L. Intraclass correlation coefficients (ICCs) were used to assess the test-retest reliability of prednisolone and cortisol, and Gwets AC1 kappa was used to assess the reliability of the adherence classification. Mean change in blood eosinophils for adherent and variably/non-adherent visits were calculated and linear regression with cluster-robust standard errors was used to test for differences. Results: 30 subjects were included in the analysis. Reliability was poor for prednisolone (ICC: 0.43; 95% CI: 0.27, 0.59), and moderate for cortisol (ICC: 0.60; 95% CI: 0.44, 0.74). Using the combined rule, subjects were classified as adherent during 141 (88%) visits, with 21 subjects (70%) adherent during all study visits. The adherence classification had almost perfect reliability (Kappa: 0.84; 95% CI: 0.74, 0.95). Blood eosinophils were decreased by 47 cells/µl (95% CI: 11, 84) during adherent visits but increased by 65 cells/µl (95% CI: -4, 134; Pdifference=0.03) during variably/non-adherent visits. Conclusions: Assessing adherence to maintenance OCS using a simple rule based on prednisolone and cortisol assays is highly reliable and correlated with blood eosinophil changes. Clinicians should have confidence in the results of this rule.
Original languageEnglish
Article number101951
JournalPulmonary Pharmacology and Therapeutics
Early online date13 Sep 2020
Publication statusPublished - Oct 2020


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