Medication non-adherence is a major public health issue associated with poor clinical and economic outcomes. Medication adherence should be regarded as the fifth vital sign, making adequate measurement crucial.

The Basel Assessment of Adherence to Immunosuppressive Medication Scale (BAASIS©) was developed to assess adherence to immunosuppressive drugs in adult and adolescent transplant recipients. The BAASIS© can also be easily adapted to assess medication adherence in other populations of chronically ill patients.

The BAASIS^© follows the ABC taxonomy of medication adherence (Vrijens et al., 2012) which defines adherence as «the process by which patients take their medication as prescribed». This taxonomy identifies three quantifiable phases of adherence: initiation, implementation, and persistence. The BAASIS© assesses all three phases.

The BAASIS© is available in both interview and written self-report formats in various languages.

An explanation of the BAASIS^© can be found here.

The validity of the BAASIS© has been analyzed psychometrically in a meta-analysis of individual patient data (Denhaerynck et al., 2023; commentary: Elias et al., 2023).
Predictive validity has been established for critical outcomes such as biopsy-proven graft rejection (Haupenthal et al., 2025).

Denhaerynck K, Dobbels F, Košťálová B, De Geest S; BAASIS consortium. Psychometric Properties of the BAASIS: A Meta-analysis of Individual Participant Data [published online ahead of print, 2023 Mar 23]. Transplantation. 2023;10.1097/TP.0000000000004574. doi:10.1097/TP.0000000000004574

Elias C, Cherukuri A. BAASIS for Monitoring Therapy Nonadherence in Clinical Transplantation: Are We There Yet? [published online ahead of print, 2023 Mar 23]. Transplantation. 2023;10.1097/TP.0000000000004575. doi:10.1097/TP.0000000000004575

Haupenthal F, Doberer K, Kapps S, Kläger J, Bauernfeind F, Denhaerynck K, Kainz A, De Geest S, Bond G. Self-reported Non-adherence to Immunosuppressive Medication Detected by the BAASIS Predicts Allograft Rejections in Kidney Transplant Recipients. Nephrol Dial Transplant. 2025 Apr 28:gfaf078. doi:10.1093/ndt/gfaf078. Epub ahead of print. PMID: 40295140.

Vrijens B, De Geest S, Hughes D, Kardas P, Demonceau J, Ruppar T, Dobbels F, Fargher E, Morrison V, Lewek P, Matyjaszczyk M, Mshelia C, Clyne W, Aronson JK, Urquhart J for the ABC project team. A new taxonomy for describing and defining adherence to medications. British Journal of Clinical Pharmacology 2012; 691-705. doi:10.1111/j.1365-2125.2012.04167.x