International classification of functioning, disability and health in the sickness certification process

<p dir="ltr">Background: In Sweden's healthcare system, sickness certification has long been a routine responsibility of general practitioners-yet its complexity continues to challenge patients, clinicians, and policymakers. To improve assessments of work-related disability and address rising sick leave rates, the International Classification of Functioning, Disability and Health (ICF) was introduced into the Swedish sickness certification process in the early 2000s. This thesis aims to examine how the quality of information in sickness certificates has changed over time and to explore whether, and how, the ICF can support improvements of the sickness certification process, with a particular focus on the documentation and assessment of work-related disability due to depression and chronic pain.</p><p dir="ltr">Methods: The thesis comprises four descriptive studies using both quantitative and qualitative methods.</p><p dir="ltr">Study I is a repeated cross-sectional study of 783 sickness certificates issued in primary health care in 2004, 2009 and 2012. A structured, expert-based protocol was used to assess changes in certificate quality. Logistic regression models were applied to examine associations between certificate quality and patient-, sick-leave-, and physician-related factors.</p><p dir="ltr">Studies II and III evaluated the applicability of the ICF and selected ICF Core Sets for coding information on work-related disability in certificates for depression, long-term musculoskeletal pain and fibromyalgia. The qualitative method of ICF linking was used. Study II used a small local sample of sickness certificates (n = 59), while Study III used a large national sample (n = 400).</p><p dir="ltr">Study IV applied the same ICF linking method to analyse the content of the Test Instrument for Profile of Physical Ability (TIPPA), evaluating its relevance in relation to ICF Core Sets for chronic widespread pain.</p><p dir="ltr">Results: Study I showed a statistically significant improvement in the quality of sickness certificates during the eight years. Despite these improvements, the overall quality remained low. Diagnosis and sick leave duration were associated with the quality in 2004/2009, and patient's sex in 2012. The structured method developed for assessing certificate quality has the potential to be useful in future evaluations.</p><p dir="ltr">Study Il revealed that the ICF was suitable for coding 75-83 percent of the information in the sample. However, some relevant categories were missing from the ICF Core Set for disability evaluation in social security, including b130 Energy and drive functions and b134 Sleep functions.</p><p dir="ltr">In Study III, coding to the ICF remained consistent (78-85 percent), and additional relevant but missing categories in the corresponding ICF Core Sets were identified. For the ICF Core Set for depression, these included b455 Exercise tolerance functions and b230 Hearing functions. For the ICF Core Set for chronic widespread pain, missing categories included b144 Memory functions, b770 Gait pattern functions, and b230 Hearing functions.</p><p dir="ltr">Study IV showed that TIPPA effectively captured key physical aspects of functioning, particularly within the activity and participation component. However, psychological domains essential for assessing work ability-such as problem-solving and stress management-were not covered.</p><p dir="ltr">Conclusion: The findings demonstrate an overall improvement in the quality of sickness certificates over the study time, with patient's sex emerging as a factor associated with the quality in the latest sample. The ICF framework proved suitable for capturing work-related disability information in certificates for depression, long-term musculoskeletal pain, and fibromyalgia, covering the majority of relevant concepts. Adjustments to existing ICF Core Sets are recommended to enhance their applicability in sickness certification. While TIPPA assesses physical functioning, it does not fully address psychological domains critical for evaluating work ability in cases of long-term musculoskeletal pain.</p><h3>List of scientific papers</h3><p dir="ltr">I. <b>Fresk M.</b>, Grooten, W., Backlund, L., Arrelöv, B., Skånér, Y., Henriksson, P., Kiessling, A. Quality Assessment in Sickness Certificates - Changes Over an Eight-Year Period in Sweden and Associated Factors. [Manuscript]</p><p dir="ltr">II. <b>Fresk, M.</b>, Grooten, W., Brodin, N., Backlund, L., Arrelöv, B., Skånér, Y., Kiessling, A. (2023). Mapping information regarding the work-related disability of depression and long-term musculoskeletal pain to the International Classification of Functioning, Disability and Health and ICF Core Sets. Frontiers in rehabilitation sciences, 4, 1159208. <a href="https://doi.org/10.3389/fresc.2023.1159208" rel="noreferrer" target="_blank">https://doi.org/10.3389/fresc.2023.1159208<br></a><br></p><p dir="ltr">III. <b>Fresk, M.</b>, Grooten, W., Brodin, N., Backlund, L., Arrelöv, B., Skånér, Y., Kiessling, A. (2024). Exploring international classification of functioning, disability and health applicability for coding work-related disability: a study on depression and fibromyalgia in Swedish sick leave certificates. Journal of rehabilitation medicine, 56, jrm36886. <a href="https://doi.org/10.2340/jrm.v56.36886" rel="noreferrer" target="_blank">https://doi.org/10.2340/jrm.v56.36886<br></a><br></p><p dir="ltr">IV. <b>Fresk, M.</b>, Brodin, N., Grooten, W. J., Joseph, C., Kiessling, A. (2019). Mapping a measure of physical ability for persons with long-term musculoskeletal pain to the ICF and ICF Core Sets. European journal of public health, 29(2), 286-291. <a href="https://doi.org/10.1093/eurpub/cky135" rel="noreferrer" target="_blank">https://doi.org/10.1093/eurpub/cky135</a></p>