Summary of results
Many patients with sick-leave certificate diagnoses of adjustment and anxiety disorders had ongoing depression. The diagnostic criteria for depression were fulfilled by 76% of patients with a sick-leave diagnosis of adjustment disorder, 67% with a sick-leave diagnosis of anxiety, and 65% with a sick-leave diagnosis of depression. Sick-leave certificate diagnoses of anxiety disorders seemed to be associated with diagnoses of anxiety disorders made in the structured psychiatric interviews (M.I.N.I). There was no significant difference in net sick-leave days between people with sick-leave certificate diagnoses of adjustment disorder, anxiety, or depression. Depression diagnoses made in the structured psychiatric interviews were associated with shorter net sick leave than adjustment disorder diagnoses made in the interviews. High scores on either the MADRS-S or the KEDS symptom severity scale were associated with longer net sick leave.
Comparison of current study results with those of previous studies
The overlapping, dynamic, and sometimes chronic nature (12, 17, 32, 45-48) of common mental disorders seen in primary care patients may underlie several of the findings of the current study. Comorbidity could help explain why depression was found in so many patients on sick leave for adjustment and anxiety disorders. It could also help explain why previous depression, recurrent depression, and generalized anxiety disorder were found in similar levels in all three groups (those with sick leave certification for adjustment disorder, anxiety disorder, or depression).
The dynamic nature of common mental disorders may also have contributed to the relatively low number of patients on sick leave for depression who had ongoing depression according to the structured interview. Perhaps some patients had recovered from their depression by the time of the structured interview, which took place 14 days to 3 months after patients received sick leave certificates. The delay between sick-leave certification and the interviews may also help explain why large numbers of the patients on sick leave for adjustment and anxiety disorders had ongoing depression according to the interview. Patients on sick leave for these disorders might have developed depression during the interval between certification and the structured psychiatric interview. Sick leave itself is a risk factor for depression (2, 15), especially in people with anxiety disorders (2, 8, 17). Burnout also predicts depressive symptoms (49).
The infrequent use of structured psychiatric interviews for mental disorders in primary care (18, 19, 21, 47, 50) could also help explain the differences we observed between the diagnoses on sick leave certificates and the diagnoses made in the structured interviews. A previous review found that clinical assessment alone detects approximately half of all cases of depression, a number that rises to 90% when a structured psychiatric interview (M.I.N.I.) is added to the diagnostic procedure (21, 51). A study in primary care has found that in the absence of a structured psychiatric interview, some mental disorders (e.g., bulimia, obsessive-compulsive disorder) can go undetected or be mistaken for other disorders with similar clinical presentations (51).
Although diagnoses on sick leave certificates are supposed to guide the length and degree of sick leave, we found no association between the two. We found, however, that the diagnoses made in the structured psychiatric interviews were associated with the length and degree of sick leave. Patients who fulfilled the M.I.N.I. criteria for ongoing depression had significantly fewer net sick leave days than those who did not. Additionally, few patients in either region in the current study had sick-leave certificate diagnoses of anxiety disorders, which suggests that the GPs were following recommendations that short and preferably no sick leave should be given to patients with anxiety disorders (52). Finally, the structured psychiatric interviews showed that people with adjustment disorder had the longest sick leave. This is in accordance with Swedish recommendations, which state that long sick leave may be necessary for these patients (52).
More severely ill patients received longer sick leave, which is in keeping with national guidelines (52). In all groups, participants who scored high on KEDS and/or MADRS-S had longer net sick leave than those who had low scores on these instruments. The same pattern has been found in previous studies (1, 16, 29, 34, 35, 53), which suggests that symptom severity may be the factor with the greatest influence on length of sick leave.
Limitations and strengths
This study had a number of limitations. One was that differences in recruitment in the regions of Stockholm and Västra Götaland led to study populations that differed in age, educational level, and treatment with antidepressants. In Stockholm, participants were recruited primarily via invitations from the Swedish Social Insurance Agency. Approximately 10% of those contacted by letter responded that they were interested in participating, which means that this was a highly self-selected group. Additional participants were recruited via advertisements in the press, which may have resulted in another highly self-selected group. In the region of Västra Götaland, rehabilitation coordinators at primary health care centers asked patients who were on sick leave to participate in the study; 21% agreed to participate, and these people may also have differed from those who declined to participate.
A further limitation was the delay between the sick leave diagnoses and the structured psychiatric interviews. As noted previously, common mental disorders seem to overlap and affect one another over time (1, 3, 29, 32, 45-47, 54). It is possible that our results would have differed if all the structured psychiatric interviews had been conducted as part of or immediately after the sick-leave certificate diagnosis.
Finally, our study did not measure self-rated anxiety symptoms, which means that we were not able to compare anxiety symptoms in our study population with length of sick leave. In at least one other study, symptoms of anxiety were the most important predictor of length of sick leave (29).
A strength of this study was that the assessments with structured psychiatric interviews and symptom severity scales were performed by assessors other than the clinicians who performed the sick leave certification. This may have diminished assessment bias. Additionally, the study population was drawn from two regions of Sweden and included both rural and urban areas and areas of varying socioeconomic status, which could increase generalizability.