Our study results show a generally high health care utilisation with more than 15 practice contacts and three to four referrals on the average per year. Consistent with previous reports, we found that high medical service utilization is associated with prevalent mental disorder. Beyond that, our findings indicate that the influence of psychosomatic disorders on utilisation appears to be stronger than the influence of purely somatic disorders.
The impact of psychosomatic or mental disorders on health care utilisation is already well described for gate keeping systems [5, 6]. We found such an effect also in our survey. However, in our study high utilisation was defined when patients were coming more than eleven times per year into practice, which is more than twice as much compared with an US study . Beyond that, we confirmed a very high rate of practice contacts per year in general which is twice as high as in the US or the Netherlands . These facts might be due to free access of health care and the rewarding system. In Germany a physician receives reimbursement per quarter only if the patient comes within the respective quarter. A previous German survey [3, 4] found only 3.8 practice visits of patients with and 2.7 visits of patients without mental disorders; and they found only 12.9 days of disability. However, the information about health care utilisation in that survey was assessed by self-rating which might have led to distorted estimation, whereas our information was gathered by review of the computerised charts. Detailed analyses of our study demonstrated that especially permanent mental disorders were leading to high practice contact rates, referrals and periods of disability. The impact of psychosomatic diagnoses was stronger than that of permanent somatic diagnoses in general with exception for referrals. These results illustrate that the coding of permanent mental disorders might allow identifying patients at risk for high utilisation during medical encounter. Identification of difficult patients is valuable not only regarding resource use but in particular as high utilisation is associated with harmful side effects [16, 17]. However, our findings highlight that the management of patients with psychosomatic or mental problems is a big challenge in German general practices. On the one hand, these patients are frequent attenders. On the other hand, it seems likely that there is not enough time for them due to the high contact rate. Therefore, structural changes in the health care reimbursement systems might be necessary to give physicians more time to actively detect and manage patients with mental problems. This might be useful as several patient-centred communication strategies have been shown to improve the management of patients with high psychosomatic co-morbidity, like the intervention of an extended reattribution and management for patients with functional disorders in general practice [8, 18].
The documentation of permanent diagnoses has a crucial role in the German health care system as it is the precondition for payment of specific diagnostic and therapeutic procedures. This role will become even more relevant in future as insurances have to invest more in sicker patients. It is assumed by health care managers that the morbidity is adequately reflected by ICD-10 diagnoses which are coded in general practices. Therefore, practitioners will have to document each reason of encounter as an ICD-10 diagnosis for each quarter. However, the concept of ICD-10-documentation is not without drawbacks. In primary care it is often impossible to establish a diagnosis for each reason of encounter. Beside that, practitioners might be tempted to document questionable diagnoses for ensuring their salary. Furthermore, our findings suggest that the mental diagnoses have a more profound impact on practice visits and periods of disability than the somatic diagnoses. This was especially true for the periods of disability which were not even significantly associated with the number of somatic diagnoses. This might underline that exaggerated coding of diagnoses does not necessarily lead to a comprehensive understanding of the patients' condition and the associated resource use on practice level. In fact, such coding might lead to distorted estimation of resource use.
The reliability of the permanent diagnoses has to be discussed as a limitation. It is unlikely that the mental diagnoses have been made exactly according to the ICD-10 classification. The related diagnostic algorithms are complex and might be not always suitable for primary care [19, 20]. Patients with coded mental diagnoses scored significantly higher in all PHQ scales relating to depression, anxiety, panic and somatoform disorder indeed. It might be a limitation that coded diagnoses may contain past diagnoses that the patient is not suffering from now. However the clear differences of the PHQ scales suggest that the coded diagnoses might have been updated in some degree. For example, patients with mental disorders showed PHQ values representing at least moderate depression . Adding the PHQ anxiety and panic items to a summary score is not commonly used. The GAD-7 was shown to be suitable for continuous measurement , but this questionnaire was not available to us when the study was established. However, the scales are similar; and the sum of the PHQ items would be lower than the GAD-7 items. This would even have led to an underestimation of the anxiety and panic scores. The validity of the permanent somatic ICD-10-diagnoses might be questioned as other coding systems like ICPC-2 (International Classification of Primary Care) are supposed to be more valid for research purposes in primary care [22, 23]. However, there is also conflicting evidence regarding the diagnostic precision of ICPC-2 . Nonresponder were significantly older than responder. This might lead to an underestimation of the frequency of practice contact, referrals and periods of disability. However, it is unlikely that this affects our findings on the role of psychosomatic comorbidity.