In this study of the 2010 nationwide medical and psychiatric hospital care claims data in the Netherlands, 217,887 individuals (4.4% of total claims) utilized both medical and psychiatric hospital care. Compared with HUPCs, HUMPCs were more often diagnosed with: organic mental disorders behavioral syndromes associated with physiological disturbances and physical factors; mood [affective] disorders; neurotic, stress-related, and somatoform disorders; and disorders of adult personality and behavior. Claims for these HUMPCs accounted for €2.9 billion, equaling 19% of total claims in 2010. Moreover, the medical claims of HUMPCs were 40% higher than claims for HUMCs, and the psychiatric claims for HUMPCs were 10% higher than for HUPCs.
Medical healthcare utilization of psychiatric patients
Medical healthcare utilization differences for psychiatric patients might be related to patient and health system factors . In this subsection we concentrate on our findings with respect to these two (sets of) factors.
In respect of psychiatric patients, risk factors for medical illness and associated healthcare utilization are expected to be related to patient factors, such as socio-economic factors, medical factors such as the presence of severe mental illness (SMI) and comorbid substance use disorder, and other behavioral risk factors such as a lack of physical activity and high body-mass [27, 28]. There was an over-representation of HUMPCs compared to HUPCs within the sub-chapter personality disorders, known for the association with chronic medical conditions such as obesity, pain disorders, syncope, seizures and arthritis [29, 30]. In addition the sub-chapter ‘behavioral syndromes associated with physiological disturbances and physical factors’ was over-represented with respect to HUMPCs. Within this sub-group, for instance, eating disorders were associated with increased risks for serious medical illnesses and premature death .
The presence of mental illness may in some cases reduce somatic care-seeking. For example, people with mental illness may have difficulties engaging in health services, reporting medical problems, and distinguishing physical symptoms from the symptoms of mental illness, especially if health services were non-inclusive or perceived to be non-inclusive . These mechanisms might then lead to reduced healthcare utilization. The finding that psychotic spectrum disorders were under-represented in HUMPCs compared with HUPCs appeared to be compatible with our hypothesis and previous work . For example, patients with anxiety disorders or schizophrenia were less frequently diagnosed with hypertension than the general population. Additionally, patients with schizophrenia less frequently used antihypertensives and lipid-lowering drugs . Swildens et al. showed that Dutch patients with non-affective psychotic disorders were prescribed somatic medication less frequently and experienced lower somatic healthcare utilization .
Health system factors
Differences in healthcare availability and quality might contribute to psychiatric patients’ poor physical health outcome . These differences include an inferior standard of care, the wrongful attribution of medical symptoms to psychiatric conditions (‘diagnostic overshadowing’), and clinicians’ reluctance to provide specific medical procedures due to perceived intolerance to psychological stress, difficulty getting informed consent, compliance issues, or substance misuse [33, 34]. Such mechanisms might have contributed to our finding that disorders of psychological development (including language disorders and speech disorders) were under-represented in HUMPCs.
Health services are often perceived as non-inclusive by people with psychiatric illnesses. Fragmentation of care and social stigma further compromise adequate access to healthcare for these groups [14, 35]. Our data, in all likelihood, reflected the under-representation of patients with schizophrenia and substance use disorders in medical health care since these groups were under-represented in HUMPCs compared to HUPCs.
Inadequate healthcare utilization by psychiatric patients may result in higher claims expenditures of HUMPCs, as shown in our study. These patients have a higher risk for medical illness and experience more extended lengths of hospital stay. Restrictions in accessibility (as described above) and delayed diagnosis and treatment might lead to avoidable ED visits and (re) admissions . LOS and readmissions were considered important cost-drivers of hospital care  and might thus explain many of the excess claims that we found for HUMPs compared to HUPCs and HUMCs.
In contrast, diagnoses of personality disorders and psychotic spectrum disorders were associated with lower psychiatric claims in HUMPCs than HUPCs. Personality disorders are known to pose a high economic burden . Thus, it is remarkable that we found lower median costs of psychiatric claims for HUMPCs than HUPCs in these patient groups. A possible explanation is the lower probability of admission to specialized care for patients with personality disorders found by van Veen et al. . A possible reason for the lower number of psychiatric claims for psychotic spectrum disorders in HUMPCs compared to HUPCs was that these patients tended to avoid healthcare, presenting first in medical hospitals and only when they had developed acute medical symptoms, as found by Swildens et al. . Future research should examine how care can be effectively improved to alleviate this situation.
Public health implications
Our study found that HUMPCs, in almost all subgroups, had increased healthcare costs compared to HUMCs and HUPCs. Because patients with a mental disorder are more likely to have a physical disorder, it is important that physical disorders are detected early. The efforts to improve physical health in mentally ill patients could be to focused on patients with severe mental disorders . Our study shows that a focus on public health is important for all patients with mental health problems. This should take into account, social determinants – the conditions in which people are born, grow up, live, work and age – and unhealthy lifestyles are intertwined and negatively affect the risk for physical and psychiatric disorders . It is important to intervene early in life on social and lifestyle risk factors that significantly reduce the risk of physical and psychiatric illness disorders . In the long run, hospital healthcare utilization may decrease due to these efforts.
In the Netherlands health care insurance is mandatory, thus replication of our results will not easily be accomplished in countries with different accessibility of care. On the other hand, the results will most likely be replicable for citizens with an inclusive health insurance package. A further limitation may be that this nationwide data was 10 years old, but since no major reforms have taken place, it can be assumed that general healthcare utilization patterns were likely to have been stable over time. It is reassuring that our findings are in line with those reported in recent literature. Hence, we consider these results to be representative both currently and for other countries with inclusive health insurance packages. A significant finding was that median claims in specialist medical care were considerably lower than median claims in psychiatric hospital care. This can be explained by a greater emphasis on outpatient care within specialist medical care. Many outpatients’ DBCs have low reimbursement rates, and thus median claims for medical care are lower than for psychiatric hospital care. In this nationwide study, we used POD and POR. Other studies that examined the impact of concurrent medical and psychiatric disorders on health utilization used odds ratios (OR) [9,10,11,12] or latent class analyses [27, 28]. The calculation of the POR is comparable to that of the OR, and our results are therefore comparable to other studies. We only carefully speculated about possible patient and health system mechanisms that may explain the differences in healthcare utilization and claims in this study, however, our data were insufficient to formally examine these interpretations.