Medically certified sickness absence

In the past, doctors and researchers considered absence as a result of sickness to be a (socio)economic and political matter rather than a medical or public health one, so little attention was paid to sickness absence in the general medical literature. Recently, politicians have stressed that reducing work related ill health and sickness absence is a top priority, and sickness absence is increasingly seen as a public health problem in the general medical literature.1 The doctor’s role in sickness certification has been debated because of the tension with doctors also being patient advocates; the extra work caused by certification has also made it unpopular.

The linked prospective cohort study (the Whitehall II study) by Head and colleagues (doi:10.1136/bmj.a1469) finds that the almost 30% of British civil servants who had one or more spells of medically certified sickness absence (>7 days) in 1985-8 had a 66% increased risk of premature death during follow-up compared with those with no medically certified spells.2 Although the relation between sickness absence and mortality has already been described,3 4 their study shows that specific diagnostic information improves the prediction of mortality. In particular, sickness absences resulting from circulatory, surgical, and psychiatric diseases were strongly associated with increased mortality. Surprisingly, sickness absences with a psychiatric diagnosis were predictive of cancer related mortality also. Another cohort study found an association between diagnosis specific sickness absence and mortality.5

To shed light on the relation between sickness absence and mortality we tried to explain the results using a simple approach. As Head and colleagues state, a direct and independent causal association between sickness absence and mortality is unlikely. Instead, health problems are probably related to both sickness absence and to future serious illness and mortality. In line with this explanation, sickness absence can be seen as an early biomedical risk indicator for serious illness and mortality. In addition to this biomedical explanation, evidence exists for a causal relation between work related factors—such as high job demands, work stress, and organisational downsizing—and serious illness and mortality.6 7 8 Work related factors are also independently related to sickness absence—self reported poor psychosocial environment at work predicted medically certified sickness absence.9

Finally, self selection might be inherent in the sick note system itself. Workers without an increased risk for serious illness more often return to work within one week (refrain from requesting medical certificates) than their more unhealthy colleagues—medically certified absence is associated with higher mortality than self certified absence.3 If work related and social security system factors are taken into account, sickness absence is not only an early biomedical, but also an early psychosocial, risk indicator for serious illness and mortality.

Although Head and colleagues’ study is of high quality, it has some limitations. Firstly, although the authors adjusted for the main confounding factors—such as employment grade, age, body mass index, and hypertension—other (unknown) baseline health differences may exist between the groups. Workers without spells of medically certified sickness are generally healthier than those with (long term) sickness absence and work disability. Baseline health differences could therefore have contributed to the differences in mortality. However, if our approach is correct, statistical correction for all baseline health differences would have resulted in erroneous overadjustment and would have attenuated the relation between sickness absence and mortality. Secondly, in line with our simple approach, work related factors could also have played a confounding role. To shed light on the role of such factors, the authors should adjust for them in the future.

What are the implications of the results for clinical practice? Workers’ visits to a general practitioner are often related to sickness absence and work related diseases, but work related factors are rarely identified or managed by general practitioners.10 General practitioners do not feel skilled in work related problems and are uncomfortable with sickness certification. Yet they are the key to improving the medical care of people both in and out of work because of their gatekeeper role in the sick note system and the poor provision of occupational health in most countries, including the United Kingdom.1

Specific diagnostic information on sickness absence may provide general practitioners with a useful biopsychosocial tool to identify groups of workers with an increased risk of serious illness and mortality. With the help of this tool, they could also identify patients with work related health risks and refer them to occupational physicians for targeted work related interventions. Occupational physicians are best equipped to manage these patients,1 and recent studies show that sickness absence as a result of work related physical and mental health problems can be managed effectively.11 12