Comorbidity of diabetes

1 in 5 (4.9 million) Australians were estimated to be living with multimorbidity in 2017–18 (ABS 2019).

What are multimorbidity and comorbidity?

The terms multimorbidity and comorbidity are often used interchangeably within chronic condition and health-care reporting.

Comorbidity is defined as the occurrence of more than one condition or disorder concurrently. Possible combinations can consist of both physical conditions and/or mental disorders. Whereas multimorbidity is the presence of 2 or more chronic conditions in a person at the same time. These concepts are important for the way different parts of the health system view patients. The concept of comorbidity is useful for the secondary and tertiary-care settings, for example, an endocrinologist might treat a patient with type 2 diabetes as having comorbidity with other diseases. Multimorbidity is a more useful concept in the primary care setting where holistic care is provided that is not determined by the presence of any specific condition (Harrison et al. 2021).

The health effect of multimorbidity can be greater than the combined effect of individual conditions, leading to more severe illness, a poorer prognosis and premature death. People living with multimorbidity generally use more health services, including increased contact with primary health care services, with more complex hospitalisations and poorer outcomes than those living with a single condition.

How many people are living with diabetes, chronic kidney disease and heart, stroke and vascular disease?

Reliable estimates of the comorbidity of diabetes, chronic kidney disease (CKD) and heart, stroke and vascular disease (HSVD) in the Australian population can be derived from large-scale biomedical health surveys. The most recent of these was the National Health Measures Survey, the biomedical component of the 2011–12 Australian Health Survey (ABS 2013).

In 2011–12, an estimated 2.8 million Australian adults (18%) were living with diabetes, CKD and/or HSVD. Of these, 860,000 had diabetes, of which:

  • 480,000 (3.1% of adults) had diabetes only
  • 201,000 (1.3% of adults) had diabetes and CKD
  • 103,000 (0.7% of adults) had diabetes and HSVD
  • 76,700 (0.5% of adults) had diabetes, CKD and HSVD (Figure 1).

Men were more likely than women to be living with all 3 conditions (0.7% compared with 0.3%).

The prevalence of comorbidity of diabetes with CKD and/or HSVD increased with age, from 2.5% of adults aged 55–64 to 9.0% of adults aged 65 and over.

Figure 1: Prevalence of diabetes, CKD and HSVD, and their comorbidity, persons aged 18 and over, 2011–12

The Venn diagram shows the overlapping proportion of adults who had diabetes, chronic kidney disease or heart, stroke and vascular disease in 2011–12. Among adults with these conditions, an estimated 17% had diabetes only and 2.7% were living with all 3 conditions.

Hospitalisations with diabetes, chronic kidney disease and cardiovascular disease

Hospital comorbidity

Where a person has 2 or more of CKD, CVD or diabetes recorded in their episode of hospitalisation, this is referred to as comorbidity. Dialysis hospitalisations have been excluded because they are often performed as routine treatments on a same-day basis and have no other comorbid diagnoses recorded. Note also, the coding rule for diabetes – if present, diabetes is universally coded on a person’s hospital record. This is unlike CVD and CKD, which are coded only if they affected the care and treatment provided during the hospitalisation. This may under-report hospital comorbidity of these diseases.

In 2019–20, there were around 2.1 million hospitalisations in people aged 18 or over in which diabetes, CKD or CVD was present as the principal and/or an additional diagnosis. This equates to 23% of all non-dialysis hospitalisations for people 18 and older.

Of these, nearly 1.2 million included a diabetes diagnosis and over one-third included a diagnosis for CKD and/or CVD. The most common comorbidity including diabetes was CVD and diabetes (169,700, or 8.2%), with diabetes and CKD present in 135,100 hospitalisations (6.5%). There were a further 105,500 hospitalisations (5.1%) where all 3 conditions were present (Figure 2).

Figure 2: Hospitalisations with diabetes, CKD (excluding dialysis) or CVD, persons aged 18 and over, 2019–20

The Venn diagram shows the overlapping proportion of hospitalisations among adults in 2019–20 with diabetes, chronic kidney disease or cardiovascular disease as the principal and/or additional diagnosis. Among the hospitalisations for these conditions 36% were for diabetes only, and 5.1% of hospitalisations were for all 3 conditions.

Variation by age and sex

The rate of hospitalisations with comorbidity of CKD, CVD and/or diabetes increases with age.

In 2019–20, for example, people aged 45–64 were 7.9 times as likely to have a combination of diabetes and CVD recorded on their hospital record as people aged 18–44 (660 and 83 per 100,000 population, respectively). For those aged 65 and over, this difference increased to 35 times the rate of those aged 18–44 (2,900 and 83 per 100,000 population, respectively).

Men were more likely to be hospitalised with comorbidity than women. After adjusting for age, the rate of hospitalisation where all 3 conditions were recorded was 1.7 times as high for men as for women.

Hospital comorbidity in the Aboriginal and Torres Strait Islander population

In 2019–20, there were 89,500 non-dialysis hospitalisations of Indigenous people aged 18 and over where CKD, CVD or diabetes was present as a principal and/or additional diagnoses.

Of these hospitalisations, 32,700 (37%) recorded 2 or 3 of the conditions – 7,700 (8.7%) recorded diabetes and CVD together, 1,700 (1.8%) recorded CVD and CKD, 14,800 (16%) recorded CKD and diabetes, and 8,600 (9.6%) recorded all 3 conditions.

A higher proportion of Indigenous adults had CKD, CVD and diabetes hospital comorbidity, compared with non-Indigenous adults (37% and 22%, respectively). The proportion of Indigenous hospitalisations with all 3 conditions (9.6%) was also higher than that in the non-Indigenous population (5.0%).

After adjusting for age differences in the populations, the rate of hospitalisation of Indigenous people recording all 3 conditions was 5.8 times as high as the rate of non-Indigenous people.

Deaths from diabetes, chronic kidney disease and cardiovascular disease

Often, more than one disease or condition contributes to a death. Along with the underlying cause of death, a medical practitioner or coroner will also record associated causes on a death certificate. The most complete representation of cause-of-death will consider the contribution of both underlying and associated causes (Harding et al. 2014).

Whereas CVD is a common underlying cause of death, diabetes and CKD are more likely to be recorded as associated causes of death. Both diabetes and CKD are known to be under-reported in national mortality statistics and can be omitted from death certificates as contributory causes of death (Sypek et al. 2018, McEwen et al. 2011).

Association of diabetes, CKD and CVD

Of the 159,700 deaths registered among persons aged 18 and over in Australia in 2020, diabetes, CKD and CVD were listed as underlying or associated causes in 90,800 of these. Diabetes was found as an underlying or associated cause in 17,500 cases, with 84% having CVD and/or CKD also recorded on the death certificate. Of those associated with diabetes:

  • 10,100 had diabetes and CVD
  • 780 had diabetes and CKD
  • 3,800 had all 3 conditions recorded.

Figure 3: Deaths with diabetes, CKD and CVD listed as any cause of death, persons aged 18 and over, 2020

The Venn diagram shows the proportion of deaths among adults in 2020 with diabetes, chronic kidney disease or cardiovascular disease as any cause of death. Among deaths from these conditions, diabetes was recorded as the only cause in 3.0% of deaths, and all 3 diseases were recorded as the underlying or associated cause in 4.2% of deaths.