Chronic Kidney Disease in Tasmania: Protocol for a Data Linkage Study

Creating an interactive map visualising the geographic variations of the burden of diabetes to inform policymaking: An example from a cohort study in Tasmania, Australia

OBJECTIVES

To visualise the geographic variations of diabetes burden and identify areas where targeted interventions are needed.

METHODS

Using diagnostic criteria supported by hospital codes, 51,324 people with diabetes were identified from a population-based dataset during 2004-2017 in Tasmania, Australia. An interactive map visualising geographic distribution of diabetes prevalence, mortality rates, and healthcare costs in people with diabetes was generated. The cluster and outlier analysis was performed based on statistical area level 2 (SA2) to identify areas with high (hot spot) and low (cold spot) diabetes burden.

RESULTS

There were geographic variations in diabetes burden across Tasmania, with highest age-adjusted prevalence (6.1%), excess cost ($2627), and annual costs per person ($5982) in the West and Northwest. Among 98 SA2 areas, 16 hot spots and 25 cold spots for annual costs, and 10 hot spots and 10 cold spots for diabetes prevalence were identified (p<0.05). 15/16 (94%) and 6/10 (60%) hot spots identified were in the West and Northwest.

CONCLUSIONS

We have developed a method to graphically display important diabetes outcomes for different geographical areas.

IMPLICATIONS FOR PUBLIC HEALTH

The method presented in our study could be applied to any other diseases, regions, and countries where appropriate data are available to identify areas where interventions are needed to improve diabetes outcomes.

Island medicine longitudinal cohort study: Rapid rise in chronic kidney disease in rural and remote communities

AIM

To determine the change in incidence and prevalence of chronic kidney disease (CKD) in rural and remote communities over the last decade.

METHODS

We examined the change in age-standardized incidence and prevalence in Tasmania between 2010 and 2020, using a linked dataset that included any adult with a creatinine test taken in a community laboratory during the study period (n = 581 513; 87.8% of the state's adult population). We defined CKD as two measures of eGFR <60 mL/min per 1.73 m2, at least 3 months apart.

RESULTS

State-wide age-standardized prevalence of CKD increased by 28% in the decade to 2020, from 516 to 659 per 10 000 population. Prevalence in men increased 31.3% and women 24.8%. The greatest increase in age-standardized prevalence was seen in rural or remote communities with an increase of 36.6% overall, but with considerable variation by community (range + 0.4% to +88.3%). The increase in the actual number of people with CKD in the decade to 2020 was 67%, with the number of women increasing by 58% and men by 79%.

CONCLUSION

The age-standardized prevalence of CKD in rural and remote regions has increased considerably over the past decade, likely compounded by limited access to primary and secondary healthcare. These findings highlight the need to ensure healthcare resources are directed to areas of greatest need.

The kidney failure risk equation predicts kidney failure: Validation in an Australian cohort

AIMS

Predicting progression to kidney failure for patients with chronic kidney disease is essential for patient and clinicians' management decisions, patient prognosis, and service planning. The Tangri et al Kidney Failure Risk Equation (KFRE) was developed to predict the outcome of kidney failure. The KFRE has not been independently validated in an Australian Cohort.

METHODS

Using data linkage of the Tasmanian Chronic Kidney Disease study (CKD.TASlink) and the Australia and New Zealand Dialysis and Transplant Registry (ANZDATA), we externally validated the KFRE. We validated the 4, 6, and 8-variable KFRE at both 2 and 5 years. We assessed model fit (goodness of fit), discrimination (Harell's C statistic), and calibration (observed vs predicted survival).

RESULTS

There were 18 170 in the cohort with 12 861 participants with 2 years and 8182 with 5 years outcomes. Of these 2607 people died and 285 progressed to kidney replacement therapy. The KFRE has excellent discrimination with C statistics of 0.96-0.98 at 2 years and 0.95-0.96 at 5 years. The calibration was adequate with well-performing Brier scores (0.004-0.01 at 2 years, 0.01-0.03 at 5 years) however the calibration curves, whilst adequate, indicate that predicted outcomes are systematically worse than observed.

CONCLUSION

This external validation study demonstrates the KFRE performs well in an Australian population and can be used by clinicians and service planners for individualised risk prediction.

Costs of major complications in people with and without diabetes in Tasmania, Australia

Objective We set out to estimate healthcare costs of diabetes complications in the year of first occurrence and the second year, and to quantify the incremental costs of diabetes versus non-diabetes related to each complication. Methods In this cohort study, people with diabetes (n  = 45 378) and their age/sex propensity score matched controls (n  = 90 756) were identified from a linked dataset in Tasmania, Australia between 2004 and 2017. Direct costs (including hospital, emergency room visits and pathology costs) were calculated from the healthcare system perspective and expressed in 2020 Australian dollars. The average-per-patient costs and the incremental costs in people with diabetes were calculated for each complication. Results First-year costs when the complications occurred were: dialysis $78 152 (95% CI 71 095, 85 858), lower extremity amputations $63 575 (58 290, 68 688), kidney transplant $48 487 (33 862, 68 283), non-fatal myocardial infarction $30 827 (29 558, 32 197), foot ulcer/gangrene $29 803 (27 183, 32 675), ischaemic heart disease $29 160 (26 962, 31 457), non-fatal stroke $27 782 (26 285, 29 354), heart failure $27 379 (25 968, 28 966), kidney failure $24 904 (19 799, 32 557), angina pectoris $18 430 (17 147, 19 791), neuropathy $15 637 (14 265, 17 108), nephropathy $15 133 (12 285, 18 595), retinopathy $14 775 (11 798, 19 199), transient ischaemic attack $13 905 (12 529, 15 536), vitreous hemorrhage $13 405 (10 241, 17 321), and blindness/low vision $12 941 (8164, 19 080). The second-year costs ranged from 16% (ischaemic heart disease) to 74% (dialysis) of first-year costs. Complication costs were 109-275% higher than in people without diabetes. Conclusions Diabetes complications are costly, and the costs are higher in people with diabetes than without diabetes. Our results can be used to populate diabetes simulation models and will support policy analyses to reduce the burden of diabetes.

Incremental healthcare expenditure attributable to diabetes mellitus: A cost of illness study in Tasmania, Australia

AIMS

To quantify the incremental direct medical costs in people with diabetes from the healthcare system perspective; and to identify trends in the incremental costs.

METHODS

This was a matched retrospective cohort study based on a linked data set developed for investigating chronic kidney disease in Tasmania, Australia. Using propensity score matching, 51,324 people with diabetes were matched on age, sex and residential area with 102,648 people without diabetes. Direct medical costs (Australian dollars 2020-2021) due to hospitalisation, Emergency Department visits and pathology tests were included. The incremental costs and cost ratios between mean annual costs of people with diabetes and their controls were calculated.

RESULTS

On average, people with diabetes had healthcare costs that were almost double their controls ($2427 [95% CI 2322-2543]; ratio 1.87 [95% CI 1.85-1.91]; pooled from 2007-2017). While in the first year of follow-up, the costs of a person with diabetes were $1643 (95% CI 1489-1806); ratio 1.83 (95% CI 1.76-1.92) more than their control, this increased to $2480 (95% CI 2265-2680); ratio 1.69 (95% CI 1.62-1.77) in the final year. Although the incremental costs were higher in older age groups (e.g., ≥70: $2498 [95% CI 2265-2754]; 40-49: $2117 [95% CI 1887-2384]), the cost ratios were higher in younger age groups (≥70: 1.52 [95% CI 1.48-1.56]; 40-49: 2.37 [95% CI 2.25-2.61]).

CONCLUSIONS

Given the increasing burden that diabetes imposes, our findings will support policymakers in future planning for diabetes and enable targeting sub-groups with higher long-term costs for possible cost savings for the Tasmanian healthcare system.

Competing risks of death and kidney failure in a cohort of Australian adults with severe chronic kidney disease

OBJECTIVES

To examine the competing risks of death (any cause) and of kidney failure in a cohort of Australian adults with severe chronic kidney disease.

DESIGN

Population-based cohort study; analysis of linked data from the Tasmanian Chronic Kidney Disease study (CKD.TASlink), 1 January 2004 - 31 December 2017.

PARTICIPANTS

All adults in Tasmania with incident stage 4 chronic kidney disease (estimated glomerular filtration rate [eGFR], 15-29 mL/min/1.73 m² ).

MAIN OUTCOME MEASURES

Death or kidney failure (defined as eGFR below 10 mL/min/1.73 m² or initiation of dialysis or kidney transplantation) within five years of diagnosis of stage 4 chronic kidney disease.

RESULTS

We included data for 6825 adults with incident stage 4 chronic kidney disease (mean age, 79.3 years; SD, 11.1 years), including 3816 women (55.9%). The risk of death increased with age - under 65 years: 0.18 (95% CI, 0.15-0.22); 65-74 years: 0.39 (95% CI, 0.36-0.42); 75-84 years, 0.56 (95% CI, 0.54-0.58); 85 years or older: 0.78 (95% CI, 0.77-0.80) - while that of kidney failure declined - under 65 years: 0.39 (95% CI, 0.35-0.43); 65-74 years: 0.12 (95% CI, 0.10-0.14); 75-84 years: 0.05 (95% CI, 0.04-0.06); 85 years or older: 0.01 (95% CI, 0.01-0.02). The risk of kidney failure was greater for people with macroalbuminuria and those whose albumin status had not recently been assessed. The risks of kidney failure and death were greater for men than women in all age groups (except similar risks of death for men and women under 65 years of age).

CONCLUSIONS

For older Australians with incident stage 4 chronic kidney disease, the risk of death is higher than that of kidney failure, and the latter risk declines with age. Clinical guidelines should recognise these competing risks and include recommendations about holistic supportive care, not just on preparation for dialysis or transplantation.

Island medicine: using data linkage to establish the kidney health of the population of Tasmania, Australia

Objective

To report (using linked laboratory data) the incidence, prevalence and geographic variation of chronic kidney disease (CKD) across the whole island population of Tasmania, Australia.

Methods

A retrospective cohort study (the Tasmanian Chronic Kidney Disease study (CKD.TASlink)) using linked data from five health and two pathology datasets from the island state of Tasmania, Australia between 1/1/2004 and 31/12/2017. We used data on 460,737 Tasmanian adults (aged 18 years and older, representing 86.8% of the state's population) who had a serum creatinine measured during the study period. We defined CKD as per Kidney Disease Outcomes Quality Initiative, requiring two measures of estimated glomerular filtration rate (eGFR) <60 mL/min/1.73m², at least three months apart. Kidney replacement therapy (KRT) included dialysis or kidney transplantation.

Results

We identified 56,438 Tasmanians with CKD during the study period, equating to an age-standardised annual incidence of 1.0% and a prevalence of 6.5%. These figures were higher in women, older Tasmanians and people living in the North-West region of Tasmania. Testing for urinary albumin:creatinine ratio is increasing, with 28.5% of women and 30.8% of men with stage 3 CKD having both an eGFR and uACR in 2017. Use of KRT was consistently seen in >65% of Tasmanians with eGFR <15 mL/min/1.73m².

Conclusion

There is geographic and gender variation in the incidence and prevalence of CKD, but it is reassuring to see that the majority of people with end-stage kidney failure are actually receiving treatment with dialysis or transplantation.