End-stage renal disease in Aboriginals in New South Wales: a very different picture to the Northern Territory

The 30 June 1996 estimate of the Indigenous population (386 049) represented 2.1% of the total Australian population,⁴ but Aboriginals constitute 5% of the Australian members of the Australia and New Zealand Dialysis and Transplant Registry (ANZDATA).⁵ Whether the increasing incidence and prevalence of renal disease is occurring in NSW as well as nationally and in the NT has not been well documented.

The aims of our study were to document the number of new Aboriginal patients with ESRD in NSW during 1987 to 1998 and compare recent trends in incidence with national and NT data, and to compare for Aboriginal and non-Aboriginal patients in NSW:

• the patterns of aetiology of ESRD;

• the demographic characteristics at the time of being entered into ANZDATA;

• the outcomes for individuals who were notified to the Registry during the period 1987 to 1998; and

• patient and graft survival for those who received transplants during the period 1987 to 1998.

For NSW, the NT and across Australia, we analysed:

• the number of Aboriginal patients entered into ANZDATA from 1987 to 1998 in NSW, the NT and across Australia; and

• the average annual incidence of ESRD.

For NSW only, we analysed:

• primary renal disease diagnostic category;

• mean age;

• outcome data at 31 March 1998 for people who had been entered into ANZDATA since 1 January 1987. Outcomes were categorised as death, functioning transplant, haemodialysis, continuous ambulatory peritoneal dialysis (CAPD), and loss to follow-up or having moved interstate;

• causes of death, categorised into cardiac, vascular, infection, social, malignancy and other;

• patient survival and graft survival for transplants performed between 1 January 1987 to 31 March 1998.

The average annual incidence of ESRD was calculated using Australian Bureau of Statistics (ABS) estimates and projections of the Aboriginal and Torres Strait Islander population for the years between actual Census counts. These estimates are based upon current trends in fertility and mortality and take into account an increasing propensity for people to identify themselves as being of Indigenous origin. The definition of "Aboriginality" from both data sources (ANZDATA and ABS) relies upon self-identification. Annual incidence was calculated as an average for each two-year period, as there is marked variability in the number of new patients per year, and small absolute numbers.

Statistical analysis of demographic and outcome data was performed using STATA 5.0.¹¹ A t test of means and χ² test or Fisher's exact test of proportions were performed. Survival analysis was performed at the ANZDATA Registry. Data were provided as actuarial life-table estimates and the log rank test was performed. The data were entered into STATA 5.0 and graphed.

Our results show that diabetes, glomerulonephritis and hypertension are the prominent primary causes of ESRD among NSW Aboriginals. The rise in renal failure attributed to diabetes follows a similar pattern to that noted in Aboriginals across Australia.¹⁰ The pattern of primary causes of renal disease is consistent between Aboriginal populations in different States.¹⁰

Impediments to effective and culturally appropriate service delivery to Aboriginal patients have been postulated as reasons for poor survival and high withdrawal rates from treatment.¹² Therapeutic programs have typically removed people from their cultural and social support networks by requiring patients to leave their land, families and communities.¹³ Unlike in the NT, South Australia and Western Australia, there are few remote, non-urbanised communities in NSW; Aboriginals in NSW reside predominantly in cities and rural towns.

The higher proportion of Aboriginal patients with uncertain aetiology of their ESRD is consistent with a lower renal biopsy rate, which may relate to late referral and lack of access to renal specialist services. In NSW, specialist renal services are increasingly being provided where Aboriginals live. The Statistical Local Areas with the highest proportion of Indigenous people are Brewarrina (53.1%), Central Darling (25.3%), Bourke (24.5%) and Walgett (20.4%).¹⁴ CAPD training is now occurring in some larger rural centres, and haemodialysis facilities are provided in Bourke and Brewarrina. These initiatives, which significantly reduce the dislocation of patients from their community and remove impediments to the delivery of appropriate ESRD services, may facilitate improved survival.

There is a tendency towards lower patient survival and graft survival among NSW Aboriginals compared with non-Aboriginals, despite the Aboriginal graft recipients' being younger. In the NT, graft and patient survival among Aboriginals are significantly worse at one and five years than among non-Aboriginals.² A significant difference in survival is not evident in the NSW data. The larger 95% confidence intervals in the NSW Aboriginal group are a consequence of fewer transplants being performed: 36 among Aboriginal patients, compared with 1755 among non-Aboriginal patients. These numbers do not provide sufficient power to detect a significant difference between the groups.

The pattern of rapidly increasing incidence of ESRD among Aboriginals across Australia, especially in the NT, is not seen in NSW. Spencer et al argue that the increase in the NT is real, not due to ageing of the Aboriginal population or improved ascertainment.² The reason for this difference in incidence is not clear. It may be due to differences between the populations in apparent predisposition to renal disease or to differences in the prevalence of primary causes and promoters of chronic renal disease. The epidemic of disease in the NT is not only due to an increased prevalence of diabetes. Community screening studies show a prevalence of significant proteinuria in marked excess of the prevalence of diabetes or impaired glucose tolerance.^2,15 In the NT, from 1988 to 1993, the average annual incidence of ESRD not attributable to diabetes was 350 per million per year among Aboriginals.¹ Lower incidence of ESRD in NSW Aboriginals may reflect less profound socioeconomic disadvantage and readier access to effective primary and specialist care. However, there may be poor ascertainment, particularly in rural areas of NSW. Further study is indicated to analyse this question.

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Department of Renal Medicine, Royal Prince Alfred Hospital, Sydney, NSW.
Adrian G Gillin, FRACP, PhD, Staff Specialist;
John S Horvath, MB BS, FRACP, Professor.

Reprints will not be available from the authors.
Correspondence: Dr A Cass, Menzies School of Health Research, PO Box 41096, Casuarina, NT 0811.
alancassATmenzies.edu.au