Primary care providers in New Zealand (NZ) are paid to provide an annual diabetes review to all patients diagnosed with diabetes types 1 and 2. District health boards in NZ have targets for increasing the proportion of patients with diabetes who receive the free annual diabetes check.1 This is to be achieved across all ethnic groups. Currently there are minimal data indicating the expected number of patients in general practices and it is difficult to assess the coverage of this programme.2 Ministry of Health estimates indicate that approximately 64% of patients received checks in 2007, but uptake among Māori people in particular (39%) is suboptimal.1 Until there are complete population-based diabetes registers more widely available, the success of district health boards in evaluating their performance against targets will depend on more accurate data on the expected prevalence of diabetes.

The ethnic make-up of NZ is predominantly European (68%), while indigenous Māori account for 15% for the population.3 Pacific people (7%) and Asians (9%) have also been increasing in numbers in recent years owing to immigration. It has been well recognised that Māori people have a higher prevalence of diabetes.4 Rising rates of obesity and sedentary lifestyle have resulted in diabetes reaching epidemic proportions among Māori. Māori are particularly vulnerable, with disparities for diabetes complications (renal failure, lower limb amputations, eye problems and heart disease) being disproportionately higher.5 The burden of diabetes and its complications among Pacific people and Asians is similar to that among indigenous Māori. General practice-based age-specific prevalence rates by ethnicity are not available in NZ.

There is interest in reducing inequalities for people who are economically disadvantaged.6 As in the UK,7^–9 the prevalence of diabetes has been shown to be inversely related to socioeconomic status in NZ.10 11 But it is not known whether the trend is similar across ethnic groups. Māori and Pacific people are over-represented in the most deprived categories. Diabetes risk factors such as obesity, reduced physical activity and smoking are also more prevalent among the most deprived groups.12 13 There is a significant association between deprivation index and hospital discharge rates for diabetes among NZ Europeans, but no such relationship has been found for Māori.14 The impact of socioeconomic deprivation on the prevalence of diabetes among Māori is not clear.

The use of computers by NZ general practices is one of the highest in the world.15 General practices in NZ use the UK Read Code disease coding system to capture diagnostic information,16 although diagnosis codes are not consistently recorded in compliance with national minimum dataset standards.17 Almost all NZ general practitioners (GPs) use a Practice Management System (PMS) software application and nearly two-thirds of practices use the Read Code system for coding for clinical diagnoses.15 The PMSs used in general practices also store self-defined ethnicity for all patients and capture complete prescribing data. Ethnicity is routinely recorded in NZ general practices. Although the practice system can hold up to three ethnicity responses, for reporting purposes if more than one response is given a prioritised ethnicity is used, whereby each case is allocated to a single ethnicity.18 The order of prioritisation is Māori, Pacific, Asian, other groups, and then NZ European. There are issues around the completeness of ethnicity recording,19 with variations between practices.17

The Rotorua General Practice Group (RGPG) has for many years concentrated on improving the quality of care for its patients with diabetes. There are a high proportion of Māori people living in Rotorua district: 36.4% Māori compared with 14.6% Māori in the total population of NZ.20 This study looks at the prevalence of diagnosed diabetes among Māori and NZ Europeans and the influence of deprivation on the prevalence of diabetes.

METHODS

The RGPG provides services to 65 940 people living in and around Rotorua, NZ. These patients are registered with 15 practices. A cross-sectional survey was conducted on all patients registered with any one of the 10 RGPG practices that took part in this study. The survey identified all patients registered with the practices on 1 July 2007. Patients with diabetes were initially identified by searching the practice systems for all those with a diagnostic code for diabetes or diabetes annual review. Further case identification was sought by identifying all patients with a prescription of insulin, metformin or diamicron who did not have a diagnosis of diabetes and then checking with the notes and the GP to confirm whether the patient should be on the register. The laboratory records of all RGPG patients were then checked to identify any patient with a glycosylated haemoglobin level (HbA_1c) greater than 6.5% and similar additional validation was performed using the patient records and review by the GP. Only validated cases were included in the study. Identification of undiagnosed diabetes was not attempted in this study. A previous survey by the RGPG had been carried out in 2006 linking the local retinal screening register with the diabetes register; this further check was therefore not repeated. Thus a very sensitive search was used to identify patients by looking for diagnostic codes, prescriptions, laboratory tests and records of retinal screening. Specificity was ensured by review of each patient’s chart in conjunction with the relevant GP in cases where there was no diagnosis code in the record but other evidence suggesting diabetes. A comprehensive diabetes register was formed.

Ethnicity data recorded at level 2 of the Statistics New Zealand Ethnicity Classification, which is the standard for health sector data collections in NZ, were aggregated for analysis into ethnic groups. NZDep2001 quintiles were used as the key indicators of socioeconomic status. NZDep2001 is an area-based index of socioeconomic deprivation that measures the level of deprivation for each meshblock, according to a combination of Census 2001 variables (ie, income, transport (access to car), living space, home ownership, employment status, qualifications, support (sole-parent families) and access to a telephone).21 Meshblocks are geographical units defined by Statistics New Zealand, containing a median of approximately 90 people in 2001. In NZDep2001 quintile categories, quintile 1 represents the least deprived and quintile 5 the most deprived. RGPG has assigned NZDep2001 scores to patients based on their address.

Statistical analyses

All patients registered with the practices as of 1 July 2007 were included in the denominator for prevalence calculation. The prevalence of diagnosed diabetes among general practice-registered patients by ethnicity, age group, gender and NZDep2001 quintiles was calculated. Pacific Islanders and Asians were excluded from further analysis by deprivation and gender owing to small patient numbers. It was not possible to track patient migration and changing providers within this cross-sectional study. Adjusted odds ratios for the risk of diabetes were obtained from logistic regression analysis. All statistical analyses were performed using SAS V.9.1.

RESULTS

The registered patients were 61% European, 33% Māori, 3% Asian and 1.6% Pacific Islander. Of these, 49% were male and 41% were above 40 years of age. The distribution in NZDep2001 quintiles 1–5 were 18% (least deprived), 13%, 13%, 22% and 32% (most deprived), respectively, with over-representation of Māori in the most deprived quintiles (fig 1).

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Figure 1

Ethnic composition of the patients included in the study by NZDep2001 quintiles.

Of the 45 500 patients registered with the RGPG, 2027 were identified through record searches to have some evidence of diabetes. Two hundred and eight patients, identified from laboratory results or prescriptions, could not be validated as having diabetes and were excluded from the study. Following validation, 1819 patients with previously diagnosed diabetes were included in the study.

All patients had their ethnicity recorded. Patients with diabetes included 1055 (58%) Europeans, 635 (35%) Māori, 41 (2.3%) Pacific Islanders, 60 (3.3%) Asians and 15 (0.8%) other ethnicities; 1001 (55%) were male; 248 (14%) were in quintile 1; and 688 (38%) were in quintile 5. Prevalence rates were consistently higher for males than for females among Māori and NZ Europeans (fig 2). The age-standardised prevalence of diabetes was significantly higher among males than among females (prevalence and 95% confidence intervals (CIs): Māori females 6.32% (6.31 to 6.32), Māori males 7.87% (7.86 to 7.88), NZ European females 2.532% (2.530 to 2.535) and NZ European males 3.609% (3.606 to 3.612)).

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Figure 2

Prevalence (%) of diabetes by 10-year age bands and gender among (a) Māori and (b) Europeans.

The prevalence of diabetes by age group varied widely across the ethnic groups (table 1). In the 40+ age groups, Māori and Pacific people had around three times the prevalence compared with NZ Europeans. Asians had around twice the prevalence compared with Europeans in these age groups.

With increasing deprivation, the age-standardised prevalence of diabetes increased among European males (2.7% to 5.0%) and females (2.1% to 3.1%). However, the prevalence of diabetes was highest among the least deprived Māori males (9.7%). Among Māori females, the prevalence of diabetes among the least deprived was higher (6.2%) than that for quintiles 2–4 (table 2).

After adjustment for age and gender, the most deprived (quintile 5) Europeans had nearly twice the risk of having diabetes compared with Europeans in quintiles 1–3 (table 3). The adjusted risk of diabetes for the most deprived Māori was not significantly different from that for the least deprived Māori. However, the most deprived Māori had a significantly higher risk of diabetes than Māori in quintiles 2 and 3.

DISCUSSION

This study has looked at the prevalence of diagnosed diabetes by ethnicity and socioeconomic deprivation in a general practice population. The observed prevalences of diagnosed diabetes among Europeans and Māori in NZ are in agreement with official estimates derived from other sources.22 Our finding that the prevalence of diabetes rises with increasing deprivation among Europeans is similar to results from national10 11 and international studies.7 23 24 The trend among Māori seems to be different because the least deprived are equally at risk of diabetes. National survey results regarding the influence of social deprivation on the prevalence of diabetes have not been adjusted for the over-representation of Māori in quintiles 4 and 5. Using ethnicity-specific analyses, we have confirmed the association between social deprivation and prevalence of diabetes among Europeans. We also showed that a similar trend does not hold true for Māori.

Although Rotorua has a high proportion of Māori, we believe that those living in Rotorua are similar to Māori living elsewhere in NZ, with respect to their levels of obesity, lifestyle and other risk factors for diabetes. It is reasonable to generalise the present findings to the nation’s Māori population.

Age, obesity, sedentary lifestyle and smoking are the main risk factors in the progression from the ‘pre-diabetes’ state to type 2 diabetes.25^–27 Generally, the association between socioeconomic status and diabetes has been attributed to the differences in risk factors, with the rates of obesity, poor diet, sedentary lifestyle and smoking being higher among people living in more deprived areas.13 23

Analysis of the 2002/03 Health Survey data, in which deprivation quintiles 1 and 2 were merged to form the least deprived category, revealed that Māori males exhibit an inverse relationship between body mass index (BMI) and deprivation.28 That is, the least deprived Māori males tend to be heavier and of wider girth (median BMI 29.3 kg/m²) than their less advantaged counterparts (median BMI 28.5 kg/m²). Māori females by contrast show a direct relationship: increasing BMI/waist circumference with increasing deprivation. But even the least deprived Māori females had a median BMI of 25.6 kg/m². This trend is quite different from the non-Māori population in NZ, where the median BMI values of the least deprived categories are much lower (25.7 for males and 23.9 for females) than the most deprived (26.3 for males and females). In this study, the impact of BMI on diabetes risk could not be assessed since it was not available for patients without diabetes, but obesity might be important contributor to the differences seen between Māori and Europeans in NZ.

In developing countries such as India,29 30 Bangladesh,31 China,32 Malaysia33 and Africa,34 the prevalence of diabetes is lower among those with a low income than among more affluent groups. This trend is consistent with lower BMI values among low-income groups in these countries. But developed countries experience higher prevalence rates of obesity and diabetes in more deprived areas. After adjustment for body size, the relationship between socioeconomic status and diabetes among indigenous Australians35 and African Americans36 is consistent with the patterns observed in Europeans.

Another postulated explanation for the finding that the least deprived Māori have a higher prevalence is that it is a detection issue, that is, the least deprived are more likely to visit the doctor and therefore are more likely to be diagnosed. In the UK, undiagnosed diabetes is more prevalent among the poorest than among the richest women.37 Māori, in general, are less likely than Europeans to visit a doctor and are more likely to report an unmet need for a GP.11 But it is not clear whether diabetes detection rates vary with social deprivation among Māori. There is evidence that the rates of doctor consultations increases with socioeconomic deprivation among Māori and Europeans in NZ general practices.38 So it is possible that diabetes detection is not compromised in the most deprived groups.

Higher proportions of Māori live in the most deprived geographical areas. In 2001, 39% of Māori lived in the most deprived quintile 5 areas (compared with 15% of non-Māori), while only 6% of Māori lived in the least deprived quintile 1 areas (compared with 16% of non-Māori).39 The modifiable risk factors (obesity, smoking and reduced physical activity) are more prevalent in populations of low socioeconomic status.13 23

There is strong evidence that the progression of type 2 diabetes can be delayed or prevented with lifestyle programmes that promote a healthy diet and physical exercise.40^–42 NZ Europeans benefit from diabetes prevention programmes targeting socioeconomically deprived groups. But, for Māori, interventions should be tailor-made to include the least deprived groups as well. More research is needed into the role of obesity in the observed differences in the prevalence of diabetes across deprivation quintiles among Māori.