Value and significance of new diagnostic criteria of diabetes mellitus in older people

Abstract

In 1998, the World Health Organization (WHO) accepted the diagnostic criteria proposed in 1997 by the American Diabetes Association (ADA) and confirmed that, independent of age, the fasting plasma glucose (FPG) level from and above 126 mg/dl in the morning should be considered as diabetic, while subjects with FPG 110–125 mg/dl have an impaired fasting glucose (IFG), compared with the normal fasting glucose (NFG) level (up to 110 mg/dl). In a pool of 4492 elderly people (65–84 years), we assessed the significance and meaning of these new diagnostic criteria of diabetes. A 5-year follow-up was carried out, during which out of 4492 elderly subjects, 2750 were re-examined. As regards the diagnosis, we applied both the criteria of WHO (1985, 1998). At our first observation (1992), 13.1% were diabetic in the elderly group, if applying the WHO (1985) criteria, and 15.1% applying the ADA-WHO definitions. When re-analyzing the subjects with FPG of 126–139 mg/dl after 5 years, it became evident that the diagnosis of diabetes is not stable in this group, because 50.7% of them displayed FPG < 126 mg/dl (14.5% IFG; 36.2% even NFG). It means that the significance of FPG and the conditions of diabetes are different in the elderly, as compared with the younger adults. Furthermore, the oral glucose tolerance test (OGTT) of 60 elderly subjects in the age range of 71–80 years, admitted in our day hospital, were considered. Among the subjects with an FPG 126–140 mg/dl, the OGTT was of diabetic type in 90%, while among IFG and NFG subjects, it was in 50 and 10%, respectively. In conclusion, in elderly subjects with FPG of 126–140 mg/dl, the diagnosis of diabetes is not stable and requires further confirmation.

Introduction

In 1997, the ADA introduced new diagnostic criteria for gluco-metabolic alterations, establishing that, regardless the age, all subjects with an FPG ≥ 126 mg/dl should be considered as diabetics (Expert Committee on the Diagnosis and Classification of Diabetes Mellitus, 1997). Such a modification was based on a better sensibility of FPG than the 2-h post-glucose load. Furthermore, ADA introduced a new category called IFG on the basis of fasting values alone (Expert Committee on the Diagnosis and Classification of Diabetes Mellitus, 1997). These criteria emerged from the needs of an early detection of glucose dysregulation, in order to better prevent the complications related to diabetes (UKPDS, 1998, DCCT, 2001).

In 1998, the WHO agreed to ADA in the diagnostic criteria with slight modifications (WHO, 1999), recommending that all the subjects with IFG should undergo an OGTT, in order to better define their metabolic status. More recently, the ADA had even suggested a lowered threshold for NFG from 110 to 100 mg/dl (Genuth et al., 2003). Therefore, in the latter diagnostic criteria, the IFG subjects are those with an FPG ranging 100–126 mg/dl.

Some considerations have been made about the diabetic disease in older people, in relation to the casual finding of hyperglycemia in elderly without a pathological significance. It has been observed that in elderly subjects, fasting glycemia has a mean increase of 1–2 mg% for decade, and such increase is 6–9 mg% for decade after a 2-h OGTT (Andres and Tobin, 1975, Andres, 1981). Based on these last data, in 1988, the National Institute of Aging recommended that the 2-h postload glucose (2-h PLG) value should be corrected in relation to the age (Lombardo and Motta, 1990).

It is well known that the tolerance to carbohydrates progressively worsens with the increase of age (Goldberg and Coon, 1994). Furthermore, the 2-h OGTT performed to healthy people aged 65 years and over are of diabetic type in more cases than in younger adults (40–60 years) (Reaven et al., 1989, Shimokata et al., 1991, Wahl et al., 1998). The epidemiological studies have documented a progressive increase of prevalence of diabetes in the elderly (Stolk et al., 1997, DECODE, 2002). It is mainly due to an improved survival of diabetic subjects in relation to a better therapeutic treatment and to the increase in life expectancy, with a consequent onset of new cases of diabetes. In a series of 4492 elderly subjects coming from an epidemiological study carried out on a sample representative for population, we have assessed the prevalence of diabetes with the new diagnostic criteria. We also have performed a 5-year follow-up, verifying the evolution of glycemic status in the subjects re-assessed. Finally, we have performed an OGTT to 60 elderly subjects with normal fasting glycemia (NFG, glycemia <110 mg/dl), with impaired fasting glycemia (IFG, glycemia 110–125 mg/dl), and with diabetes (126–140 mg/dl), in order to verify the diagnostic sensitivity of such criteria. In order to assess the effective significance of diagnosis of diabetes in older people, we have compared the results applying ADA/WHO criteria and the previous WHO 1985 criteria.