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NHANES III : Correlation between microalbuminuria and the metabolic syndrome

The metabolic syndrome is associated with a cluster of disorders such as abdominal obesity, insulin-resistance, hypertension, and dyslipidaemia. This study is the first to assess the correlation between microalbuminuria as defined by WHO and the metabolic syndrome defined by NCEP ATP III criteria) in a large US population.

Palaniappan L, Carnethon M, Fortmann SP. Association between microalbuminuria and the metabolic syndrome: NHANES III. Am J Hypertens 2003;16:952-8.

Microalbuminuria, a strong predictor of cardiovascular (CV) mortality, is related to hypertension (HT) and central obesity, which are both components of the metabolic syndrome (MetS). Microalbuminuria is thought to be the renal expression of endothelial damage, and an early indicator of atherosclerosis. However, previous studies evaluating the relationship between microalbuminuria and MetS were limited in number of subjects.

Participants
The Third National Health and Nutrition Examination Survey (NHANES III) was conducted between 1988 and 1994 in the US; survey participants were non-Hispanic white, African-American, and Mexican-American. The present investigation included 5659 men and women aged over 20 and under 80 years old.

MetS was defined according to the new National Cholesterol Education Program-Adult Treatment Panel (NCEP-ATP) III definition, as three or more of the following criteria:
abdominal obesity: waist circumference (>102 cm in men and >88 cm in women)
hypertriglyceridaemia: ≥150 mg/dl (1.69 mmol/l)
low HDL-cholesterol: <40 mg/dl (1.04 mmol/l) in men and <50 mg/dl (1.29 mmol/l) in women
high blood pressure (BP): systolic BP ≥130 mm Hg and diastolic BP ≥85 mm Hg
high fasting glucose: ≥110 mg/dl (≥6.1 mmol/l)

Microalbuminuria was defined as a urinary albumin-to-creatinine ratio (ACR) of 30 to 300 mg/g.

Microalbuminuria as a component of MetS
Microalbuminuria was found in 7.8% of women and 5.0% of men. Log-linear analysis showed a significant correlation between MetS and microalbuminuria in both men and women (χ2 = 44.1 for women and 59.6 for men, both P<0.0001). The prevalence of microalbuminuria was higher in women and men with MetS (odds ratio [OR] = 2.2 for women; 95% confidence interval [CI]: 1.44 to 3.34, and 4.1 for men; 95% CI: 2.45 to 6.74). The overall prevalence of MetS was 19.8% in women and 17.2% in men, while 33.9% of women and 41.5% of men had both MetS and microalbuminuria. The Figure shows the prevalence of MetS according to the presence or absence of microalbuminuria.

The strength of the association between microalbuminuria and MetS remains significant after adjustment for age and other MetS components. This suggests that microalbuminuria may be a component and/or a consequence of MetS. Moreover, microalbuminuria, which has long been associated with HT, reflects early renal dysfunction, and may provide another perspective for the treatment of MetS.

Correlation between high glucose level and Microalbuminuria
After adjusting for other components of MetS, HT and hyperglycaemia demonstrated a strong association with microalbuminuria in men and women (Table). Even while excluding HT as a MetS component, the correlation between microalbuminuria and MetS remained significant (after adjustment for age: OR in men = 2.3; 95% CI: 2.1 to 5.7, and OR in women = 1.6; 95% CI: 1.1 to 3.1).

*OR = Odds ratios, adjusted for all other components in the table. TG : triglycerides.

This was the first time a study focused on the correlation between a high glucose level according to the NCEP-ATP III definition and microalbuminuria. These results indicate that a fasting plasma glucose level of >110 mg/dl is strongly related to microalbuminuria. The prevalence of microalbuminuria is greatest in the presence of both diabetes and HT, but this study extends the findings to lower levels of BP and glucose.

Microalbuminuria as a risk prediction tool
Microalbuminuria is known to be a CV disease marker and a strong predictor of CV morbidity and mortality. Diagnosis of microalbuminuria along with other components of MetS may increase the specificity of the risk prediction, and explain the increased CV risk observed in MetS.

The NHANES III study, one of the largest surveys performed in the US, is a representative sample of the US population. Results can therefore be extrapolated in order to evaluate prevalence in the US population at large.

In summary, microalbuminuria is strongly associated with MetS and particularly with two of its components, high glucose level and high BP. MetS may be associated with serious renal dysfunction, and physicians should consider measuring urinary albumin.