Management of obesity

To the Editor: I read with interest the recent article on obesity in Australia by Proietto and Baur1 and would like to comment on the issue of proteinuria and measurement of insulin level in obese patients.

Proteinuria in obesity, commonly referred to as obesity-related glomerulopathy, is a clinical syndrome with an estimated incidence of about 2% in obese subjects.2 With a fifth of the population being obese,1 the sheer number suspected to have this condition will create an enormous management and cost burden. Furthermore, the incidence of this condition appears to have increased disproportionately to the incidence of obesity.2

The syndrome of obesity-related glomerulopathy comprises the triad of morbid obesity, marked proteinuria without oedema, and normal serum albumin concentration. It can occur in any degree of obesity but is more common in the morbidly obese group (body mass index > 40 kg/m2; Class III obesity). It often presents as proteinuria on urinary dipstick testing, with marked proteinuria seen on confirmatory testing (up to 32 g/day).2 Other features of the nephrotic syndrome do not occur, and the cholesterol level is often lower than that in patients with nephrotic syndrome. However, glomerular filtration rate is raised, and glomerulosclerosis is seen on biopsy. The pathogenesis is unknown.

Obesity-related glomerulopathy is a diagnosis of exclusion: secondary causes of proteinuria should be fully eliminated, including hypertensive renal disease and undetected type 2 diabetic renal disease. More often than not, biopsy will be required to guide management, with cost implications.

Although the condition is said to be benign, in a small proportion of patients it progresses to end-stage renal failure requiring replacement therapy, further adding to the cost of management. Fortunately, the condition is readily reversible with weight loss, which is an important emphasis in management. 3

My second comment relates to the case of the overweight adolescent described by Proietto and Baur. In this patient, measurement of insulin level is not indicated.4 There is no standardised insulin immunoassay, the sample has to be collected and processed correctly to produce a valid result, and the result would not add to or alter the management of the condition. It is doubtful if normative data exist for adolescents, but the clinical picture suggests the insulin resistance syndrome. As the primary goal would be to detect disordered glucose metabolism, appropriate testing of glucose level is all that is required.