The clinical biochemistry of anorexia nervosa

In anorexia nervosa, under-nutrition and weight regulatory behaviours such as vomiting and laxative abuse can lead to a range of biochemical problems. Hypokalaemia is the most common electrolyte abnormality. Metabolic alkalosis occurs in patients who vomit or abuse diuretics and acidosis in those misusing laxatives. Hyponatraemia is often due to excessive water ingestion, but may also occur in chronic energy deprivation or diuretic misuse. Urea and creatinine are generally low and normal concentrations may mask dehydration or renal dysfunction. Abnormalities of liver enzymes are predominantly characterized by elevation of aminotransferases, which may occur before or during refeeding. The serum albumin is usually normal, even in severely malnourished patients. Amenorrhoea is due to hypogonadotrophic hypogonadism. Reduced concentrations of free T4 and free T3 are frequently reported and T4 is preferentially converted to reverse T3. Cortisol is elevated but the response to adrenocorticotrophic hormone is normal. Hypoglycaemia is common. Hypercholesterolaemia is a common finding but its significance for cardiovascular risk is uncertain. A number of micronutrient deficiencies can occur.