Question category: Endocrinology
A patient presents with weight loss, polyuria and polydipsia. He is found to have a normochromic, normocytic anaemia and high fasting glucose. He is also complaining of diarrhoea. On examination there is evidence of stomatitis and erythematous rash in his groins and and on his legs. There is areas of hyperpigmentation. He states the lesion began a couple of weeks ago beginning as flat rings then blistered and were itchy and painful. Which investigation will be most useful for the diagnosis?