A woman is admitted with complains of low-grade fever of 6 weeks duration. Chest radiograph reveals bihilar adenopathy with clear lung fields. All of the following investigations will be useful in differential diagnosis except :

Answer is A (CD4/CD8 counts in the blood) : The patient in question is suffering from sarcoidosis. `While there is marked enhancement of no. of TH cells at the sites of disease the number of TH cells in the blood are normal' - Harrison `Where as TH cells in the involved organs are proliferating at an enhanced rate the T cells in other sites such as blood are quiescent' - Harrison It is the CD4 / CD8 counts in the affected organs which is an impoant ancillary aid in established the diagnosis of sarcoidosis and not the CD4 / CD8 count in the blood as specifically asked in the question. Active sarcoidosis results from an exaggerated cellular immune response resulting in accumulation of large no. of T4 cells in the affected organs, where the ratio of CD4 to CD8 cells may be as high as 10:1. Although CT of chest is also only rarely helpful, it may identify early fibrosis and active alveolitis and thus contribute to a diagnosis of sarcoidosis.