Untreated tuberculosis may be associated with lymphopoenia, not lymphocytosis.

Initial full blood counts were compared in 25 consecutive adult patients admitted with active tuberculosis and 25 matched, healthy controls and, if available, repeated at 6 and 12 months during treatment. Patients with tuberculosis had significant lymphopoenia associated with anaemia, neutrophil leucocytosis and monocytosis. None of these derangements correlated with radiological extent of lung disease or cutaneous tuberculin reactivity. Lymphocyte counts returned to normal within 2 weeks of initiating chemotherapy in all lymphopoenic patients and normal ranges for all blood counts were restored by 6 months in all the patients studied. In a smear-negative patient, a clinical diagnosis of tuberculosis would be supported by the finding of lymphopoenia, not lymphocytosis.