Routine blood and urine examinations in pulmonary tuberculosis are as non-specific as those of physical examination. The patient may be found to be anaemic with a normal or raised WBC count.
Erythrocyte sedimentation rate (ESR)
ESR is o a non-specific investigation which may become rapid in a large variety of clinical conditions ranging from anaemia to any chronic infectious, inflammatory or malignant disease.
ESR has absolutely no diagnostic value for TB and should not be given any weightage at all towards its diagnosis as a standalone criteria. But in conjunction with other clinical parameters, its raised value can indicate possibility of tuberculosis
Sputum examination
Examination of the sputum is the only way by which a definitive diagnosis of pulmonary tuberculosis can be made. You can be absolutely certain that your patient has pulmonary TB only when his sputum smear is positive for AFB. The importance of this investigation cannot be overstated. Vigorous efforts should be made to isolate AFB in sputum before initiating treatment.
Useful tips
- The patient should preferably give samples on three days. In case of inconvenience, a ‘spot’ sample to the laboratory on the first day, return the next day with an early morning sample and give a third, ‘spot’ sample, the same day. The chances of finding AFB in sputum are much higher with 3 samples than with 2 or 1 sample
- Give clear instructions to the patient to give sputum and not saliva for examination. Instruct the patient to produce the specimen by a vigorous cough and give the thick, white, yellow or green sputum thus expectorated from the lower respiratory tract.
- It is preferable to transfer the sample to the laboratory on the same day in a clean, wide mouth glass container.
- Send samples to a reliable laboratory that routinely handles a large number of sputum specimens every day.
- Wherever there is a high index of suspicion, but the first two samples are negative for AFB by smear, and a reliable laboratory is available, send the third sample for both smear and culture examination.
Common reasons for a negative report
- Poor or no instructions by doctors to patients
- Poor staining the smear also contributes towards underdetection of AFB in sputum.
- Too few or no bacilli in the sputum
The patient whose sputum smear is persistently negative may have some other disease. However, if you still strongly suspect pulmonary TB clinically and radiologically, repeating sputum smear examination after 3-4 weeks may be worthwhile.
