?. SPECIMENS FOR DIAGNOSIS OF TB
A. Specimens
A variety of specimens can be collected to establish diagnosis of TB. Sputum, however, is most important specimen to be examined (1) because more then 80% of TB develop in the lung, hence they are to be diagnosed by demonstrating tubercle bacilli in sputum specimens, and (2) because transmission of infection occur by inhaling aerosolized sputum expectorated from patients so that, from the epidemiological point of view, sputum is most important specimen to examined. If it is difficult to collect sputum, then laryngeal swabs can be the next choice of specimen. Gastric washings are a choice of specimen for children because sputum collection from them is extremely difficult. However caution must be taken to the acid-fast artefacts present in gastric content on smear microscopy.
For the diagnosis of extra-pulmonary tuberculosis care should be taken to collect specimen deriving from the lesions.
B. Sputum containers
Selection of sputum container is not easy. A wide mouthed, reusable glass containers with water tight lid are used in some countries, while disposable plastic containers are widely used in many other countries. If the specimens are sent to the other laboratory, sputum containers must be put into a box in safe not leak or break down during transport and to protect from heat and direct sunlight.
C. Sputum collection
1. Subjects for sputum examination
From whom sputum specimens should be collected for case-finding? In order to maximize prevention of new TB infection in the community, smear-positive cases must be found as early as possible. It seems to be attainable because over 90% of those cases develop perceptible symptoms within a few weeks of the onset of TB. Under the programme condition, the peripheral health workers should approach to high risk groups such as symptomatics among family contacts of known cases or other risk groups.
It has been observed elsewhere that sputum positive-cases were found over six times more often among symptomatics than asymptomatics. The most common symptom of pulmonary tuberculosis is a persistent cough for three weeks or more, usually accompanying by one or more of following symptoms: weight loss, fatigue, fever, night sweats, chest pain, shortness of breath, loss of appetite, and haemoptysis. The more concurrent symptoms existed, the more cases found. In general, most of sputum positive cases have overt symptoms relevant to tuberculosis, many of them do not know that the symptoms have been resulted from TB and some patients do not realize seriousness of such symptoms.
2. How to collect sputum collections
What type of sputum specimens should be collected from the suspects to establish the diagnosis? As seen in table 1, overnight morning sputum collected at patient's home were superior over spot sputum in case-yield rate especially on smear examination. In all studies, overnight sputum produced 1.6-2.3 times more cases on smear microscopy than spot sputum, but less remarkable difference on culture examination. Home collected specimens usually show relatively high contamination rate. However, if sputum collection entirely rely on overnight specimen, many patients may be evaded from sputum examination. For this reason, it is strongly recommended to collect the first specimen always on the spot.
