Sputum smear examination by ZN staining, culture examination by egg media, and DNA examination cost 3 US dollars, 21 US dollars, and 60 to 75 US dollars respectively.
6) Comparison of smear, culture, DNA exam.
Differences of smear, culture, and DNA examination are summarized here by the cost, personnel required, rapidity to obtain the result and sensitivity to get positive result.
Every technique has advantages and disadvantages depending on circumstances. For this reason, the procedures to be employed into NTP must be carefully selected taking into account of sensitivity, specificity, simplicity, economy, and maximal security.
Once selected they must be well standardized and always carried out under strict quality control and supervision.
Although there are a variety of laboratory procedures to demonstrate TB bacilli in sputum, the basic and priority technique in current use to NTP is sputum smear examination due to the object of NTP.
[□] SPUTUM SMEAR MICROSCOPY
7) Picture of ZN and Fl
In all aspects, smear microscopy is a priority procedure over any other techniques in case-finding and in monitoring patients response to chemotherapy in NTP.
ZN staining method and fluorescence staining method are widely used in the world. By ZN staining method, AFB in sputum can be stained red and the background material is stained blue. And by fluorescence staining method, AFB fluoresce green against the dark background as it is shown here.
8) Comparison of ZN and Fl
ZN microscopy is cheaper than fluorescence microscopy in terms of price and running cost or maintenance of microscope. The price of fluorescence microscope is 7 to 10 times higher than light microscope and bulb for light source of fluorescence microscope cost 400 US dollars used only for 200 hours.
ZN microscopy is cheap and provides fast results. The technique is of adequate sensitivity and specificity and economical, particularly in a small microscopy center examining less than 30 specimens a day.
Fluorescence microscopy is suitable to σ busy laboratory such as intermediate or central laboratory where large number of specimen is processed daily. Fluorescence microscopy allows to scan at least 17 times wider microscopic field than the light microscopic field due to the application of low power of lens.
However, Fluorescence microscopy does not permit to pick up more positive but reduce the scanning time.
There is no significant difference in case yields between ZN and fluorescence methods.
But if a smear contains few bacilli, false positive are more often encountered with fluorescence method than ZN method. So that scanty positive slide by fluorescence microscopy should be confirmed by ZN staining.
9) ZN staining method
Sputum smear examination by ZN staining method consists of four parts as shown here; smearing, staining, microscopic observation, recording and reporting. Detailed procedures are described in the manual.
10) Sputum collection
During smear microscopy process, collection of good quality of specimen is the key to obtain reliable results.
Three times of sputum collection is recommended within 2 days, namely; 1)spot sputum obtained when people come to a TB microscopy center, 2)following morning sputum, and 3)spot sputum obtained when they come to the TB microscopy center for the second time to deliver the morning sputum specimen. These increase the high probability of finding AFB.
11) Studies of Sputum Collection
4 studies on sputum collection are introduced here.
Most of the studies showed that 80 to 86% of smear positive cases could have been diagnosed with the first sputum specimen. The second specimens yielded 10 to 14% additional positives. More than 2 specimens did not increase number of additional positives significantly.
Therefore, minimum 2 or maximum 3 specimens are required to collect from one symptomatic, if the first or second specimen showed a negative result on smear microscopy.
12) Sputum quality
Sputum quality affects also to the case yield rate to a great extent as shown here.
Mucopurulent sputum specimens produced approximately 20 times more positives on smear examination than the salivary specimens.
