Part II: Microscopy
recording and reporting of results

The microscopic observation must establish, first of all, if there are acidfast bacilli present in the smear and, if so, the approximate average number of these bacilli per microscopic field observed. It is recommended that a uniform pattern of reading is followed, observing 100 useful fields. A useful microscopic field is regarded as one in which cellular elements of bronchial origin (leucocytes, mucuous fibres and ciliated cells) are observed. The fields in which there are no such elements should not be included in the reading.

Negative
Indicate the staining method. Report ?negative for acid-fast bacilli? for all smears in which no acid-fast bacilli have been seen in 100 fields.

Positive
Indicate the staining method. The number of acid-fast bacilli found is an indication of the degree of infectivity of the patient as well as the severity of tuberculosis disease. Results should therefore be quantified. For Ziehl-Neelsen stained smears the following semi-quantitative method of reporting is recommended:

Quantification of Ziehl-Neelsen smear results
Quantification of fluorochrome smear results
When fluorochrome staining methods are used, smears are examined at much lower magnifications (typically 250x to 630x) than those commonly used for carbolfuchsin-stained smears (1 000x). Each field examined under fluorescence microscopy, therefore, has a larger area than that seen with bright field microscopy. Thus, a report based on a fluorochrome-stained smear examined at 250x may contain much larger numbers of bacilli than a similar report from the same specimen stained with carbolfuchsin and examined at 1 000x. To minimise confusion that conceivably could occur when different magnifications are used for smear examination and quantitative reporting of results, a method has been suggested whereby the number of acid-fast bacilli observed under fluorochrome staining could be divided by a ?magnification factor? to yield an approximate number that might be observed if the same smear were examined under 1 000x after carbolfuchsin stain.

A simple table using the magnification factors enable reports to be comparable from laboratory to laboratory regardless of the stain or magnification used: 

Example: Suppose 20 acid-fast bacilli are observed per field using the 450x magnification. If this number is divided by the magnification factor of 4 according to the table, the comparable number of bacilli that would have been observed under 1 000x is 5 per field. The laboratory result should therefore read 2+, and not 3+, as originally indicated by 20 acid-fast bacilli per field.

The microscopy report should be made available as soon as possible, preferably with no more than 24 hours delay from the moment of receipt of the specimen in the laboratory. The final microscopy report should contain the following information:

• evaluation of the quality of the sputum specimen
• the staining method used
• the average number of acid-fast bacilli seen on the smear
• indication of any large numbers of clumps, which means that the actual number of acid-fast bacilli may be larger than reported
• report only the number of acid-fast bacilli seen: do not try to identify the mycobacterial species
• the date of examination and the microscopist?s signature
• always send a report to the referring health centre. Never give the results only to the  patient. If s/he fails to bring the results to the health centre, s/he may not receive the necessary treatment

A model microscopy report form is presented in Annex 4.

All smear results should be recorded in the laboratory register, which should contain the following information: patient name, sex, age, name of health centre and patient number, reason for examination (diagnosis or follow-up of chemotherapy), microscopy results and remarks (if necessary). It is recommended that positive results be written in red ink. Individual patient reports should then be prepared from the laboratory register.

A model laboratory register is presented in Annex 5.