Criteria for  Evaluating the Performance of Mycobacteriological Laboratories

 In this article you’ll be aquanted with criteria for evaluating the performance of mycobacteriological laboratories.

For the purpose of clarity of performance, mycobacterial laboratories need to give a complete annual report of their results to the center of management of contagious disorders, the health reference laboratory, and in particular, the directors of the centers that send out samples for the diagnosis of tuberculosis. This report should include a list of all patients with a positive result, the details of their lab tests as well as the degree of positiveness of their samples. Therefore, one tool for the evaluation of the performance of a mycobacteriological laboratory is to have a complete set of results of the direct smear and culture tests.

The results of the direct smear should include four degrees of positiveness (1-9, +, ++, and +++). The culture test should also include four levels of severity of the disease (the number of mycobacterial colonies that have grown on the solid Löwenstein–Jensen medium) as well as the degree of contamination of the sample.

The evaluation criteria of the direct smear test

One evaluation criterion is the knowledge about the sensitivity of the direct smear test. The reported sensitivity of the direct smear test in textbooks ranges from 20% to 80%. Higher sensitivities of the test in a laboratory is a reflection of its better performance.

The formula for the calculation of sensitivity of the direct smear test

To determine the sensitivity of the direct smear test, the results of both direct smear and culture are needed to obtain the number of true positives and false negatives.

Sensitivity =  Number of True Positives /(Number of True Positives + Number of False Negatives)

Another evaluation criterion on the performance of a mycobacteriological laboratory is its ability to diagnose the disease at the early stage when the number of acid fast bacilli is less than 9 in the smear test. Laboratories with a high quality of performance are expected to be able to identify an acceptable percentage of patients at this very early stage and to record this result in their report.

The evaluation criteria of the gold standard culture test

1. One evaluation criterion is the consistency between the direct smear and culture tests in terms of the degree of positiveness of the disease.

2. Identification of the A-typical pigmented mycobacteria (photochromogens and scotochromogens) and atypical rapid growing mycobacteria

3. The degree of contamination of culture tests. The acceptable degree of contamination throughout the culture procedure is 2%-5%.

At the end, we wish a rapid recovery for all patients

Azizollah Rezaei, Mostafa Ghalami-Nobar, Mohammad Ghahri, Soheil Modir

The scientific and administrative group of Zarifi Laboratory

164 Darya Boulevard, Paknejad intersection, ShahrakGharb, Tehran, Iran

Website: www.zarifilab.com

email: Zarifi_lab@yahoo.com                     Insyagram: @zarifilab

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