How to Optimize Current (Available) Diagnostic Tests

Abstract

Isolation of mycobacterium tuberculosis is the gold standard in the diagnosis of childhood tuberculosis. However, it has inherent limitations due to paucibacillary nature of the disease in children and technical difficulties encountered in collection of appropriate sample. Thus, diagnosis is dependent on circumstantial evidence at best supported by conventional tests such as tuberculin test and chest radiograph. Several new tests are being developed but they lack ideal sensitivity and specificity. Hence, it is important to optimise use of current diagnostic tests. Clinical suspicion based on protocol developed by IAP is a pre-requisite of ordering tests and it is only then that proper interpretation is possible. Tuberculin skin test is still a useful screening test. It does help in establishing presence of infection though not necessarily disease. Attention must be paid to ideal test solution, proper technique and cautious interpretation. BCG test is not recommended. Miliary shadows and fibrocaseious cavitary lesions in chest radiograph are highly suggestive of tuberculosis in our epidemiology. CT scan is rarely necessary and is not cost and radiation-effective. It is ideal to attempt bacteriological examination in every suspected case of childhood tuberculosis. Most practical method is collection of gastric aspirate for smear and culture. It is possible to carry out this procedure in out-patient clinic. Better yield is likely with increasing expertise especially in extensive disease. Bronchoalveolar lavage is an invasive test and bacterial yield is comparable to that of gastric aspirate. Tissue collected for histopathological examination must be submitted for bacteriological tests. PCR is not easily available. It has high sensitivity but lower specificity and thus, is not routinely recommended. Serology has no place in diagnosis of tuberculosis. Interferon gamma release assays are also now available. Sensitivity and specificity of Quantiferon Gold and T-spot tests have not been studied in children and hence are not recommended in routine practice. Instead of trying newer tests, it may be best to avail an expert advice in difficult cases.

The Six-Year Retrospective Results of Tuberculosis Laboratory and Anti-mycobacterial Drug-Resistance Rates

“…Genel olarak bakıldığı zaman TB tanısı için laboratuvara sıklıkla gönderilen örnekler balgam başta olmak üzere, bronkoalveolar lavaj ve gastrik aspirattır [15][16][17]. Çalışmamızda balgam ve BAL, örneklerin yarısından fazlasını (%53.4) oluş-turmaktadır.…”

“…Kültür yöntemi için uygun örnek alınması, örneğin uygun bir şekilde nakli, uygun ekimi ve değerlendirilmesi mikroorganizmanın tespit edilme şansını arttıracaktır [16]. Balgam örneğinde mililitrede basil sayısının 5000-10000 arasında olması, özellikle hastalığın başlangıç aşamasında bakterinin mikroskobi ile tespit edilme şansını azaltmaktadır.…”

Interferon-γ Release Assay for the Diagnosis of Latent Mycobacterium tuberculosis Infection in Children Younger Than 5 Years

“…The following are the advantages of the new IGRAs: no return visit is necessary as in the case of TST; there is no boosting effect; and it is unaffected by previous BCG vaccine and exposure to atypical mycobacteria. 6 Commercially available IGRAs for mats include QuantiFERON-TB Gold (QFT-G), QuantiFERON-TB Gold in-Tube (QFT-G-IT) (Cellestis Ltd, Carnegie, Victoria, Australia), and the T-SPOT.TB test (Oxford Immunotec, Oxford, UK). The role of IGRAs for children with LTBI or suspected TB disease has been poorly defined.…”

Childhood Tuberculosis Challenges and Way Forward

“…In the absence of a gold standard, there is both under and over diagnosis of tuberculosis. In this issue, two related articles discuss the available clinical algorithms for diagnosis [6] and optimal utilization of diagnostic tests in day to day clinical practice [7].…”