If available, digital imaging can be used in the diagnostic work-up of PTB similar to a chest film if the appropriate standards are followed.
Summary of evidence
The utilization of digital imaging, improvements in data storage and availability of high speed internet have all paved the way for tele- radiography practice in the Philippines. Tele-radiography is defined as the transmission of imaging studies electronically or through a digital storage media from one location to another for the purposes of interpretation and/ or consultation. Its main goal is to link the expertise of on- and off-site radiologists to ensure access to imaging interpretative services by health care facilities in the country and abroad to help achieve delivery of optimum patient care. Images can be adjusted electronically to optimize evaluation of the chest x-ray, achieve rapid processing with fewer repeat examinations, and lesser radiation exposure. Likewise, images can be efficiently stored, archived and can easily be retrieved for comparison and monitoring of patients undergoing or who have already finished treatment.
For digitized radiographic films, the recommended minimum specifications are 2.5 lp/mm spatial resolution with an 8-bit pixel depth. The display stations must be able to accurately reproduce the original study with capabilities in window and level adjustments, zoom (magnification) and pan functions, rotating or flipping images, and perform linear measurements. Digital studies, however, will not improve poorly acquired images.
It is emphasized that facilities must be duly licensed by the Department of Health (DOH) and comply with specific technical standards of Digital Imaging and Communications in Medicine (DICOM) and the Philippine College of Radiology (PCR) for the acquisition of new and upgrading of equipment, image capture and data management including storage of records. QUESTION 17 What is the role of chest CT scan in the diagnosis of PTB?
The routine use of chest CT scan in the diagnosis of active pulmonary tuberculosis cannot be recommended, unless other co-existing disease conditions are highly considered to explain the patient’s presentation, or to evaluate possible complications or sequelae of PTB. Clinical correlation and bacteriologic confirmation should still be done. (Strong recommendation, moderate quality evidence) Summary of evidence
In general, chest CT scan has a 91% sensitivity and 76% specificity rate in diagnosing pulmonary tuberculosis compared to the sensitivity rate of 49% for a plain chest radiograph. There are certain advantages of this modality with its ability to detect subtle changes which may be due to
TB. High Resolution CT (HRCT), in particular, is able to detect small cavitations within areas of consolidation or dense scarring in a number of cases. Other findings which have been documented to be associated with bacteriologically confirmed cases include peculiar patterns of parenchymal abnormalities, presence of cavitations or evidence of endobronchial spread (i.e. presence of centriblobular nodules or tree- in-bud pattern). CT scan may be also useful in evaluating the pleural structure for possible complications or TB sequelae such as presence of effusion, empyema or broncho-pleural fistula.
The routine use of this modality to diagnose active TB cannot be recommended at the moment. Its potential added cost and increased radiation exposure may further limit its utility as an initial screening tool. However, chest CT can possibly complement other diagnostic tests because of its ability to present parenchymal structures in greater detail. This aspect was supported in a study by Lee and colleagues where cases of PTB were established when HRCT was utilized as a complementary imaging modality. QUESTION 18 What are the recommended diagnostic work-up for Extra-Pulmonary Tuberculosis (EPTB)?
Similar to PTB, diagnostic bacteriologic confirmation of EPTB includes direct microscopy, TB culture and Xpert® MTB/Rif.
Xpert® MTB/Rif should be preferred over conventional microscopy and culture as initial diagnostic test for CSF specimens from presumptive TB meningitis. (Strong recommendation due to urgency
for rapid diagnosis, very low quality evidence)
Xpert® MTB/Rif may replace usual practice (conventional microscopy, culture or histopathology) for testing lymph node and other selected tissues from presumptive extra-pulmonary TB. (Weak
recommendation, very low quality evidence)
A patient with histological and/or clinical radiologic evidence consistent with active EPTB without laboratory confirmation by direct microscopy, culture or Xpert® MTB/Rif, and decided to be treated by a physician with full course of anti-TB drugs is Clinically Diagnosed EPTB.
The revised definitions and reporting framework for TB (WHO, 2013) classifies EPTB whether bacteriologically confirmed or clinically diagnosed based on results of DSSM, culture or Xpert® MTB/Rif.
Meta-analysis of Xpert® MTB/Rif in diagnosing EPTB as detailed in Table 12 shows consistently high specificity using various non-pulmonary specimens,
TABLE 12 Meta-analysis of the sensitivity and specificity of Xpert® MTB/Rif in diagnosing extra-pulmonary TB by type of extra-pulmonary specimen. (WHO, 2013) SPECIMEN TYPE COMPARISON (NO. OF STUDIES, NO. OF SAMPLES) MEDIAN (%) POOLED SENSITIVITY (POOLED 95% CrL) MEDIAN (%) POOLED SPECIFICITY (POOLED 95% CrL) Lymph node tissue and aspirate
Xpert® MTB/Rif compared against culture
(14 studies, 849 samples) 84.9 (72-92) 92.5 (80-97) Xpert® MTB/Rif compared
against a composite reference standard (5 studies, 1 unpublished)
83.7 (74-90) 99.2 (88-100) CSF Xpert® MTB/Rif compared
against culture
(16 studies, 709 samples) 79.5 (62-90) 98.6 (96-100) Xpert® MTB/Rif compared
against a composite reference standard (6 studies, 512 samples)
55.5 (51-81) 98.8 (95-100) Pleural
fluid Xpert® MTB/Rif compaed against culture
(17 studies, 1385 samples) 43.7 (25-65) 98.1 (95-99) Xpert® MTB/Rif compared
against a composite reference standard (7 studies, 698 samples) 17 (8-34) 99.9 (94-100) Gastric lavage, aspirate
Xpert® MTB/Rif compared against culture
(12 studies, 1258 samples) 83.8 (66-93) 98.1 (92-100) Other tissue
samples Xpert® MTB/Rif compared against culture
(12 studies, 699 samples) 81.2 (68-90) 98.1 (87-100)
Crl, credible interval; the Crl is the Bayesian equivalent of the confidence interval
Reference: Automated real-time nucleic acid amplification technology for rapid and simultaneous detection of tuberculosis and rifampicin resistance: Xpert® MTB/Rif assay for the diagnosis of pulmonary and extra-pulmonary TB in adults and children: Policy Update. Geneva, WHO 2013
lavage and other tissue samples. Because of very high mortality associated with TB meningitis, use of Xpert® MTB/Rif is strongly recommended for testing of CSF. Pleural fluid remains a suboptimal sample for bacterial confirmation; pleural biopsy is a preferred sample. There is still very limited data on samples using ascitic and pericardial fluid, stool, urine or blood. Patients with very high clinical suspicion for EPTB should be treated even if Xpert® MTB/Rif result is negative, specially after adequate further diagnostic testing.
QUESTION 19 What is the role of nucleic acid amplification testing