Diagnostic accuracy of a commercial cross priming amplification diagnostic kit in smear negative sputum

Date of Award


Document Type


Degree Name

Master of Medicine (MMed)


Pathology (East Africa)


Background: The diagnosis of smear negative tuberculosis remains a major obstacle to global control of tuberculosis (TB), especially in resource limited settings. Several nucleic acid based diagnostic tests have been developed to improve diagnosis. The polymerase chain reaction has been the benchmark for nucleic acid amplification; many novel alternatives have been developed for the amplification and detection of nucleic acid sequences.

Objective: The study aimed to determine the diagnostic accuracy of Cross Priming Amplification technology using the Ustar TB Isothermal Amplification Diagnostic (IAD) Kit (Ustar Biotech, Hangzhou, China) in smear negative sputum.

Methods: 159 unconcentrated sputum samples negative by direct Ziehl-Neelsen staining referred to the National Central Reference Lab in Nairobi were subjected to both the Ustar TB Isothermal Amplification Diagnostic Kit and culture. The reference standard was TB culture.

Results: When tested on Ziehl-Neelsen negative smear sputum, the IAD assay was found to have a sensitivity of 75% (60-86%; 95% CI); Positive Predictive Value (PPV) of 84% (71-94%; 95% CI) and Diagnostic Odds Ratio of 42.18 (15.65-113.69; 95% CI). The specificity of the assay was 94% (87-97%; 95% CI).

Conclusion: The assay demonstrated good sensitivity and moderate specificity in detecting mycobacterium tuberculosis in smear negative specimen, the requirements for a clean room for the DNA extraction procedure, a high speed centrifuge and biological safety chamber may limit the applicability of this technique in resource limited settings.

This document is available in the relevant AKU library