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Published on: April 6, 2021
In vitro comparison of four rapid antigen tests for group A streptococcus detection
Arlo Upton1, Cathy Lowe, Joanna Stewart
1Microbiology, Labtests, 37-41 Carbine Road, Mt Wellington, Auckland 1060, New Zealand. arlo.upton@labtests.co.nz.
Aims:
To examine the analytical sensitivity of four rapid antigen tests (RADT) for detection of group A streptococcus (GAS).
Methods:
The sensitivities of four RADT kits to detect clinical and reference strains of GAS at different dilutions were compared. Test results were read by two people, and differences in interpretation were settled by a third reader.
Results:
A total of 697 tests were performed. For all kits, detection increased with increasing colony counts of GAS. One kit [ulti med Products, Deutschland, GmbH (UM)] was found to have the highest sensitivity, although there was no significant difference between it and one other kit (Testpack Plus). All kits were only faintly positive or negative at low colony counts.
Conclusions:
The sensitivity of RADT for detecting GAS is related to inoculum size and the faint appearance of a positive test at low colony counts contributes to inter-observer variability. Sore throats with low colony counts have been shown to be clinically relevant.
