Brief Answer:
You will need to get a culture done for that

Detailed Answer:
Hi,

Thanks for the query.

To know if you have streptococcal throat infection, you will have to get a throat swab done and that needs to be cultured to see if there are streptococci.

This is the gold standard test for streptococcal throat infections.

You can also undergo a serology(antibody) test but that is not very accurate.

Hope this answers your question, please feel free to write back if you need further information.

Wishing you good health.

Warm regards

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