Rapid Strep Test

What it is

The overwhelming majority of sore throats are viral and get better on their own. A small share are caused by group A streptococcus, and those are worth identifying, because they respond to antibiotics and because untreated strep can occasionally lead to complications elsewhere in the body. The trouble is that a strep throat and a viral one can look the same in the mirror and nearly the same to a clinician. This test exists to settle that question without waiting.

It works by looking for a molecule on the surface of the bacterium rather than by growing anything. The swab is mixed with a reagent that releases the target, and a test strip changes to show whether it is there. That takes minutes instead of the day or two a culture needs. The trade-off is sensitivity: a rapid test that comes back negative does not entirely exclude strep, which is why a negative in a child is often sent on for a culture or a molecular test — and why a second line can appear on the bill.

Why it is done

• To find out whether a sore throat with fever, swollen neck glands or spotted tonsils is caused by group A streptococcus
• To decide whether antibiotics are warranted, rather than prescribing them on appearance alone
• To check household or close contacts of someone with a confirmed case when they develop symptoms
• To evaluate the rash and sore throat of scarlet fever, which is caused by the same bacterium

What to expect

You tip your head back and open wide, and a long cotton-tipped swab is brushed firmly over both tonsils and the back wall of the throat. Firmly is the operative word — a gentle swab misses bacteria. It takes a few seconds, does not hurt, and commonly triggers a gag. The sample is processed in the office or department, and the result is available before you leave. If the result is negative and the clinician still suspects strep, a second swab may be sent to a laboratory, and that result comes back over the following days.

Questions worth asking

• If a backup culture or molecular test is sent after a negative rapid test, that is a separate code from a separate laboratory. Ask whether it was sent and which lab received it.
• Ask whether the outside laboratory is in your network. Patients rarely choose the lab, and it bills independently of the clinic.
• The test is billed on top of the visit itself. Ask whether the office visit and the test appear as separate charges on the estimate.
• In an emergency department this same test carries a facility fee that an office or retail clinic visit does not. Ask what that fee is before being seen if the sore throat is the only reason for the visit.
• If you are uninsured, ask the clinic for its cash price for the test and the visit together — it is frequently lower than the two list prices added up.