Most upper respiratory infections are diagnosed through a physical exam and your symptom history, not a single definitive test. Because the vast majority of URIs are caused by viruses that resolve on their own, your doctor’s main goal is usually to rule out bacterial infections like strep throat or complications like sinusitis, rather than to identify the exact virus making you sick. When specific testing is needed, options range from rapid swabs you can do at home to comprehensive lab panels that screen for more than 20 pathogens at once.
What Happens During a Clinical Exam
A doctor can diagnose most upper respiratory infections in the exam room without ordering any tests. They’ll look inside your nose for redness and swelling of the nasal lining, check the back of your throat for inflammation or white patches, and feel along the front of your neck for swollen lymph nodes. These findings, combined with your symptoms and how long you’ve been sick, are usually enough to confirm a URI and guide the next steps.
The physical exam also helps distinguish a straightforward cold from something that needs more investigation. White patches on the tonsils, for example, appear in about half of adenovirus infections but also raise suspicion for strep throat. A high fever with no cough points more toward a bacterial cause than a viral one. Your doctor is essentially sorting your infection into categories: likely viral (no further testing needed), possibly bacterial (testing recommended), or potentially complicated (imaging or blood work warranted).
Rapid Tests You Can Use at Home
Over-the-counter rapid antigen tests are now available for several common respiratory viruses. The most widely used home kits test for COVID-19, and newer combination tests can detect influenza A, influenza B, and RSV alongside SARS-CoV-2 in a single nasal swab. These tests give results in about 15 minutes.
The tradeoff with rapid antigen tests is sensitivity. Compared to the gold-standard PCR tests, rapid antigen tests catch roughly 47% of infections when measured against PCR results. They’re much better at confirming you’re contagious, though: when compared against viral culture (which measures whether live, transmissible virus is present), sensitivity jumps to about 80%. In practical terms, a positive rapid test is highly reliable, but a negative result doesn’t guarantee you’re in the clear, especially early in the illness.
Timing matters significantly. Viral loads in the upper respiratory tract peak right around symptom onset and stay high through the first four days of illness. Nasopharyngeal samples taken in that zero-to-four-day window detect infection about 89% of the time, dropping to 54% after 10 to 14 days. For the most accurate result, test as soon as symptoms start rather than waiting to see if you get worse.
Strep Throat Screening
Strep throat is the main bacterial infection doctors screen for during a URI visit, because it requires antibiotics and can lead to complications if untreated. Clinicians use a scoring system based on four criteria: fever of 38°C (100.4°F) or higher, absence of cough, swollen lymph nodes at the front of the neck, and white patches or swelling on the tonsils. Each criterion adds one point, producing a score from 0 to 4.
If you score below 3, strep is unlikely and testing is generally skipped. A score of 3 or 4 means a rapid strep test or throat culture is recommended to confirm the diagnosis before starting antibiotics. The rapid strep test involves swabbing the back of your throat and produces results in minutes. If that comes back negative but your doctor still suspects strep, a traditional throat culture (sent to a lab, results in one to two days) can catch infections the rapid test misses.
PCR Panels for Identifying Specific Viruses
When your doctor needs to know exactly which pathogen is causing your illness, they can order a multiplex PCR respiratory panel. This is a single nasopharyngeal swab processed in a lab that screens for a broad range of pathogens simultaneously. A standard panel covers influenza A (including multiple subtypes), influenza B, RSV, SARS-CoV-2, four types of common coronavirus, adenovirus, rhinovirus/enterovirus, parainfluenza viruses 1 through 4, and human metapneumovirus. It also picks up several bacterial causes: the bacteria responsible for whooping cough, as well as two atypical bacteria that can cause walking pneumonia.
These panels are more common in hospital settings, for patients with severe symptoms, or when knowing the specific virus changes treatment decisions (such as prescribing antiviral medication for influenza). They’re significantly more sensitive than rapid antigen tests because they amplify tiny amounts of genetic material to detect the pathogen. Results typically come back within 24 hours. Your doctor is less likely to order one for a mild cold that’s following a typical course.
Blood Tests for Bacterial vs. Viral Infections
In some cases, particularly when a URI seems to be progressing into a lower respiratory infection or pneumonia, blood tests can help determine whether bacteria are involved. Two inflammatory markers are commonly used. Procalcitonin, a protein that rises sharply during bacterial infections, performs best at distinguishing bacterial from viral causes: at a threshold of 1.5 ng/mL, it correctly identifies bacterial involvement about 56% of the time while correctly ruling it out 84% of the time. C-reactive protein (CRP), another inflammation marker, is somewhat less precise on its own, with 69% sensitivity and 63% specificity at a cutoff of 10 mg/dL.
When both markers are used together, specificity climbs to 93%, meaning a negative result on both tests makes bacterial co-infection very unlikely. These blood draws aren’t routine for a standard URI. They’re reserved for situations where the stakes of missing a bacterial infection are higher, such as in patients with worsening symptoms, weakened immune systems, or infections that aren’t improving as expected.
When Imaging Comes Into Play
Plain URIs don’t require imaging. A CT scan of the sinuses enters the picture only under specific circumstances: when symptoms of sinusitis persist beyond 12 weeks despite treatment, or when red-flag signs suggest a serious complication. Those red flags include swelling around the eye socket, severe headache, altered mental status, neurological changes, or signs of meningeal irritation. These symptoms can indicate that an infection has spread beyond the sinuses into surrounding structures, potentially causing periorbital cellulitis, brain abscess, or other dangerous complications.
Standard X-rays and ultrasound of the sinuses are not considered reliable enough to guide diagnosis and are generally not recommended. If your doctor suspects complicated sinusitis, a CT scan is the imaging method of choice.
Telling a URI Apart From Allergies
The symptoms that bring people in for URI testing often overlap heavily with allergic rhinitis: nasal congestion, runny nose, and sneezing appear in both conditions. The distinguishing features of a true infection are the “extra” symptoms that allergies rarely cause. Cough, general fatigue or malaise, sore throat, fever or chills, and headache alongside nasal symptoms point toward an infectious cause. If your congestion comes with itchy eyes, follows a seasonal pattern, or has been going on for weeks without fever or body aches, allergies are the more likely explanation, and antiviral or antibiotic testing would not be useful.