Mpox (formerly monkeypox) is diagnosed primarily through a PCR test performed on a swab taken directly from a skin lesion. This test detects viral DNA with roughly 99% sensitivity and near-perfect specificity, making it the gold standard. The process is straightforward: a healthcare provider swabs one or more of your lesions, sends the sample to a lab, and results typically come back in 2 to 4 days.
What Happens During the Test
The core of mpox diagnosis is a skin lesion swab. A provider will use a sterile synthetic swab (not cotton) and firmly rub it across the surface of a lesion to pick up enough viral DNA. They won’t puncture or cut open the lesion. If the rash is in a later stage and crusting over, they’ll collect crust material instead. Ideally, they’ll swab two or three lesions from different parts of your body, or lesions that look different from one another, since this improves the chance of getting a reliable sample.
Each swab goes into its own sterile container, which is then disinfected on the outside before being shipped to the lab. The provider will be wearing full protective equipment throughout the process. From your perspective, the experience is quick and feels similar to any wound swab. There’s no blood draw required for the standard diagnostic test, and no special preparation on your end beforehand.
How PCR Testing Works
The lab runs a type of PCR (polymerase chain reaction) test that amplifies tiny amounts of viral genetic material from your swab until it’s detectable. A pooled analysis of studies found that PCR testing for mpox has a sensitivity of 99% and specificity of essentially 100%. In practical terms, a positive result is almost certainly correct, and a negative result is highly reliable too.
The standard PCR test first checks for orthopoxviruses as a group (the virus family that includes mpox, smallpox, and cowpox). If that comes back positive, further testing can identify the mpox virus specifically. Newer multiplex PCR assays can even distinguish between Clade I and Clade II strains of the virus in a single test, which matters because the two clades differ in severity. Some Clade Ib strains carry genetic deletions that can cause older tests to miss clade-level identification, so laboratories have been developing updated assays that target more stable regions of the virus’s genome.
Clinical Signs That Trigger Testing
Providers don’t test everyone with a rash. A suspected mpox case requires both clinical signs and some link to known exposure. The clinical criteria include a new rash with characteristic lesions, or swollen lymph nodes and fever. The rash is the key feature: mpox lesions progress through distinct stages, starting as flat spots, then raising into bumps, filling with clear fluid, turning cloudy or pus-filled, and finally crusting over. They often appear on the face, hands, feet, genitals, or around the anus.
For a case to be classified as suspected, the clinical signs need to be paired with an epidemiologic link. Higher-risk links include direct contact with someone who has a confirmed infection, or exposure to contaminated materials. Lower-risk links include living in or traveling to a region where mpox is circulating, or contact with certain wild or exotic animals from Africa. The exposure window is 21 days before symptoms appear.
Conditions That Look Similar
Several common infections can mimic mpox, which is one reason testing matters so much. Chickenpox produces a similar-looking rash with fluid-filled blisters, though chickenpox lesions tend to appear in waves (so you’ll see multiple stages at once on the same body area), while mpox lesions in a given area typically progress through stages together. Mpox also causes prominent swollen lymph nodes, which chickenpox usually does not.
When mpox lesions appear on the genitals, they can closely resemble primary syphilis. Some patients have had painless genital ulcers with swollen groin lymph nodes that initially looked like a textbook syphilis case. Herpes simplex is another common lookalike, particularly when lesions cluster in the genital or oral area. Because these conditions overlap visually, laboratory confirmation through PCR is essential rather than relying on appearance alone.
Blood Tests and Antibody Detection
Blood-based antibody testing exists but plays a limited role in diagnosis. The body produces IgM antibodies about 7 days after the rash appears and IgG antibodies around 21 days after onset. This delay makes antibody testing impractical for catching an active infection early, which is when diagnosis matters most for isolation and treatment decisions. Antibody tests are more useful for public health surveillance or confirming past infection after the fact.
Another limitation: antibody tests detect immune responses to orthopoxviruses broadly, not mpox specifically. Someone who received a smallpox vaccine years ago could test positive for orthopoxvirus antibodies without ever having had mpox. For these reasons, PCR from a lesion swab remains the primary and most reliable diagnostic tool.
How Long Results Take
Once your specimen reaches the lab, results are typically available in 2 to 4 days. Testing is performed at public health laboratories and some commercial labs. The specimens are handled in specialized biosafety facilities, with vaccinated lab staff working at biosafety level 2 and unvaccinated staff using the higher-containment biosafety level 3 setup. Any work involving live virus culture requires level 3 containment regardless of vaccination status.
While you wait for results, your provider will likely recommend isolating as if the test were positive. This means covering your lesions, avoiding skin-to-skin contact with others, and not sharing bedding, towels, or clothing. If the result comes back negative but your symptoms still look suspicious, your provider may recommend retesting, particularly if the initial swab was collected very early in the rash’s development when viral load may be lower.