Tests
1st tests to order
polymerase chain reaction (PCR)
Test
Testing should be conducted in patients with suspected infection as soon as possible.[1] Offer testing to any person who meets the case definition for a suspected or probable case.[214] The decision to test should be based on both clinical and epidemiologic factors, linked to an assessment of the likelihood of infection. Patients should remain in isolation while their test result is pending.
Testing is available at regional public health laboratories. There are currently no commercial assays available.
Nucleic acid amplification testing (NAAT), using real-time PCR or conventional PCR, is the preferred laboratory test given its accuracy and sensitivity. It can be used alone or in combination with sequencing for clade determination. NAAT can be generic to Orthopoxvirus or specific to monkeypox virus (preferable). Positive detection using an Orthopoxvirus PCR assay should be followed by monkeypox virus PCR and/or sequencing or detection to confirm the diagnosis. If clade-specific NAATs fail to detect mpox, subsequent sequencing may be used for clade determination and genetic characterization.[214][215][216][217] Sequencing is useful to determine virus clade and to understand epidemiology. Following a cluster of sexually transmitted clade I infections identified in 2023 (due to the newly identified clade Ib variant), clade confirmation is recommended in all individuals who test positive for mpox.[215][222]
Caution is required when interpreting a single test result in patients with a low pretest probability of infection (e.g., lack of epidemiologic link, non-MSM [men who have sex with men] populations, signs/symptoms inconsistent with mpox) due to the risk of a false-positive result.[219] A positive test for Orthopoxvirus or monkeypox virus DNA in a person without epidemiologic criteria or known risk factors should be verified by repeat testing and/or confirmatory testing, and other possible causes of rash considered.[220] Repeat testing (re-extraction and retesting of the specimen) is recommended in patients with high real-time (RT)-PCR cycle threshold values (i.e., ≥34), as this indicates a low level of viral DNA and poorly- or noninfectious specimens.[219][221]
The recommended specimen type is skin lesion material, including swabs of lesion exudate, roofs from more than one lesion, or lesion crusts.[214][215][216] Skin lesion swabs are the most effective means of detecting monkeypox virus DNA using PCR.[223][224] Aspiration or unroofing of lesions before swabbing is not necessary (or recommended) due to the risk for sharps injury. Specimen type may vary depending on the phase of the rash. The reference laboratory may also ask for an oropharyngeal swab, anorectal swab, ethylenediamine tetra-acetic acid (EDTA) blood, or urine. Alternative specimen types (e.g., oropharyngeal swabs) can be collected from contacts of suspected or confirmed cases but who have no visible skin or mucosal lesions. However, they may lack sensitivity in presymptomatic cases, and testing should be repeated on lesion material if a rash or mucosal lesions develop.[214] Oropharyngeal swabs are recommended for high-risk contacts of a confirmed or highly probable case who have developed systemic symptoms but do not have a rash or lesion for sampling. A throat swab should also be taken if there are pharyngeal lesions.[215] However, viral load is higher in lesion swabs than in pharyngeal specimens, and oropharyngeal swabs are known to be unreliable standalone specimen types for primary diagnosis.[191][225] There are limited clinical data to support the use of sample types other than swab samples taken directly from a lesion (e.g., blood, saliva). Testing samples not taken from a lesion may lead to false positive results.[226][227][228]
Collect, label, package, and send specimens according to local or national protocols. Notify the laboratory of the possibility of mpox prior to sending specimens. There are local protocols in place for the safe handling of these specimens in the laboratory and onward transport of virologic materials to the reference laboratory. Package samples for testing for other infections separately.
Testing the sample for varicella zoster virus should automatically be performed by the reference laboratory when undertaking PCR for poxviral DNA. It may be positive for varicella zoster virus DNA if coinfection is present.
Point-of-care tests may be available in some countries.
UKHSA: mpox (monkeypox) - diagnostic testing Opens in new window
CDC: guidelines for collecting and handling specimens for mpox testing Opens in new window
Result
positive for monkeypox or Orthopoxvirus virus DNA
CBC
Test
Order in all patients with suspected infection.
Small studies have found that leukocytosis was common, and lymphocytosis and thrombocytopenia were seen in more than one third of patients during illness.[1]
Leukocytosis and thrombocytopenia may be signs of severe or complicated disease.[1]
Result
may show leukocytosis, lymphocytosis, thrombocytopenia
urea and electrolytes
LFTs
Test
Order in all patients with suspected infection.
Small studies have found that elevated transaminases and hypoalbuminemia were common during illness.[1][44] Elevated transaminases and hypoalbuminemia may be signs of severe or complicated disease.[1] Severe hepatitis has been reported in patients with hepatitis coinfection.[238]
Result
may show elevated transaminases, hypoalbuminemia
sexually transmitted infection tests
Test
Test all sexually active adults and adolescents for HIV infection and other STIs.[182]
The clinical features of mpox may easily be confused with an STI. Therefore, it is important to comprehensively evaluate patients presenting with genital or perianal ulcers for STIs. Coinfections are possible, and the presence of an STI does not rule out mpox.
Result
variable (depends on the infection present)
Tests to consider
CT abdomen/pelvis
Test
Consider a CT scan of the abdomen/pelvis in patients with severe anorectal proctitis.
Contrast-enhanced CT may reveal circumferential anorectal mural thickening with broad discrete nonenhancing hypoattenuated zones due to intramural ulcers. Additional findings may include perirectal fat infiltration, presacral edema, ascites, and an increased number of small inguinal lymph nodes.[229] Mean transverse rectal wall thickness was greater among patients with HIV in one study.[239]
Result
anorectal mural thickening
serology
Test
Serology is not currently recommended by the World Health Organization (WHO) for diagnosis. Serology (paired serum samples collected at least 14 to 21 days apart, with the first collected during the first week of illness) can aid diagnosis if tested samples yield inconclusive results with molecular testing. Recent vaccination may interfere with serologic testing.[214]
Result
positive
blood culture
Test
Order while the patient is in isolation and prior to antibiotic therapy, if there is suspicion of bacterial superinfection of cutaneous lesions or bacterial infection in a very sick patient.
Result
may show bacteremia
malaria antigen test
Test
Order in all patients with suspected infection if there is a recent history of travel to a malaria-endemic area.
Always rule out coinfection with malaria in any febrile patient who has been to a malaria-endemic area, especially in the 3 weeks prior to the onset of fever.
An antigen detection test poses less of an infection hazard to laboratory staff than preparation of thick and thin films. The laboratory must first be notified of the risk of mpox and secure transportation of specimens organized as per local policies.
Result
negative; may be positive if coinfection
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