Investigations

1st investigations to order

polymerase chain reaction (PCR)

Test
Result
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, possible, or probable case.[170] The decision to test should be based on both clinical and epidemiological 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. NAAT can be generic to Orthopoxvirus or specific to monkeypox virus (preferable).[170][171][172][173] Sequencing is useful to determine virus clade and to understand epidemiology.

Caution is required when interpreting a single test result in patients with a low pretest probability of infection (e.g., lack of epidemiological link, non-MSM [men who have sex with men] populations, signs/symptoms inconsistent with mpox) due to the risk of a false-positive result.[175] A positive test for Orthopoxvirus or monkeypox virus DNA in a person without epidemiological criteria or known risk factors should be verified by repeat testing and/or confirmatory testing, and other possible causes of rash considered.[176] 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 non-infectious specimens.[175][177]

The recommended specimen type is skin lesion material, including swabs of lesion exudate, roofs from more than one lesion, or lesion crusts.[170][172]​ Skin lesion swabs are the most effective means of detecting monkeypox virus DNA using PCR.[178][179]​ 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, ethylenediamine tetra-acetic acid (EDTA) blood, or urine. 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.[171] 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.[150][180]​ 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.[181][182][183]

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 virological 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 co-infection is present.

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

FBC

Test
Result
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

Test
Result
Test

Order in all patients with suspected infection.

Small studies have found that low urea was common during illness.[1]

Low urea may be a sign of severe or complicated disease.[1]

Result

may show low urea or other derangements

LFTs

Test
Result
Test

Order in all patients with suspected infection.

Small studies have found that elevated transaminases and hypoalbuminaemia were common during illness.[1][31]​ Elevated transaminases and hypoalbuminaemia may be signs of severe or complicated disease.[1] Severe hepatitis has been reported in patients with hepatitis co-infection.[191]

Result

may show elevated transaminases, hypoalbuminaemia

sexually transmitted infection tests

Test
Result
Test

Test all sexually active adults and adolescents for HIV infection and other STIs.[101]

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. Co-infections are possible, and the presence of an STI does not rule out mpox.[138]

Result

variable (depends on the infection present)

Investigations to consider

CT abdomen/pelvis

Test
Result
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 non-enhancing hypoattenuated zones due to intramural ulcers. Additional findings may include perirectal fat infiltration, presacral eodema, ascites, and an increased number of small inguinal lymph nodes.[184]

Result

anorectal mural thickening

serology

Test
Result
Test

Serology is not currently recommended by the World Health Organization (WHO) for diagnosis. Serology (paired serum samples collected at least 21 days apart, with the first collected during the first week of illness) can aid diagnosis if tested samples yield inconclusive results. Recent vaccination may interfere with serological testing.[170] However, the WHO and the US Centers for Disease Control and Prevention include serological testing as an option for testing in their case definitions.[81][141] See Criteria.

Result

positive

blood culture

Test
Result
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 bacteraemia

malaria antigen test

Test
Result
Test

Order in all patients with suspected infection if there is a recent history of travel to a malaria-endemic area.

Always rule out co-infection 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 organised as per local policies.

Result

negative; may be positive if co-infection

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