Investigations

1st investigations to order

reverse transcriptase-polymerase chain reaction (RT-PCR)

Test
Result
Test

Should be ordered in all patients with suspected RVF infection.[12] Live virus or nucleic acids may be detected in blood during the early phase of illness, or in postmortem tissue.

RT-PCR may not be readily available in all clinic and laboratory facilities in Rift Valley fever virus (RVFV)-endemic areas. Sample testing can be coordinated with specialised laboratories, such as the Centers for Disease Control and Prevention (CDC) in the US.

Result

positive for RVFV RNA

serum IgM or IgG detection with ELISA

Test
Result
Test

Typically, IgM can be detected during early stages of acute illness, shortly after the initial onset of symptoms (approximately 5 days after illness onset). IgG can typically be detected (approximately 7-10 days after illness onset) as a measure of previous exposure and persists for life; therefore it may not be representative of the causative agent for current febrile illness. Genus-specific cross-reactivity is common with ELISAs.[12]

Timepoints for IgM and IgG are dependent on the infection and human immune response, and can vary by patient. Approximate onset has been generalised comparatively with other mosquito-borne viruses that are endemic in overlapping regions.

ELISA assays may not be readily available in all clinic and laboratory facilities in RVFV-endemic areas. Sample testing can be coordinated with specialised laboratories, such as the CDC in the US.

Result

positive for anti-RVFV IgM or IgG antibodies

FBC

Test
Result
Test

High leukocyte count may be associated with higher mortality risk.[41]

Result

leukocyte count indicative of acute illness

serum electrolytes

Test
Result
Test

Used to physiologically confirm the experience of symptoms commonly associated with RVF, such as dehydration from fever and loss of appetite; kidney and liver function; or fluid, electrolyte, or pH imbalance as an indicator for the onset of haemorrhagic fever.[41][51][55]

Result

may be abnormal

LFTs

Test
Result
Test

Hepatitis may be indicative of severe disease.[55][56][57] One study found elevated liver enzymes in 98% of patients surveyed.[41]

Result

ALT:AST ratio and bilirubin may be elevated

Investigations to consider

coagulation studies

Test
Result
Test

If signs or symptoms of bleeding occur, or if LFTs are elevated, coagulation studies should be ordered to ensure liver function and determine risk of bleeding.[55][56][57]

Result

prolonged PT or activated PTT, elevated D-dimer level (if bleeding manifestations)

serum creatinine and urea

Test
Result
Test

May indicate acute kidney injury. Especially useful in patients with diarrhoea and vomiting.[55][58]

Result

may be elevated

creatine phosphokinase (CPK)

Test
Result
Test

CPK levels more than twice the upper limit of the normal range may indicate systematic muscular stress.[55]

Result

may be elevated

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