Investigations
1st investigations to order
reverse transcription-polymerase chain reaction (RT-PCR)
Test
Should be ordered in all patients with suspected Lassa fever while the patient is in isolation and personal protective equipment is used.[2][9]
Consider repeating after 24 hours if initial results are negative and clinical suspicion remains high.
Specimens should be sent to a laboratory that is suitably equipped to handle biosafety level 4 pathogens; however, this may not be available in endemic countries.
Result
positive for Lassa virus RNA
serology
Test
Lassa fever can be diagnosed by IgM ELISA.[2][9][32] IgM ELISA has demonstrated 88% sensitivity and 90% specificity for acute infection.[32]
Consider repeating after 24 hours if initial results are negative and clinical suspicion remains high.
Specimens should be sent to a laboratory that is suitably equipped to handle biosafety level 4 pathogens; however, this may not be available in endemic countries.
Newer ELISAs and rapid diagnostic tests have been developed which are able to detect IgG/IgM and antigen.[1]
Result
positive for Lassa virus IgM antibodies
rapid diagnostic lateral flow assay
Test
The ReLASV® Antigen Rapid Test is the only rapid diagnostic test for Lassa fever. It is a dipstick-style lateral flow immunoassay that detects Lassa virus antibodies and antigens in blood from a single finger prick. Performance against PCR has demonstrated sensitivity of 95%.[12] If results are negative, results from RT-PCR or serology should be sought for diagnostic confirmation.
Result
positive for Lassa virus antigen or antibodies
rapid diagnostic test for malaria
Test
Malaria is usually co-endemic with Lassa fever, and can be difficult to distinguish from Lassa fever; therefore, a rapid diagnostic test for malaria should be carried out immediately.
Co-infection is unusual, though not impossible, and consideration should be given to testing the samples for Lassa fever whilst treating malaria infection.
Result
negative (may be positive if co-infection)
blood culture for typhoid
Test
Typhoid is usually co-endemic with Lassa fever, and can be difficult to distinguish from Lassa fever; therefore, testing for typhoid is recommended.
No reliable rapid diagnostic tests are available, and blood culture remains the main diagnostic method for typhoid fever. The Widal test is neither sensitive nor specific and is not routinely recommended, but is often performed in endemic settings.
Co-infection is unusual, though not impossible, and consideration should be given to testing the samples for Lassa fever whilst treating typhoid infection.
Specimens should be sent to a laboratory that is suitably equipped to handle biosafety level 4 pathogens; however, this may not be available in endemic countries.
Result
negative (may be positive if co-infection)
Investigations to consider
renal function
Test
Moderately elevated creatinine has been seen in patients with Lassa fever, potentially indicating dehydration or damage from elevated creatine kinase.[4]
Result
elevated urea and creatinine
serum electrolytes
Test
Especially useful in patients with diarrhoea and vomiting, and can be used to guide correction of electrolytes and fluid replacement.
Result
may be deranged
blood lactate/ABG
Test
Blood lactate, arterial or venous pH, and bicarbonate can be used to determine tissue hypoperfusion and guide fluid management.
Result
metabolic acidosis
FBC
Test
Elevated haematocrit is indicative of dehydration. Thrombocytopenia has been reported.[33]
Result
elevated haematocrit; thrombocytopenia
coagulation studies
Test
Should be performed and abnormalities corrected as necessary.
Result
coagulopathy
liver function tests
Test
Elevated alanine aminotransferase (ALT) has been noted and is associated with worse outcome.[34]
Result
elevated ALT
chest x-ray
Test
Should be performed to look for pleural or pericardial effusion.
Result
may reveal pleural effusion or pericardial effusion
urinalysis
Test
Should be performed to screen for proteinuria.
Result
proteinuria
blood cultures
Test
Blood cultures may be helpful in the identification of other causes of sepsis (e.g., deep abdominal infection, upper urinary tract infection, endocarditis, or discitis). Bacterial sepsis with an unclear origin is a common presentation in developing countries.
Result
negative
lumbar puncture
Test
May be considered in patients presenting with altered Glasgow Coma Scale or signs of encephalopathy as Lassa virus has been detected in cerebrospinal fluid (CSF).[30]
Not routinely recommended due to risk of transmission to healthcare workers during the procedure. It can also be particularly difficult and dangerous in encephalopathic patients who are in a state of confusion.
Encephalopathy is quite common among symptomatic patients who present after more than 6 days of symptoms; however, detection of Lassa virus RNA in CSF has been rarely reported, as lumbar puncture is rarely performed in these patients.[30]
Result
positive for Lassa virus RNA (detected by PCR)
abdominal ultrasound
Test
Has been suggested for the investigation of intraperitoneal fluid and pericardial effusion.[18]
Result
may reveal presence of intraperitoneal fluid or pericardial effusion
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