Tests
1st tests to order
reverse transcriptase-polymerase chain reaction (RT-PCR)
Test
Should be ordered in all patients with suspected infection while the patient is in isolation.[110]
Returns result 24-48 hours before ELISA testing.
Several different commercial PCR kits are available with varying sensitivity, specificity, and limits of detection.[111]
In Western settings, the test may only be available in regional or national laboratories that have category 4 facilities.[7] In epidemic settings and some countries, category 4 laboratories are set up locally and results are available 4 hours after the sample has arrived.
Viral RNA can be detected in the patient’s blood by RT-PCR from day 3 up to days 6-17 of symptom onset. A positive PCR result implies that the patient is potentially infective, particularly if he or she has active diarrhea, vomiting, or bleeding.
If negative, the test should be repeated within 48 hours since viral load is low and can be undetectable early in the course of the illness. Negative tests should be repeated to rule out a diagnosis if it is strongly suspected (or confirm resolution of infection).[110]
Higher viral load correlates with adverse outcome and increased mortality.[20][21][22][70][94][110][112]
Result
positive for orthoebolavirus RNA
malaria investigations
Test
Giemsa-stained thick and thin blood smears and rapid diagnostic tests are the tests of choice for malaria screening.
A negative result makes Ebola disease more likely in the appropriate epidemiologic context; however, coinfection with malaria was seen in up to 5% of patients in West Africa during the 2014 outbreak, so the possibility of dual infection should be considered in all patients.[94]
Result
negative (may be positive if dual infection)
Tests to consider
serum electrolyte levels
Test
Important test to order (if available) in areas where other investigations are limited.
May indicate acute kidney injury.[114]
Especially useful in patients with diarrhea and vomiting.
Hypokalemia or hyperkalemia, due to vomiting and diarrhea or acute kidney injury, was seen in approximately 33% of cases in the 2014 outbreak.[94]
Hypocalcemia has been associated with fatal infection.[16]
Useful to guide correction of electrolytes and fluid replacement.
Result
may be abnormal
BUN/serum creatinine
blood lactate
Test
Important test to order (if available) in areas where other investigations are limited.
Elevated lactate is a marker of tissue hypoperfusion and is an indicator of shock. It is useful in acutely ill patients with signs of sepsis to identify the degree of systemic hypoperfusion and to guide fluid resuscitation.[115]
Elevated lactate was one indicator of gram-negative sepsis at day 15 in a patient treated in Germany.[45]
Result
variable
ABG
Test
Arterial or venous blood pH and bicarbonate are useful in acutely ill patients with signs of sepsis to identify the degree of systemic hypoperfusion and guide fluid resuscitation.[115]
Result
variable
CBC
Test
Decrease in platelet count and marked lymphopenia can be seen in the initial stages of infection; however, this is not diagnostic. Often followed by neutrophil leukocytosis in the later stages of patients who eventually recover, along with normalization of thrombocytopenia. Leukocytosis may persist and show immature forms.[16]
Patients with severe disease may show a progressive decline in platelet count as a manifestation of disseminated intravascular coagulation (DIC).
Decreased hemoglobin levels were reported in 24% of patients in the 2014 outbreak, and have been associated with bleeding in previous outbreaks.[16][94]
Result
thrombocytopenia, marked lymphopenia; decreased hemoglobin (if bleeding manifestations)
coagulation studies
Test
Prolonged prothrombin time (PT) or activated partial thromboplastin time (aPTT) is associated with more severe infection and bleeding manifestations such as DIC.
Patients with fatal infection have been found to have D-dimer levels four-fold higher on days 6-8 of infection compared with patients who survive.[116]
Result
prolonged PT or aPTT, elevated D-dimer level (if bleeding manifestations)
urinalysis
Test
Hematuria or proteinuria may be seen in severe disease.[16]
Oliguria that does not respond to fluid resuscitation is a poor prognostic sign.
Result
may show hematuria or proteinuria
LFTs
Test
Both ALT and AST are usually elevated; however, most studies show that AST rises out of proportion to ALT, and this is more suggestive of systemic tissue damage rather than hepatocellular injury.[94]
AST:ALT ratio peaked at 15:1 on days 6-8 of infection in fatal cases when compared with nonfatal cases, which had a peak of 5:1.[5][16][116]
Bilirubin, GGT, and ALP are often slightly elevated. Highly elevated ALT and severe jaundice suggests an alternative diagnosis (e.g., viral hepatitis).
Result
high AST:ALT ratio; bilirubin, GGT, and ALP may be slightly elevated
serum amylase level
Test
Elevated levels have been reported in several studies and indicates the presence of pancreatitis, an indicator of severe infection.[16]
Result
may be elevated
blood cultures
Test
Negative blood cultures are helpful as they rule out other nonviral infectious causes (e.g., sepsis, enteric fever).
Gram-negative bacteremia, presumably from gut translocation, has been identified as a complication of the disease course in two patients.[45][117] However, a study in Sierra Leone where blood cultures were taken from patients on admission to an Ebola treatment center found that only one of the 22 cultures was positive with a presumed contaminant.[118]
Therefore, blood should be collected for culture at baseline and/or at the time of the onset of gastrointestinal symptoms or other clinical deterioration.
Result
negative
serum blood glucose
antigen-capture enzyme-linked immunosorbent assay (ELISA)
Test
Useful diagnostic test with high specificity; however, it is not universally available. Can be used to confirm the diagnosis along with a positive RT-PCR result.
Most likely to give a positive result from day 3 until day 6 of infection, and can give widely variable results from days 7-16.[49]
Result
positive for orthoebolavirus antibodies
IgM and IgG antibodies
Test
Useful in later stages of the infection.
IgM antibodies can appear in serum as early as day 2 post infection, but can give variable results up to day 9. They become negative between 30 and 168 days after symptom onset. IgG response develops between day 6-18 and can persist for several years.[49]
A positive IgM or a rising IgG titer is strong evidence for recent infection.
Result
positive
chest x-ray
Test
Useful in patients with respiratory symptoms.
Pulmonary infiltrates are not typical of infection and suggest an alternative (or comorbid) diagnosis.
May be difficult to arrange in an isolation unit and should only be ordered judiciously to avoid contamination.[119]
Result
negative
Emerging tests
rapid diagnostic tests
Test
Rapid PCR testing remains a major hurdle for effective, targeted isolation of affected patients. Current tests take an average of 4 hours to perform with a fully equipped laboratory close at hand, but results may take several days to arrive in remote areas. This means that, until they are confirmed negative, patients with febrile illnesses other than Ebola disease are confined to isolation and often unwittingly exposed to the virus.
Rapid bedside tests can, therefore, make a very significant contribution to infection control in treatment centers.
Several different technologies are being evaluated by WHO for use in field conditions. These include numerous RT-PCR-based assays that have been made simpler to use with a shorter turnaround time of <1 hour. The WHO has listed ReEBOV™ Antigen Rapid Test Kit for potential use; however, it currently only recommends its use in special situations. WHO: interim guidance on the use of rapid Ebola antigen detection tests Opens in new window Other test kits have also been granted emergency use authorization by the WHO.
The alternatives are ELISA-based antigen-detection assays that could be quicker and simpler with the possible advantage of only needing a drop of blood. Their major disadvantage is a reduced sensitivity, particularly in the initial stages of illness.[120]
Nanopore technology may allow rapid detection and sequencing in the presence of very low levels of virus, and can potentially be deployed using a pocket-sized detection kit.[122][123][124]
A GeneXpert® diagnostic tool (Xpert® Ebola) has been trialled in the field, and is an automated cartridge-based system that requires minimal laboratory skill. An inactivated sample is placed into a single-use cartridge, which is then entered into the enclosed machine. Sample preparation, nucleic acid amplification and detection, and production of a result are automated processes minimizing staff training requirements, risk of infection, and cross contamination.[125]
The Food and Drug Administration has approved a rapid, single-use test for the detection of Orthoebolavirus zairense. It is the second rapid antigen fingerstick test available under an emergency use authorization, but is the first that uses a portable battery-operated reader which can provide results outside of laboratories.[128] It has also approved the single-use OraQuick® Ebola Rapid Antigen Test to detect virus antigens in human blood from certain living individuals, as well as samples from certain recently deceased individuals suspected to have died from Ebola disease (cadaveric oral fluid). It is the first rapid diagnostic test to be marketed in the US, and provides a rapid, presumptive diagnosis that must be later confirmed.[129]
The pooled sensitivity and specificity of rapid tests has been reported as 86% and 95%, respectively.[130]
This is an evolving field and different kits are approved according to the country and settings in which they are to be deployed.
Result
positive for orthoebolavirus
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