Investigations
1st investigations to order
clinical diagnosis
Test
Investigations are only recommended in patients at high risk of complicated disease (pregnant patients and patients with known immunosuppression or conditions involving increased red blood cell (RBC) turnover/destruction) or decreased RBC production).
Result
typical appearance of the classic 'slapped cheek' rash with a lacy, reticular exanthem on the extremities and torso
Investigations to consider
FBC
Test
Recommended to examine for anaemia in the pregnant patient, patients with known immunosuppression or conditions involving increased red blood cell turnover/destruction.
Result
decreased red blood cell count
reticulocyte count
Test
Recommended to evaluate for anaemia in at risk patients.
Result
decreased reticulocyte count
serology
Test
May be useful in the setting of pregnancy or complicated parvovirus B19 infection or in patients at risk for anaemia, but rarely indicated in common erythema infectiosum.
Routine screening during pregnancy is not recommended due to the low risk of seroconversion; testing should be reserved for symptomatic women or those with known exposure.[26]
Patients with aplastic anaemia may have immunoglobulin M (IgM) present at the time of presentation and this finding may persist for 2 to 3 months.[2]
In pregnant women with concern for fetal haemolysis, IgM can be detected in umbilical cord blood more reliably than in maternal serum.[27]
In cases of maternal infection, IgM positivity indicates acute infection and requires fetal monitoring. If both IgM and immunoglobulin G are negative, the patient should be retested after 4 weeks to monitor for seroconversion.[26]
Result
positive IgM antibodies for parvovirus B19
DNA assays
Test
DNA assays (e.g., nucleic acid hybridisation, polymerase chain reaction) are available for acute and persistent parvovirus infection and may be especially helpful in the setting of chronic anaemia, for the detection of virus in amniotic fluid or when ultrasound suggests hydrops fetalis.[2][26]
Result
presence of parvovirus B19 DNA
Use of this content is subject to our disclaimer