From the Guidelines
Blood tests for diagnosing parasitic infections in the blood include microscopy of Giemsa-stained thick and thin blood films, serological tests, and molecular tests like PCR, with the choice of test depending on the specific parasite suspected, as outlined in the 2018 update by the Infectious Diseases Society of America and the American Society for Microbiology 1.
Key Diagnostic Tests
- Microscopy of Giemsa-stained thick and thin blood films is the gold standard for diagnosing malaria and babesiosis, with thick smears detecting infection and thin smears identifying the specific Plasmodium species 1.
- Serological tests, such as ELISA, IFA, and PCR, detect antibodies against parasites and can identify parasite DNA, with molecular tests like PCR being highly sensitive for detecting low levels of parasites 1.
- Specialized tests exist for specific parasites like Chagas disease or leishmaniasis, and testing is particularly important for those with travel history to endemic regions, unexplained eosinophilia, or persistent symptoms unresponsive to standard treatments 1.
Importance of Testing
- Accurate diagnosis is crucial for effective treatment and prevention of complications, as many parasitic infections present with nonspecific symptoms like fever, fatigue, and anemia 1.
- Testing should be guided by clinical suspicion and epidemiological history, with consideration of the specific parasite suspected and the available diagnostic tests 1.
Recent Guidelines
- The 2018 update by the Infectious Diseases Society of America and the American Society for Microbiology provides a comprehensive guide to the diagnosis of parasitic infections, including the use of microscopy, serology, and molecular tests 1.
- More recent studies, such as those published in 2024, highlight the importance of accurate diagnosis and treatment of malaria in non-endemic settings, with a focus on the use of oral artemisinin-based combination therapy (ACT) and intravenous artesunate for severe cases 1.
From the Research
Blood Tests for Parasitic Infections
The following blood tests can be used to diagnose parasitic infections:
- Giemsa-stained thin blood smears to detect Plasmodium species, such as Plasmodium falciparum, Plasmodium ovale, Plasmodium vivax, and Plasmodium malaria 2
- Peripheral blood smear (PBS) to detect microfilaria, which may not always be associated with eosinophilia 3
- PCR (polymerase chain reaction) to detect Babesia microti parasitemia, which is as sensitive and specific as Giemsa-stained blood smears and inoculation of hamsters 4
- Serological tests, such as indirect hemagglutination (IHA), indirect fluorescence antibody (IFA), enzyme-linked immunosorbent assay (EIA), and Western blot (WB), to detect antibodies against various parasites, including Toxocara, Trichinella, Echinococcus, Cysticercus, Toxoplasma, and Schistosoma 5
Limitations of Blood Tests
It is essential to note that:
- Manual microscopy may not be a trustworthy screening technique when performed by non-experts 2
- Serological results must be interpreted in consideration of the clinical picture of the patient and confirmed possibly by finding the parasite or its genome 5
- The presence of specific antibodies can reveal an acquired infection, but not necessarily a disease, and antibody levels may persist for long periods after recovery 5