Chagas disease laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Yazan Daaboul, M.D.

Overview

Acute Chagas disease is often diagnosed by peripheral blood smear following the visual detection of T. cruzi parasite. Serology is often helpful for chronic cases only, where assay positivity of both "whole parasite lysate" and "recombinant antigen" is usually required for the diagnosis. Although PCR is sensitive in acute cases (e.g. exposure following organ transplantation), its sensitivity and specificity are variable in the chronic state and highly depend on the pre-test probability.

Laboratory Findings

Blood smear

• Acute Chagas disease is often diagnosed by visual detection of the T. cruzi parasite on peripheral blood smear.
• Peripheral blood smears are usually stained with Giemsa stain for adequate visualization of the parasite.

Serology

• Serology is not usually helpful in acute Chagas disease.
• Detection of anti-trypanosomal IgG antibodies is helpful to detect chronic Chagas disease infections.

• A single assay for chronic T. cruzi infection is neither sensitive nor specific, and positive results from both "whole parasite lysate" and "recombinant antigens" are required to make the diagnosis of chronic Chagas disease.
• Detection of antibodies among infants may be difficult due to the presence of maternal antibodies early following birth. Accordingly, serologic testing for infants is only recommended at least 9 months after birth.

PCR

• In acute disease, PCR is very sensitive and is widely used today to detect accidental exposure among organ transplant recipients following organ transplantation
• In chronic disease, PCR sensitivity and specificity depend on the pre-test probability of Chagas disease.

• Serial PCR measurements are often necessary to confirm the diagnosis of Chagas disease.

• Quantitative PCR is helpful to monitor for Chagas reactivation, and increasing parasitic load on PCR is considered a sensitive surrogate of reactivation.

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  Trypanosoma cruzi in blood smear. From Public Health Image Library (PHIL).

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  Giemsa-stained micrograph shows a Trypanosoma cruzi protozoan parasite during its leishmanial stage of development. From Public Health Image Library (PHIL).

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  Micrograph of Trypanosoma cruzi in a blood smear using Giemsa staining technique. From Public Health Image Library (PHIL).

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  Micrograph revealing Trypanosoma cruzi parasites in a blood smear using Giemsa staining technique (100x mag). From Public Health Image Library (PHIL).