Test Catalog

Test ID: STRNG    
Strongyloides Antibody, IgG, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Screening for the presence of IgG-class antibodies to Strongyloides

 

Not useful for monitoring patient response to therapy as IgG-class antibodies to Strongyloides may remain detectable following resolution of infection.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Strongyloidiasis is caused by Strongyloides stercoralis, a nematode endemic to tropical and subtropical regions worldwide. S stercoralis is also prominent in the southeastern United States, including in rural areas of Kentucky, Tennessee, Virginia, and North Carolina. A small series of epidemiological studies in the United States identified that between 0 to 6.1% of individuals sampled had antibodies to S stercoralis.

 

S stercoralis has a complex lifecycle that begins with maturation to the infective filariform larva in warm, moist soil. The larvae subsequently penetrate exposed skin and migrate hematogenously to the lungs, from where they ascend the bronchial tree and are swallowed. Once in the small intestine, filariform larva mature into the adult worms that burrow into the mucosa. Gravid female worms produce eggs that develop into noninfectious rhabditiform larvae in the gastrointestinal tract and are eventually released in the stool. The time from dermal penetration to appearance of Strongyloides in stool samples is approximately 3 to 4 weeks.

 

The most common manifestations of infection are mild and may include epigastric pain, mild diarrhea, nausea, and vomiting. At the site of filariform penetration, skin may be inflamed and itchy-this is referred to as "ground itch." Migration of the larva through the lungs and up the trachea can produce a dry cough, wheezing, and mild hemoptysis. Eosinophilia, though common among patients with strongyloidiasis, is not a universal finding and the absence of eosinophilia cannot be used to rule-out infection.

 

In some patients, particularly those with a depressed immune system, the rhabditiform larvae may mature into the infectious filariform larvae in the gastrointestinal tract and lead to autoinfection. The filariform larvae subsequently penetrate the gastrointestinal mucosa, migrate to the lungs and can complete their lifecycle. Low-level autoinfection can maintain the nematode in the host for years to decades. Among patients who become severely immunocompromised, however, autoinfection may lead to hyperinfection and fatal disseminated disease. Hyperinfection has also been associated with underlying human T-cell lymphotropic virus type 1 (HTLV-1) infection. Uncontrolled, the larvae can disseminate to the lungs, heart, liver, and central nervous system. Septicemia and meningitis are common in cases of Strongyloides hyperinfection due to seeding of the bloodstream and central nervous system with bacteria originating from the gastrointestinal tract.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative

Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

Positive:

IgG antibodies to Strongyloides were detected, suggesting current or past infection. False-positive results may occur with other helminth infections (eg, Trichinella, Taenia solium). Clinical correlation is required.

 

Negative:

No detectable levels of IgG antibodies to Strongyloides. Repeat testing in 10 to 14 days if clinically indicated.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

False-positive results may occur with other helminth infections, including prior exposure to Entamoeba histolytica, Ascaris, Taenia solium, Fasciola species, Echinococcus species, Schistosoma species, and Toxocara (per assay manufacturer).

 

This assay should not be used alone to establish a diagnosis of strongyloidiasis. Results should be correlated with other laboratory findings and through clinical evaluation.

 

False-negative results may occur during acute or localized infection. A single negative result should not be used to rule-out infection.

  

The seroprevalence of IgG-class antibodies to Strongyloides stercoralis ranges from 0 to 6.1% in the United States.

Supportive Data

Accuracy:

The Bordier Strongyloides EIA was compared to the Strongyloides Luciferase Immunoprecipitation Assay as performed at the NIH and to the SciMedix Strongyloides IgG ELISA using 102 serum samples. Based on prior publications, the LIPS assay was considered the gold standard comparator for this evaluation.(1,2) The comparative data is shown below in Tables 1, 2, and 3:

 

Table 1. Comparison of Results Between the Bordier and NIH LIPS assays (n=102)

 

NIH LIPS

Positive

Negative

Bordier

Positive

51

12

Negative

3

36

 

 

 

 

 

 

 

 

Positive Agreement: 96.2% (51/53); 95% Confidence Interval (CI): 86.5%-99.7%

Negative Agreement: 75.0% (36/48); 95% CI: 61.1%-85.2%

Overall Agreement: 85.3% (87/102); 95% CI: 77.0%-91.0%

 

Table 2. Comparison of Results Between the Bordier and SciMedx assays (n=102)

 

SciMedx

Positive

Negative

Equivocal

Bordier

Positive

45

13

5

Negative

8

30

1

 

 

 

 

 

 

 

 

Positive Agreement: 84.9% (45/53); 95% CI: 72.7%-92.4%

Negative Agreement: 69.8% (30/43); 95% CI: 54.8%-81.5%

Overall Agreement: 73.5% (75/102); 95% CI: 64.2%-81.2%

 

Table 3. Comparison of Results Between the SciMedx and NIH LIPS assays (n=102)

 

NIH LIPS

Positive

Negative

SciMedix

Positive

42

11

Negative

7

36

Equivocal*

5

1

 

 

 

 

 

 

 

 

 

*Equivocal results were excluded from calculation of positive and negative agreement.

 

Positive Agreement: 85.7% (42/49); 95% CI: 73.0%-93.2%

Negative Agreement: 76.6% (36/47); 95% CI: 62.6%-86.6%

Overall Agreement: 76.5% (78/102); 95% CI: 67.3%-83.7%

 

Reference Range:

Evaluation was performed on 100 normal donor serum samples by the Bordier Strongyloides assay and 99% (99/100) were negative.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Ramanathan R, Burbelo PD, Groot S, et al: A luciferase immunoprecipitation systems assay enhances the sensitivity and specificity of diagnosis of Strongyloides stercoralis infection. J Infect Dis 2008;198(3):444-451

2. Starr MC, Montgomery SP: Soil-transmitted Helminthiasis in the United States: a systematic review-1940-2010. Am J Trop Med Hyg 2011;85(4):680-684

3. Krolewiecki AJ, Ramanathan R, Fink V, et al: Improved diagnosis of Strongyloides stercoralis using recombinant antigen-based serologies in a community-wide study in northern Argentina. Clin Vaccine Immunol 2010;17(10):1624-1630

4. Centers for Disease Control and Prevention. Global Health. Division of Parasitic Diseases and Malaria. Stongyloides. Epidemiology and Risk Factors. Accessed March 2014. Available at www.cdc.gov/parasites/strongyloides/epi.html

Special Instructions Library of PDFs including pertinent information and forms related to the test