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HelpTest ID: ACARP Acanthamoeba species Molecular Detection, PCR, Ocular
Useful For
Aids in the diagnosis of amebic keratitis in conjunction with clinical findings
Method Name
Real-Time Polymerase Chain Reaction (PCR)/ DNA Probe Hybridization
Reporting Name
Acanthamoeba species Detection, PCRSpecimen Type
VariesOrdering Guidance
Although verification experiments did not detect Acanthamoeba species DNA in contact lenses from asymptomatic adults, it is possible that the polymerase chain reaction may detect asymptomatic colonization/contamination and, therefore, testing should not be performed on asymptomatic individuals.
Necessary Information
1. Specimen source is required.
2. Source information should include main anatomical site of collection.
3. If submitting scrapings or swabs, specify which collection device was used (ie, scalpel or swab).
Specimen Required
The preferred specimen for this test is corneal scraping or biopsy.
Submit only 1 of the following specimens:
Specimen Type: Tissue (fresh)
Sources: Ocular
Container/Tube: Sterile container
Specimen Volume: 5-10 mm
Collection Instructions: Submit tissue in a sterile container with 1 mL of sterile saline, minimal essential media (MEM), or viral transport media.
Preferred Paraffin-Embedded Tissue Block:
Supplies: Tissue Block Container (T553)
Specimen Type: Formalin-fixed, paraffin-embedded tissue block (FFPE)
Sources: Ocular
Container/Tube: Tissue block
Collection Instructions: Submit a FFPE tissue block to be cut and returned.
Acceptable Paraffin-Embedded Tissue Block:
Specimen Type: FFPE section
Sources: Ocular
Container/Tube: Sterile container for each individual cut section (scroll).
Collection Instructions: Perform microtomy and prepare five separate 10-micron sections. Each section (scroll) must be placed in a separate sterile container for submission.
Specimen Type: Scrapings
Sources: Eye, ocular, cornea
Container/Tube: Sterile container
Specimen Volume: 1 mL
Collection Instructions:
1. Collect corneal scrapings using a scalpel or other sharp device to remove the outer layer of cells from the eye.
2. Swish the collection device in 1 mL of sterile saline, MEM, or viral transport media.
3. Remove the scalpel blade or sharp device from the collection container before submitting to the lab.
4. Specimens containing scalpel blades will be canceled.
Specimen Type: Swabs
Sources: Eye, ocular, cornea
Container/Tube: Sterile container
Specimen Volume: 1 mL
Collection Instructions:
1. Swab must be placed into viral transport media and submitted with the specimen.
2. Specimens received without swabs will be canceled.
Additional Information: Swabs are not the preferred specimen for this test and may yield false-negative results.
Specimen Type: Contact lenses
Container/Tube: Sterile container
Specimen Volume: Entire collection
Collection Instructions:
1. Place entire contact lens in a sterile container with 1 mL sterile saline, viral transport media, or MEM.
2. Right and left lenses must be submitted individually using multiple sterile containers or in the original contact lens case. A separate order must be created for each lens being tested.
3. Indicate Right or Left in the specimen source.
Specimen Type: Contact lens cases without lenses
Container/Tube: Sterile container
Specimen Volume: 1 mL solution or entire case
Additional Information:
1. Depending on the type of case submitted, it may be necessary to test right and left chambers individually. A separate order must be created for each chamber being tested.
2. Indicate Right or Left in the specimen source.
Specimen Minimum Volume
Scrapings: 0.5 mL; Other specimen types: See Specimen Required
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Refrigerated (preferred) | 7 days | |
| Frozen | 7 days |
Clinical Information
Acanthamoeba are ubiquitous, free-living, microscopic amebae that cause rare, but severe, infections of the eye, skin, lungs, and central nervous system (CNS). They are found worldwide in water and soil and may enter the body through inhalation, contamination of wounds, and contact lens use. As many as 24 species comprising 22 genotypes (T1-T22) have been described using 18S ribosomal RNA sequence analysis, although most human infections are due to genotype T4. Given their widespread distribution in the environment, many people will be exposed to Acanthamoeba during their lifetime, but very few will become sick from this exposure.
The most common form of Acanthamoeba infection is amebic keratitis (AK). Infection occurs primarily in contact lens wearers due to contamination of lenses, cleaning solutions, or storage cases. Amebae can also enter the cornea following trauma. AK is a painful, subacute corneal infection associated with extensive scarring and blindness if untreated. Cases generally respond to treatment, but relapse is common. Compared to corneal infection, involvement of the CNS is rare and seen primarily in severely immunocompromised individuals, such as organ transplant recipients and patients with AIDS. CNS infection may also be caused by a related ameba, Balamuthia mandrillaris.
AK is usually clinically suspected based on symptoms and confocal ophthalmologic examination. Confirmation of infection is classically identified by microscopic examination and culture of corneal tissue and contact lenses or equipment using tap water agar plate overlain with bacteria as a food source for the amebae. Unfortunately, it must be held and examined for 7 days for maximum sensitivity. A polymerase chain reaction assay provides a more rapid result with similar sensitivity to culture and is, therefore, the preferred method for confirming the clinical diagnosis of AK.
Reference Values
Negative
Interpretation
A positive result indicates the presence of Acanthamoeba species DNA and is consistent with active or recent infection. While positive results are highly specific indicators of disease, they should be correlated with symptoms, clinical findings, radiologic features, or confocal ophthalmologic examination.
Clinical Reference
1. Cope JR, Ali KM, Visvesvara GS: Pathogenic and opportunistic free-living amebae. In: Carroll KC, Pfaller MA, Landry ML, et al, eds. Manual of Clinical Microbiology. 12th Ed. ASM Press; 2019:chap142
2. Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Division of Foodborne, Waterborne, and Environmental Diseases (DFWED): Parasites - Acanthamoeba - Granulomatous Amebic Encephalitis (GAE); Keratitis. CDC; Updated December 29, 2021. Accessed March 28, 2023. Available at www.cdc.gov/parasites/acanthamoeba/health_professionals/acanthamoeba_keratitis_hcp.html
Day(s) Performed
Monday through Sunday
Report Available
2 to 3 daysTest Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
87798
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| ACARP | Acanthamoeba species Detection, PCR | 41429-2 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| SRCAS | Specimen Source | 31208-2 |
| 38058 | Acanthamoeba species PCR | 41429-2 |
Forms
If not ordering electronically, complete, print, and send a Microbiology Test Request (T244) with the specimen.