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Test Code ACARP Acanthamoeba species Molecular Detection, PCR, Ocular

Secondary ID

64717

Useful For

Aids in the diagnosis of amebic keratitis in conjunction with clinical findings

Method Name

Real-Time Polymerase Chain Reaction (PCR)/TaqMan DNA Probe Hybridization

Reporting Name

Acanthamoeba species Detection, PCR

Specimen Type

Varies


Advisory Information


Specimens collected using wooden shafted swabs will be canceled.

 

Fluorescein dye may interfere with testing and should not be used prior to collection. Specimens containing fluorescein dye will be canceled.

 

Although verification experiments did not detect Acanthamoeba species DNA in contact lenses from asymptomatic adults, it is possible that PCR may detect asymptomatic colonization/contamination and, therefore, testing should not be performed on asymptomatic individuals.



Necessary Information


Specimen source is required.



Specimen Required


The preferred specimen for Acanthamoeba PCR from an ocular source 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. 

    

Specimen Type: Tissue: Formalin-fixed paraffin-embedded (FFPE)

Sources: Ocular

Container/Tube: Sterile container      

Specimen Volume: 5-10 mm

Collection Instructions: Cut tissue into five, 10-micron sections and place in a sterile container. 

 

Specimen Type: Scrapings/Swabs

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, minimal essential media (MEM), or viral transport media.

3. Remove the collection device from the collection container before submitting to the lab.

4. Specimens containing scalpel blades 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, contact lens solution, viral transport media, or minimal essential media (MEM). 

2. Right and Left lenses must be submitted individually using multiple sterile containers or in the original contact lens case. Multiple orders must be created. 

3. Indicate Right or Left in the specimen source.

 

Specimen Type: Contact lens solution

Container/Tube: Sterile container

Specimen Volume: 1 mL solution

 

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. Multiple orders must be created.

2. Indicate Right or Left in the specimen source.


Specimen Minimum Volume

Tissue: 5 mm biopsy
Scrapings: 0.5 mL
Contact Lens Solution: 1 mL

Specimen Stability Information

Specimen Type Temperature Time
Varies Refrigerated 7 days

Reject Due To

Hemolysis

NA

Lipemia

NA

Icterus

NA

Other

Specimens containing scalpel blades, swabs with wooden handles, or fluorescein dye

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 18 genotypes (T1-T18) have been described, 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. PCR 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, and confocal ophthalmologic examination.

Clinical Reference

1. Trabelsi H, Dendana A, Sellami A, et al: Pathogenic free-living amoebae: epidemiology and clinical review. Pathol Biol (paris) 2012;60:399-405

2. Thompson PP, Kowalski RP, Shanks RM, Gordon YJ: Validation of real-time PCR for laboratory diagnosis of Acanthamoeba keratitis. J Clin Microbiol 2008;46:3232-3236

Day(s) and Time(s) Performed

Monday through Saturday

Analytic Time

2 days

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. 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