Test ID: PTOX
Toxoplasma gondii, Molecular Detection, PCR
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Diagnosing central nervous system toxoplasmosis
Method Name A short description of the method used to perform the test
Polymerase Chain Reaction (PCR)/DNA Probe Hybridization
(PCR is utilized pursuant to a license agreement with Roche Molecular Systems, Inc.)
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Forms: If not ordering electronically, submit a Microbiology Request Form (Supply T244) with the specimen.
Specimen source is required.
Submit only 1 of the following specimens:
Preferred:
Specimen Type: Amniotic fluid
Container/Tube: Amniotic fluid container
Specimen Volume: 0.5 mL
Collection Instructions: Do not centrifuge.
Specimen Stability Information: Refrigerated (preferred)/Frozen
Specimen Type: Spinal fluid
Container/Tube: Sterile vial
Specimen Volume: 0.5 mL
Collection Instructions: Do not centrifuge.
Specimen Stability Information: Refrigerated (preferred)/Frozen
Specimen Type: Fresh tissue
Container/Tube: Sterile container with 1 to 2 mL of sterile saline or multi-microbe medium (M5) (Supply T484)
Specimen Volume: Entire collection
Collection Instructions: Submit only fresh tissue
Specimen Stability Information: Refrigerated
Specimen Type: Ocular fluid
Container/Tube: Body fluid container
Specimen Volume: 0.3 mL
Collection Instructions: Do not centrifuge.
Specimen Stability Information: Refrigerated (preferred)/Frozen
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | NA |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Varies | Varies | 7 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Toxoplasma gondii is an intracellular protozoan parasite that chronically infects about 10% of the adult population in the United States. Transmission may occur by ingestion of undercooked meat containing cysts, by direct contact with the feces of an infected cat excreting infectious oocysts, and vertically through the placenta. Accurate diagnosis is crucial because of the different therapeutic options.
Central nervous system (CNS) toxoplasmosis most often occurs as a complication of HIV infection. Diagnosis of CNS toxoplasmosis is difficult by serologic methods, and direct detection of the organism in cerebrospinal fluid (CSF) by stain and culture is not sensitive. PCR detection of Toxoplasma gondii DNA in CSF is a rapid, sensitive, and specific method for the diagnosis of CNS toxoplasmosis.
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 for the presence of Toxoplasma gondii DNA
Interpretation Provides information to assist in interpretation of the test results
A positive result indicates presence of DNA from Toxoplasma gondii.
Negative results indicate absence of detectable DNA but does not exclude the presence of organism or active or recent disease.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This assay is designed to detect only species of clinical significance and is to be used for patients with a clinical history and symptoms consistent with toxoplasmosis. This test should not be used to screen healthy patients. Depending on the population, varying percentages of patients may be found to be positive.
Results should be interpreted with consideration of clinical and laboratory findings. A negative result does not indicate absence of disease. Reliable results depend on adequate specimen collection and the absence of inhibiting substances.
Supportive Data
Accuracy/Diagnostic Sensitivity and Specificity:
The LightCycler real-time PCR method was compared to PCR-enzyme-linked immunosorbent assay (ELISA) for detecting the B1 gene of Toxoplasma gondii on 95 cerebrospinal fluid (CSF) clinical specimens received in the laboratory. Using the PCR-ELISA method as the gold standard, the diagnostic sensitivity and specificity of the assay was 82% (9 of 11 positives detected).
Supplemental Data (Spiking Studies):
To supplement the above data, 30 negative patient specimens (30 each: CSF, amniotic fluid, ocular fluid, and fresh tissue) were spiked with toxoplasma-positive control plasmid at the limit of detection (50 copies per microliter). The specimens were run in a blinded manner along with 30 of each specimen type negative (nonspiked) specimens; 97% to 100% of the spiked specimens were positive and 100% of the nonspiked specimens were negative.
Analytical Sensitivity/Limit of Detection (LoD):
The limit of detection for this assay was 50 copies/microliter in CSF, tissue, and body fluid (specifically ocular and amniotic fluid).
Analytical Specificity:
No PCR signal was obtained from extracts of 20 bacterial, parasitic, and viral isolates from similar organisms and from organisms (panel of 14 CSF with known viral and bacterial infections) commonly found in the specimen types tested.
Precision:
Intra-assay precision was 100% and inter-assay precision was 100%.
Reference Range:
A review of the literature indicates the reference range is "Negative" for this assay.
Reportable Range:
This is a qualitative assay and results are reported as "Negative" or "Positive for Toxoplasma gondii DNA."
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Luft BJ, Remington JS: Toxoplasmic encephalitis in AIDS. Clin Infect Dis 1992 Aug;15(2):211-222
2. Sterkers Y, Varlet-Marie E, Marty P, et al: Diversity and evolution of methods and practices for the molecular diagnosis of congenital toxoplasmosis in France: a four years survey. Clin Microbiol Infect 2009 Nov 2
3. Villard O, Filisetti D, Roch-Deries F, et al: Comparison of enzyme-linked immunosorbent assay, immunoblotting, and PCR for diagnosis of toxoplasmic chorioretinitis. J Clin Microbiol 2003 Aug;41(8):3537-3541
4. Jones JL, Kruszon-Moran D, Sanders-Lewis K, Wilson M: Toxoplasma gondii infection in the United States, 1999-2004, decline from the prior decade. Am J Trop Med Hyg 2007 Sep;77(3):405-10
Method Description Describes how the test is performed and provides a method-specific reference
This assay uses the commercially produced LightCycler system. To perform the procedure, DNA is extracted from cerebrospinal fluid (CSF).Toxoplasma gondii is detected by using PCR to amplify the target sequence of the B1 gene. The LightCycler amplifies and monitors fluorescent development of target nucleic acid after each cycle. The continuous monitoring is derived from the fluorescence resonance energy transfer (FRET) principle: a hybridization probe with a donor fluorophore on the 3' end is excited by an external light source and emits light that is absorbed by a second hybridization probe with an acceptor fluorophore at the 5' end. The acceptor fluorophore emits light of a different wavelength that can be measured with a signal that is proportional to the amount of specific PCR product.(Cockerill FR, Uhl FR: Applications and challenges of real-time PCR for the clinical microbiology laboratory. In Rapid Cycle Real-Time PCR. Edited by U Reischl, C Wittwer, F Cockerill. Springer, NY, 2002)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Saturday; Varies
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
87798
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| SRC74 | Specimen Source | 31208-2 |
| 81795 | Toxoplasma gondii PCR | 42626-2 |
External
link
PDF
document
Excel
document
Word
document