Test Catalog

Test Id : MRSAP

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Methicillin Resistant Staphylococcus aureus, PCR, Nasal

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Overview

Test Catalog

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

Rapid screening test for Staphylococcus aureus nasal carriage that, if positive, indicates whether the S aureus is methicillin susceptible or resistant

 

This test should not be used to guide or monitor treatment for methicillin-resistant S aureus or S aureus infections.

Highlights

This test provides rapid presurgical screening of patients for colonization of Staphylococcus aureus and methicillin-resistant S aureus in the nasal cavity

Method Name
A short description of the method used to perform the test

Real-Time Polymerase Chain Reaction (PCR)

NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.

Yes

Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test

Staph aureus/MRSA, Nasal, PCR

Aliases
Lists additional common names for a test, as an aid in searching

Pre-surgical screening

S aureus

S. aureus

SSI

Staphylococcus aureus

Surgical Site Infection

MRSA

Specimen Type
Describes the specimen type validated for testing

Swab

Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing

Specimen Type: Nasal cavity swab

Supplies: BD E-Swab (T853)

Container/Tube:

Preferred: BD Liquid Amies Elution Swab (E-Swab)

Acceptable: Copan Liquid Amies Elution Swab (ESwab); Cepheid nasal sample collection device (dual swab in liquid Stuart media); or Copan swab and transport systems (LQ Stuart or LQ Amies) (scored swabs only)

Specimen Volume: Entire collection

Collection Instructions:

1. Ask the patient to blow their nose prior to collection.

2. Use one swab for both right and left nares.

3. Insert the white Dacron swab tip (do not insert any further in) into the anterior nares.

4. Rotate the swab for 3 seconds against the nasal mucosa. Apply slight pressure on the outside of the nose with your finger to ensure good contact.

5. Repeat the process on the other nostril.

6. Insert the swab back into the carrier. The swabs should go all the way into the transport container. Tightly cap the container.

7. Label the transport container with patient label and send refrigerate.

Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the Testing Laboratory

See Specimen Required. 

Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected

Incorrect swab collection/non-scored swabs Reject

Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included

Specimen Type Temperature Time Special Container
Swab Refrigerated (preferred) 5 days
Ambient 24 hours

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

Rapid screening test for Staphylococcus aureus nasal carriage that, if positive, indicates whether the S aureus is methicillin susceptible or resistant

 

This test should not be used to guide or monitor treatment for methicillin-resistant S aureus or S aureus infections.

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

Staphylococcus aureus causes a variety of human infections and is a major cause of hospital acquired infection of surgical wounds and infections associated with indwelling medical devices. Mayo Clinic has established a program to reduce the number of S aureus surgical infections, which involves surgical patients being tested for S aureus and treated, if positive, prior to surgery. This assay not only detects S aureus, but, if positive, indicates whether S aureus is methicillin susceptible or resistant.

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 Staphylococcus aureus

Negative for methicillin-resistant S aureus

Interpretation
Provides information to assist in interpretation of the test results

A positive result indicates presence of DNA from Staphylococcus aureus. The assay also detects the gene for methicillin resistance (mecA).

 

A negative result indicates the absence of detectable S aureus DNA in the specimen.

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

Results from the Xpert SA Nasal Complete Assay should be interpreted in conjunction with other laboratory and clinical data available to the clinician and should be used as an adjunct to nosocomial infection control efforts to identify patients needing enhanced precautions. Results should not be used to guide or monitor treatment for methicillin-resistant Staphylococcus aureus (MRSA) or S aureus infections.

 

Erroneous test results might occur from improper specimen collection, failure to follow the recommended specimen collection, handling and storage procedures, technical error, sample mix-up, or because the number of organisms in the specimen is too low to be detected by the test.

 

A positive test result does not necessarily indicate the presence of viable organisms. It is, however, presumptive for the presence of S aureus or MRSA.

 

An Xpert SA Nasal Complete Assay positive result does not necessarily indicate intervention eradication failure since nonviable DNA may persist. A negative result following a previously positive test result may or may not indicate eradication success.

 

A negative result does not negate the presence of MRSA or S aureus.

 

Concomitant cultures are necessary to recover organisms for epidemiological typing or for further susceptibility testing.

 

The performance characteristics were not established by Cepheid for patients 21 years of age or younger.

 

Mutations or polymorphisms in primer or probe binding regions may affect detection of new or unknown S aureus or MRSA variants resulting in a false-negative result. 

 

In samples containing both MRSA and methicillin-susceptible S aureus, the Xpert SA Nasal Complete Assay may not detect the MRSA organisms. The pivotal clinical study included one sample with documented mixed infection; the Xpert SA Nasal Complete Assay identified the sample as MRSA positive/S aureus positive.

 

In a mixed culture, the analytical limit of MRSA detection is variable when extremely high concentrations of S aureus are present. Competition from S aureus was observed at a MRSA: S aureus ratio of 1:1x10(6) in 7 of 8 SCCmec types tested. For SCCmec type VIII, competition from SA was observed at a MRSA: S aureus ratio of 1:1x10(3).

 

Inhibition of the SA Nasal Complete Assay resulting in invalid test results has been observed in the presence of inhaled nasal steroids Flonase and Nasonex in SA negative samples at concentrations greater than 5% (volume to volume [v/v}), and 10% (v/v), respectively.

 

Inhibition of the SA Nasal Complete Assay resulting in false-negative test results has been observed in the presence of inhaled nasal steroids Flonase and Nasonex in MRSA positive samples at concentrations greater than 1% (v/v) and 5% (v/v), respectively.

 

The Xpert SA Nasal Complete Assay may generate a false-positive MRSA result when testing a mixed infection nasal specimen containing both methicillin-resistant coagulase-negative Staphylococcus species and empty cassette S aureus.

 

The Xpert SA Nasal Complete Assay may generate false-negative MRSA results when testing borderline oxacillin-resistant S aureus (BORSA). The mechanism of oxacillin resistance in BORSA strains is due to an increased production of beta-lactamases, not mecA. BORSA with oxacillin minimum inhibitory concentrations (MIC) of 4 to 8 mcg/mL are considered borderline resistant but would be reported as MRSA negative by the Xpert SA Nasal Complete Assay. BORSA strains are rare in the United States.

 

The Xpert SA Nasal Complete Assay may generate false-negative MRSA results when testing modified S aureus (MOD-SA). The mechanism of oxacillin resistance in MOD-SA strains is due to changes in affinity of penicillin binding proteins for oxacillin, not mecA. MOD-SA with oxacillin MIC of 4 to 8 mcg/mL are considered borderline resistant but would be reported as MRSA negative by the Xpert SA Nasal Complete Assay. MOD-SA strains are rare in the United States.

 

There may be an association with false-positive results in specimens containing blood.

 

Xpert SA Nasal Complete assay results may sometimes be invalid due to a failed SPC control, error, or no result and require retesting, which can lead to a delay in obtaining final results.

 

As with all in vitro diagnostic tests, positive and negative predictive values are highly dependent on prevalence. Xpert SA Nasal Complete assay performance may vary depending on the prevalence and population tested.(1)

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

1. Xpert SA Nasal Complete 300-8799. Package insert: Cepheid; Rev H, 09/2019

2. Muto C, Jernigan J, Ostrowsky BE, et al: SHEA guideline for preventing nosocomial transmission of multidrug-resistant strains of Staphylococcus aureus and Enterococcus. Infect Control Hosp Epidemiol. 2003 May;24(5):362-386

3. Carr AL, Daley MJ, Givens Merkel K, Rose DT. Clinical utility of methicillin-resistant Staphylococcus aureus nasal screening for antimicrobial stewardship: A review of current literature. Pharmacotherapy. 2018 Dec;38(12):1216-1228. doi: 10.1002/phar.2188

4. Saraswat MK, Magruder JT, Crawford TC, et al: Preoperative Staphylococcus aureus screening and targeted decolonization in cardiac surgery. Ann Thorac Surg. 2017 Oct;104(4):1349-1356. doi: 10.1016/j.athoracsur.2017.03.018

5. Chen AF, Wessel CB, Rao N. Staphylococcus aureus screening and decolonization in orthopaedic surgery and reduction of surgical site infections. Clin Orthop Relat Res. 2013;471(7):2383-2399. doi: 10.1007/s11999-013-2875-0

Method Description
Describes how the test is performed and provides a method-specific reference

The GeneXpert Dx System automates and integrates sample purification, nucleic acid amplification, and detection of the target sequence in simple or complex samples using real-time polymerase chain reaction (PCR). The system uses single-use disposable cartridges that hold the PCR reagents and host the PCR process. Because the cartridges are self-contained, cross-contamination between samples is minimized.

 

The Cepheid Xpert SA Nasal Complete Assay performed in the GeneXpert System is a qualitative in vitro diagnostic test designed for rapid detection of Staphylococcus aureus and methicillin-resistant S aureus (MRSA) from nasal swabs in patients at risk for nasal colonization. The test utilizes automated PCR for qualitative detection of proprietary sequences for the staphylococcal protein A (spa) gene, the gene for methicillin resistance (mecA), and the staphylococcal MRSA/SA S aureus DNA cassette chromosome mec (SCCmec) inserted into the S aureus chromosomal attB site. The assay includes a sample processing control to ensure the sample was processed correctly and to monitor for the presence of inhibitors in the PCR reaction. A probe check control verifies reagent rehydration, PCR tube filling in the cartridge, probe integrity, and dye stability.(Package insert: Xpert SA Nasal Complete 300-8799. Cepheid; Rev H, 09/2019)

PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information

No

Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.

Monday through Sunday

Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.

1 day

Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

5 days

Performing Laboratory Location
Indicates the location of the laboratory that performs the test

Rochester

Fees
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.

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  • Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
  • Prospective clients should contact their account representative. For assistance, contact Customer Service.

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 instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

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 Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.

CPT codes are provided by the performing laboratory.

87641

LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.

Test Id Test Order Name Order LOINC Value
MRSAP Staph aureus/MRSA, Nasal, PCR 72887-3
Result Id Test Result Name Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
MRSAC MRSA, PCR 72887-3
MSSAC Staphylococcus aureus, PCR 79447-9

Test Setup Resources

Setup Files
Test setup information contains test file definition details to support order and result interfacing between Mayo Clinic Laboratories and your Laboratory Information System.

Excel | PHP Pdf | CMS Pdf

Sample Reports
Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports
International System (SI) of Unit reports are provided for a limited number of tests. These reports are intended for international account use and are only available through MayoLINK accounts that have been defined to receive them.

SI Normal Reports | SI Abnormal Reports