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Test Code CARNP Carbapenemase Detection-Carba NP Test, Varies

Infectious

Useful For

Confirming carbapenemase production from pure isolates of Enterobacterales or Pseudomonas aeruginosa

Additional Tests

Test ID Reporting Name Available Separately Always Performed
CARNB Carbapenemase-Carba NP Test No Yes

Reporting Name

Carbapenemase-Carba NP Test

Specimen Type

Varies


Shipping Instructions


1. For shipping information see Infectious Specimen Shipping Guidelines.

2. Place specimen in a large infectious container (T146) and label as an etiologic agent/infectious substance.



Necessary Information


Specimen source and organism identification are required.



Specimen Required


Specimen Type: Organism

Supplies: Infectious Container, Large (T146)

Container/Tube: Slant

Specimen Volume: Isolate

Collection Instructions: Submit Enterobacterales or Pseudomonas aeruginosa isolate in pure culture (ie, not mixed with other organisms), actively growing.


Specimen Stability Information

Specimen Type Temperature Time Special Container
Varies Ambient (preferred)
  Refrigerated 

Reject Due To

Agar plate Reject

Clinical Information

Gram-negative bacilli (GNB) with acquired carbapenemases have disseminated worldwide, rendering them a global threat. The therapeutic armamentarium for infections caused by carbapenem-resistant Enterobacterales (CRE) is limited, and CRE infections have been associated with significant mortality. Enterobacterales harboring Klebsiella pneumoniae carbapenemase are endemic in some regions of the United States, and although still sporadic, GNB harboring New Delhi metallo-beta-lactamase have been reported from several states. Timely detection of these carbapenemases (along with emerging carbapenemases such as OXA-48 and VIM) is important. Detection is challenging since isolates may have only borderline reductions in susceptibility to carbapenems, and carbapenem resistance may be mediated by mechanisms other than carbapenemases (eg, AmpC or extended-spectrum beta-lactamase with decreased membrane permeability). While molecular methods are confirmatory, testing may not be immediately available and may be limited by the number of targets assayed. The Carba NP test is preferred over the mCIM (modified carbapenem inactivation method) test due to faster turnaround time.

 

If an isolate is suspected to possess KPC or NDM carbapenemase (eg, due to local epidemiology), Carbapenem Resistance Genes, Molecular Detection, PCR, Varies (CARBI) may be preferred over the Carba NP test.

Reference Values

Negative

Interpretation

A positive result indicates production of a carbapenemase by the isolate submitted for testing. A negative result indicates lack of production of a carbapenemase by the isolate submitted for testing.

Cautions

Results of the Carba NP test should be interpreted along with antimicrobial susceptibility testing results. Phenotypic resistance to carbapenems may be due to traits other than carbapenemase production (eg, AmpC or extended-spectrum beta-lactamase production with decreased membrane permeability). Additionally, a positive test is only indicative of carbapenemase production in general; the assay does not determine the type of carbapenemase present (e.g., NDM-1, KPC, OXA-48-like). If an isolate is suspected to possess KPC or NDM carbapenemase (eg, due to local epidemiology), CARBI / Carbapenem Resistance Genes, Molecular Detection, PCR, Varies may be preferred.

 

False-negative results may occur due to plasmid loss in isolates submitted for testing, the presence of a nonexpressed carbapenemase gene, or low-level carbapenemase expression.

Supportive Data

We evaluated 271 gram -negative bacilli (of which 131 were carbapenemase producers and of which 201 were Enterobacterales) using the Carba NP test and the modified Hodge test. Sensitivity for detection of carbapenemase production was comparable (Carba NP, 100 versus modified Hodge test, 98%, p=0.08), but the Carba NP test was more specific (100 versus 80%, p<0.0001) and faster.(1)

Clinical Reference

1. Vasoo S, Cunningham SA, Kohner PC, et al. Comparison of a novel, rapid chromogenic biochemical assay, the Carba NP test, with the modified Hodge test for detection of carbapenemase-producing Gram-negative bacilli. J Clin Microbiol. 2013;51(9):3097-3101

2. Nordmann P, Poirel L, Dortet L. Rapid detection of carbapenemase-producing Enterobacteriaceae. Emerg Infect Dis. 2012;18(9):1503-1507

3. Clinical and Laboratory Standards Institute (CLSI): Performance Standards for Antimicrobial Susceptibility Testing. 33rd ed. CLSI Supplement M100, CLSI; 2023

Method Description

A pure bacterial isolate is emulsified into cell lysis buffer in 2 tubes: one contains the base indicator solution (phenol red with zinc salts) alone and the other contains the base indicator solution plus imipenem (6 mg/mL). The tubes are incubated at 37° C for 2 hours. A positive reaction is indicated by a color change from red to yellow as a result of hydrolysis of the beta-lactam ring of imipenem.(Vasoo S, Cunningham SA, Kohner PC, et al: Comparison of a novel, rapid chromogenic biochemical assay, the Carba NP test, with the modified Hodge test for detection of carbapenemase-producing Gram-negative bacilli. J Clin Microbiol. 2013;51[9]:3097-3101)

Day(s) Performed

Monday through Friday

Report Available

2 to 4 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test 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.

LOINC Code Information

Test ID Test Order Name Order LOINC Value
CARNP Carbapenemase-Carba NP Test 74676-8

 

Result ID Test Result Name Result LOINC Value
CARNP Carbapenemase-Carba NP Test 74676-8

Method Name

Colorimetric Detection of Carbapenem Hydrolysis

Forms

If not ordering electronically, complete, print, and send a Microbiology Test Request (T244) with the specimen.

Specimen Minimum Volume

See Specimen Required