← Product Code [NGZ](/submissions/MI/subpart-b%E2%80%94diagnostic-devices/NGZ) · K040560
# ETEST FOR ANTIFUNGAL SUSCEPTTIBILITY TESTING (K040560)
_Ab Biodisk · NGZ · Jul 27, 2004 · Microbiology · SESE_
**Canonical URL:** https://fda.innolitics.com/submissions/MI/subpart-b%E2%80%94diagnostic-devices/NGZ/K040560
## Device Facts
- **Applicant:** Ab Biodisk
- **Product Code:** [NGZ](/submissions/MI/subpart-b%E2%80%94diagnostic-devices/NGZ.md)
- **Decision Date:** Jul 27, 2004
- **Decision:** SESE
- **Submission Type:** Traditional
- **Regulation:** 21 CFR 866.1640
- **Device Class:** Class 2
- **Review Panel:** Microbiology
## Indications for Use
Etest® is an agar-based gradient technique for quantitative antifungal susceptibility testing of Candida species. It uses a predefined concentration gradient of the specific antifungal agent to determine the Minimum Inhibitory Concentration (MIC) in ug/mL inhibiting the growth of the test organism under defined conditions. This 510k submission is for an application for in wire diagnostic use of Etest for MIC determination of fluconazole, itraconazole and flucytosine with Candida species.
## Device Story
Etest® is an agar-based diagnostic tool for determining antifungal susceptibility of Candida species. The device consists of a 5mm x 60mm inert plastic strip containing a predefined, exponential gradient of a dried antifungal agent. In a clinical laboratory setting, a technician inoculates an agar plate with isolated Candida colonies and applies the strip. The antifungal agent diffuses into the agar, creating a concentration gradient. Following 24-48 hours of incubation at 35°C, a symmetrical inhibition ellipse forms around the strip. The intersection of the inhibition zone edge with the strip indicates the Minimum Inhibitory Concentration (MIC) in ug/mL. Results are read manually by laboratory personnel. The MIC value informs clinicians regarding the susceptibility of the fungal isolate to specific antifungal agents, aiding in the selection of appropriate therapeutic interventions.
## Clinical Evidence
Performance evaluated via multi-site clinical laboratory studies comparing Etest® to the NCCLS M27-A2 broth microdilution reference method. Testing included 591-722 samples per agent. Primary endpoints were Essential Agreement (EA) within ±2 dilutions and Category Agreement (CA). Results: Fluconazole (97.1% EA, 87.6% CA at 48h), Itraconazole (94.7% EA, 84.2% CA at 48h), Flucytosine (98.3% EA, 96.2% CA at 48h). 24-hour readings were found to be less reliable, particularly for Itraconazole (high very major error rate), necessitating 48-hour confirmation.
## Technological Characteristics
Inert, non-porous plastic strip (5mm x 60mm) with a predefined, exponential gradient of dried antifungal agent. Operates via diffusion of the agent into inoculated agar. Manual reading of inhibition ellipse. Requires incubation at 35°C. Medium: RPMI 1640 with 2% glucose and 1.5% Bacto agar per NCCLS M27-A2.
## Regulatory Identification
An antimicrobial susceptibility test powder is a device that consists of an antimicrobial drug powder packaged in vials in specified amounts and intended for use in clinical laboratories for determining in vitro susceptibility of bacterial pathogens to these therapeutic agents. Test results are used to determine the antimicrobial agent of choice in the treatment of bacterial diseases.
## Submission Summary (Full Text)
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510(k) SUBSTANTIAL EQUIVALENCE DETERMINATION
DECISION SUMMARY
DEVICE ONLY TEMPLATE
A. 510(k) Number:
k040560
B. Purpose for Submission:
AST testing of Candida spp.
C. Analyte:
Fluconazole at 0.016-256 ug/mL
Itraconazole at 0.002-32 ug/mL
Flucytosine at 0.002-32 ug/mL
D. Type of Test:
Quantitative AST growth based detection
E. Applicant:
AB BIODISK
F. Proprietary and Established Names:
Etest® for Antifungal Susceptibility Testing
G. Regulatory Information:
1. Regulation section:
866.1640 Antimicrobial Susceptibility Test
2. Classification:
II
3. Product Code:
NGZ Susceptibility testing -antifungal
4. Panel:
83 Microbiology
H. Intended Use:
1. Intended use(s):
Etest® is an agar-based gradient technique for quantitative antifungal susceptibility testing of Candida species. It uses a predefined concentration gradient of the specific antifungal agent to determine the Minimum Inhibitory Concentration (MIC) in ug/mL inhibiting the growth of the test organism under defined conditions.
2. Indication(s) for use:
This indication is for the addition of Etest® for MIC determination of Fluconazole (0.016-256 ug/mL), Itraconazole MIC (0.002-32 ug/mL) and Flucytosine MIC (0.002-32 ug/mL) with Candida species.
3. Special condition for use statement(s):
For prescription use
Preliminary results available at 24 hours with final results available at 48 hours.
4. Special instrument Requirements:
Manual readings only.
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I. Device Description:
Etest® consists of a thin, inert and non-porous plastic strip, 5mm wide and 60 mm long. One side of the strip carries a two-letter code designating the identity of the antifungal agent and is calibrated with MIC values in terms of ug/mL, a predefined and exponential gradient of the dried and established antifungal agent which covers a continuous concentration range across two fold dilutions.
J. Substantial Equivalence Information:
1. Predicate device name(s):
YEASTONE®
2. Predicate K number(s):
K991810
3. Comparison with predicate:
| Similarities | | |
| --- | --- | --- |
| Item | Device | Predicate |
| Intended Use | Quantitative susceptibility to antifungal agents for Candida species | same |
| Incubation | 35° | 35° |
| Inoculation | Isolated colonies of Candida species | same |
| | | |
| Differences | | |
| Item | Device | Predicate |
| Technology | Predefined and preformed antifungal gradient on a plastic strip-growth based | Broth mico-dilution with colorimetric growth indicator- growth based |
| Format | Single gradient strip per antifungal agent | Micro tray with all three antifungal agents |
| Medium | RPMI 1640 as described in NCCLS M27A with 2% glucose and 1.5% Bacto agar | Sensititre® yeast susceptibility inoculum broth |
K. Standard/Guidance Document Referenced (if applicable):
"Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA", Reference Method for Broth Dilution Antifungal Susceptibility Testing of Yeasts: Approved Standard (M27-A2)
L. Test Principle:
The Etest® gradient technology is based on a combination of the concepts of dilution and diffusion test methods for susceptibility testing. Etest® directly quantifies antifungal susceptibility in terms of discrete MIC values. When the Etest® strip containing the antibiotic is applied to an inoculated agar plate, the antifungal agent is immediately released from the plastic surface into the agar. A predefined, continuous gradient of antifungal concentrations is created and maintained directly underneath the strip. After incubation whereby growth becomes visible, a symmetrical inhibition
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ellipse centered along the strip will be seen. The inhibition zone edge intersects the strip of the MIC value in ug/mL of the agent.
## M. Performance Characteristics (if/when applicable):
### 1. Analytical performance:
#### a. Precision/Reproducibility:
Reproducibility was determined by testing 25-26 Candidid spp. one time at each of three sites. The mode was determined and then the reproducibility was calculated based on plus or minus one well of the mode.
| Antifungal agent | Reproducibility at 24 hour Etest readings | Reproducibility at 48 hour Etest readings |
| --- | --- | --- |
| Fluconazole | 73/78 = 93.6% | 78/78 = 100% |
| Itraconazole | 74/75 = 98.7% | 73/75 = 97.3% |
| Flucytosine | 75/75 = 100% | 75/75 = 100% |
#### b. Linearity/assay reportable range:
Not applicable
#### c. Traceability (controls, calibrators, or method):
Quality control was performed each day of testing on both the reference method and the test method. For those results that are different from the NCCLS broth microdilution recommended ranges, additional test data was provided to support the new ranges. Fluconazole
| ORGANISM | Concentration | Reference | Etest® | | |
| --- | --- | --- | --- | --- | --- |
| | | 48h | 24h | 48h* | |
| C. parapsilosis ATCC 22019
Recommended Range at 48h
NCCLS 1-4 ug/mL
Etest 1-4 ug/mL | 0.5 | | | | * |
| | 1 | | 15 | | 7 |
| | 2 | 51 | 32 | 35 | 501 |
| | 4 | 9 | 14 | 26 | 413 |
| | 8 | | | 2 | 109 |
| | | | | | |
| C. krusei ATCC 6258
NCCLS range 16-128 (48h)
Etest range none | 8 | | | | |
| | 16 | | | | |
| | 32 | 32 | 19 | | |
| | 64 | 36 | 32 | | |
| | 128 | | 5 | 1 | |
| | 256 | | 3 | 66 | |
| | | | | | * |
| C. albicans ATCC 90028
Recommended Range at 48h
NCCLS none
Etest 0.125-0.5 ug/mL | 0.064 | | | | |
| | 0.125 | 1 | | 12 | 109 |
| | 0.25 | 38 | 37 | 47 | 668 |
| | 0.5 | 10 | 15 | 3 | 154 |
| | 1 | | 7 | | |
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* For ranges that are different than the NCCLS broth microdilution recommendations additional studies were performed at multiple sites using different lots of Etest® and medium batches.
C. krusei is considered intrinsically resistant to fluconazole and does not make a good control isolate for this drug.
Itraconazole
| ORGANISM | Concen-tration | Reference | Etest® | | |
| --- | --- | --- | --- | --- | --- |
| | | 48h | 24h | 48h* | |
| C. parapsilosis ATCC 22019 Recommended Range at 48h NCCLS .12-.5 ug/mL Etest .064-.25 ug/mL | 0.032 | | 7 | | * |
| | 0.064 | 5 | 22 | 14 | 222 |
| | 0.125 | 29 | 21 | 26 | 533 |
| | 0.25 | 16 | | 10 | 298 |
| | 0.5 | | | | |
| | | | | | |
| C. krusei ATCC 6258 Recommended Range at 48h NCCLS 0.25-1 Etest range 0.25-1 | 0.125 | 2 | 26 | 4 | |
| | 0.25 | 32 | 14 | 21 | |
| | 0.5 | 15 | 7 | 21 | |
| | 1 | 1 | 3 | 4 | |
| | 2 | | | | |
| | | | | | * |
| C. albicans ATCC 90028 Recommended Range at 48h NCCLS none Etest 0.064-0.25ug/mL | 0.032 | 23 | 23 | 8 | |
| | 0.064 | 20 | 25 | 27 | 307 |
| | 0.125 | 5 | | 15 | 443 |
| | 0.25 | | | | 84 |
| | | | | | |
* For ranges that are different than the NCCLS broth microdilution recommendations additional studies were performed at multiple sites using different lots of Etest® and medium batches.
Itraconazole ranges for 24 hour readings are slightly more susceptible and the clinical performance suggests that a 48 hour reading correlates better with the NCCLS reference method.
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Flucytosine
| ORGANISM | Concentration | Reference | Etest® | | |
| --- | --- | --- | --- | --- | --- |
| | | 48h | 24h | 48h* | |
| C. parapsilosis ATCC 22019
Recommended range at 48h
NCCLS 0.12-0.5ug/mL
Etest 0.064-0.25ug/mL | 0.064 | | 18 | 12 | 45* |
| | 0.125 | 23 | 29 | 31 | 321 |
| | 0.25 | 27 | 5 | 9 | 167 |
| | 0.5 | | | | |
| | 1 | | | | |
| | | | | | |
| C. krusei ATCC 6258
NCCLS range
8-32 (48h)
Etest range none | 4 | | | | |
| | 8 | 3 | | | |
| | 16 | 24 | | | |
| | 32 | 25 | 52 | 52 | |
| | | | | | |
| C. albicans ATCC 90028
Recommended Range at 48h
NCCLS none
Etest 0.5-2 ug/mL | 0.125 | | 1 | | * |
| | 0.25 | 3 | 15 | 7 | 5 |
| | 0.5 | 13 | 19 | 21 | 66 |
| | 1 | 36 | 17 | 24 | 399 |
| | 2 | | | | 67 |
* For ranges that are different than the NCCLS broth microdilution recommendations additional studies were performed at multiple sites using different lots of Etest® and medium batches.
A 0.5 McFarland is used to determine the correct inoculum. Colony counts were performed periodically at each site to demonstrate that the inoculum procedure results in the expected CFU/ml.
The no growth rate was <5% for all antifungal agents tested.
d. Detection limit:
Not applicable
e. Analytical specificity:
Not applicable
f. Assay cut-off:
Not applicable
2. Comparison studies:
a. Method comparison with predicate device:
Clinical laboratory studies were performed at three or more clinical laboratories and compared to the NCCLS broth microdilution method as described in M27 A2. Seventy five challenge strains were tested at one site and were included in the evaluation. Both tests were incubated in ambient air at 35°. The reference method was read at 48 hours and the Etest® was read at 24 hours for a preliminary result with a final reading at 48 hours. A two concentration allowance was used for this comparison due to the difficulty in reading the Essential Agreement (EA) for both the reference method
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and the Etest®. Category Agreement (CA) was determined based on the interpretation of each test.
| | total | % EA +/- 2 well | CA | %CA | #R | min | maj | vmj |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Fluconazole | | | | | | | | |
| Candida spp. 24 h* | 591 | 96.6 | 546 | 92.6 | 25 | 45 | 1 | 0 |
| Candida spp. 48h | 596 | 97.1 | 522 | 87.6 | 25 | 69 | 5 | 0 |
| • Etest at 48h is slightly more resistant than the NCCLS reference method
• C. glabrata is responsible for the majority of minor and major errors | | | | | | | | |
| Itraconazole | | | | | | | | |
| Candida spp. 24h* | 713 | 88.8% | 585 | 82% | 111 | 119 | 1 | 8 |
| Candida spp. 48h | 722 | 94.7 | 608 | 84.2 | 112 | 114 | 0 | 1 |
| • The lower than expected category agreement (CA) for itraconazole at both 24 and 48 hour readings are due mainly to minor errors in all species.
• Due to the large number of very major errors itraconazole should not be read at 24 hour | | | | | | | | |
| Flucytosine | | | | | | | | |
| Candida spp. 24h* | 566 | 93.6% | 546 | 96.5 | 30 | 20 | 0 | 0 |
| Candida spp. 48h | 572 | 98.3 | 550 | 96.2 | 30 | 22 | 0 | 0 |
| • Etest is slightly more susceptible than the NCCLS reference method | | | | | | | | |
EA-Essential Agreement
CA-Category Agreement
R-resistant isolates
maj-major discrepancies
vmj-very major discrepancies
min- minor discrepancies
* Readings include only those that were readable at 24h. Majority of the times the 24 hour readings are more susceptible than the 48 hour. In most cases it results in a minor error except for itraconazole which would result in a high very major rate at 24 hour. Confirming these readings at 48 hours removed the errors.
b. Matrix comparison:
Not applicable
3. Clinical studies:
a. Clinical sensitivity:
Not applicable
b. Clinical specificity:
Not applicable
c. Other clinical supportive data (when a and b are not applicable):
Not applicable
4. Clinical cut-off:
Not applicable
5. Expected values/Reference range:
| Fluconazole | ≤ 8, 16-32, ≥ 64 ug/mL |
| --- | --- |
| Itraconazole | ≤ 0.125, 0.25-0.5, ≥ 1 ug/mL |
| Flucytosine | ≤ 4, 8-16, ≥ 32 ug/mL |
N. Conclusion:
The submitted information in this premarket notification is complete and supports a substantial equivalence decision.
---
**Source:** [https://fda.innolitics.com/submissions/MI/subpart-b%E2%80%94diagnostic-devices/NGZ/K040560](https://fda.innolitics.com/submissions/MI/subpart-b%E2%80%94diagnostic-devices/NGZ/K040560)
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