Test Id : GUSAB
Guselkumab Antibodies, Serum
Useful For
Suggests clinical disorders or settings where the test may be helpful
Evaluation of patients with loss of response to guselkumab, with recurrence of symptoms, or low or undetectable serum guselkumab measured at trough
Method Name
A short description of the method used to perform the test
Only orderable as part of profile. For more information see GUSAP / Guselkumab Quantitation with Antibodies, Serum.
Electrochemiluminescent-Bridging Immunoassay (ECLIA)
NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test
Aliases
Lists additional common names for a test, as an aid in searching
Janssen Biotech
Anti-IL23 blocker
Antibodies-to-Guselkumab
Crohn's disease
Plaque psoriasis
Psoriatic arthritis
GUS
Guselkumab
Guselkumab antibodies
Tremfya
Tremfya antibodies
Specimen Type
Describes the specimen type validated for testing
Serum
Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing
Only orderable as part of profile. For more information see GUSAP / Guselkumab Quantitation with Antibodies, Serum.
Patient Preparation: For 12 hours before specimen collection, patient should not take multivitamins or dietary supplements (eg, hair, skin, and nail supplements) containing biotin (vitamin B7).
Supplies: Sarstedt Aliquot Tube 5 mL (T914)
Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 0.6 mL serum
Collection Instructions:
1. Draw blood immediately before next scheduled dose (trough specimen).
2. Within 2 hours of collection, centrifuge and aliquot serum into a plastic vial.
Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the testing laboratory. The minimum volume is sufficient for one attempt at testing.
Serum: 0.5 mL
Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected
| Gross hemolysis | OK |
| Gross lipemia | Reject |
| Gross icterus | OK |
| Heat-treated specimens | 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 |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 28 days | |
| Ambient | 14 days | ||
| Frozen | 28 days |
Useful For
Suggests clinical disorders or settings where the test may be helpful
Evaluation of patients with loss of response to guselkumab, with recurrence of symptoms, or low or undetectable serum guselkumab measured at trough
Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Guselkumab (Tremfya; Johnson and Johnson) is a fully human IgG1 lambda therapeutic monoclonal antibody used for the treatment of moderate to severe ulcerative colitis (UC) and Crohn disease (CD), as well as plaque psoriasis and psoriatic arthritis. Guselkumab targets interleukin (IL) 23A (IL-23p19) binding with high affinity to the p19 subunit and inhibiting further action.
Therapeutic drug monitoring (TDM) has become standard of care in the gastroenterology practice for biologic therapies used in CD and UC. TDM is routinely used to assess loss of response to therapy and proactively manage patients taking tumor necrosis factor inhibitors (eg, infliximab and adalimumab), alpha-4-beta7 integrins (vedolizumab), and IL-12/23 blockers (ustekinumab). With the approval of guselkumab for inflammatory bowel disease, TDM is expected to play an important role in managing loss of response to therapy and guide decision making for use of monotherapy or combination therapy.
Guselkumab, like other therapeutic monoclonal antibodies, is immunogenic. Clinical trials have shown that antibodies-to-guselkumab occur at rates of about 6% to 9% for plaque psoriasis, 2% for psoriatic arthritis, 11% for UC, and 5% for CD. The presence of anti-drug antibodies against therapeutic monoclonal antibodies has been shown to impact clinical efficacy, either by accelerated clearance or by inhibition of target binding. Assessment for the presence of antibodies to guselkumab (ATG) may be important for the management of patients, especially for those individuals with sub-therapeutic trough concentrations of guselkumab. For those individuals demonstrating loss of response in the context of sub-therapeutic drug concentrations, the presence of ATG may indicate the need to transition to another treatment approach. In contrast, those individuals with sub-therapeutic drug concentrations in the absence of detectable ATG may benefit from dose escalation.
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.
Only orderable as part of profile. For more information see GUSAP / Guselkumab Quantitation with Antibodies, Serum.
Antibodies to guselkumab
<9.8 ng/mL
Interpretation
Provides information to assist in interpretation of the test results
The presence of detectable anti-guselkumab antibodies may be associated with increased guselkumab clearance and lower circulating concentrations of guselkumab in serum. Low trough concentrations of guselkumab may be correlated with loss of response to the drug.
Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Clinical management decisions for patients receiving guselkumab treatment should not be based solely on quantitation of guselkumab or assessment of antibodies to guselkumab (ATG). Test results must be interpreted within the clinical context of the patient.
Therapeutic ranges have not been established for guselkumab quantitation. Therapeutic concentrations of guselkumab may vary according to the disease (eg, Crohn disease vs psoriatic arthritis vs psoriasis).
Interference with the ATG assay, in the form of depressed signal, was observed in samples containing more than 200 ng/mL biotin.
Clinical Reference
Recommendations for in-depth reading of a clinical nature
1. Janssen Biotech, Inc. Highlights of prescribing information: Tremfya (guselkumab) 2017. Updated September 2025. Accessed October 2, 2025. Available at www.janssenlabels.com/package-insert/product-monograph/prescribing-information/TREMFYA-pi.pdf
2. The efficacy and safety of guselkumab induction therapy in patients with moderately to severely active ulcerative colitis: Results from the Phase 3 QUASAR Induction Study. Gastroenterol Hepatol (N Y). 2023;19(7 Suppl 3):9-10
3. Peyrin-Biroulet L, Allegretti JR, Rubin DT, et al. Guselkumab in patients with moderately to severely active ulcerative colitis: QUASAR Phase 2b Induction Study. Gastroenterology. 2023;165(6):1443-1457. doi:10.1053/j.gastro.2023.08.038
4. Danese S, Panaccione R, Feagan BG, et al. Efficacy and safety of 48 weeks of guselkumab for patients with Crohn’s disease: maintenance results from the phase 2, randomized, double-blind GALAXI-1 trial. Lancet Gastroenterol Hepatol. 2024;9(2):133-146
5. Shao J, Vetter M, Vermeulen A, et al. Combination therapy with guselkumab and golimumab in patients with moderately to severely active ulcerative colitis: Pharmacokinetics, immunogenicity and drug-drug interactions. Clin Pharmacol Ther. 2024;115(6):1418-1427
6. Ladwig PM, Barnidge DR, Willrich MAV. Mass spectrometry approaches for identification and quantitation of therapeutic monoclonal antibodies in the clinical laboratory. Clin Vaccine Immunol. 2017;24(5):e00545-16
7. Sharma K, da Silva BC, Hanauer SB. The role of immunogenicity in optimizing biological therapies for inflammatory bowel disease. Expert Rev Gastroenterol Hepatol. 2025;19(3):243-258
Method Description
Describes how the test is performed and provides a method-specific reference
Testing for antibodies to guselkumab is accomplished using a laboratory-developed immunoassay.(Unpublished Mayo method)
PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information
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.
Thursday
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.
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
Indicates the location of the laboratory that performs the test
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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- 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 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.
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.
CPT codes are provided by the performing laboratory.
83520
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 |
|---|---|---|
| GUSAB | Guselkumab Ab, S | No LOINC Needed |
| 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.
|
|---|---|---|
| 623122 | Guselkumab Ab, S | In Process |
| 623291 | GUSAB Interpretation | 77202-0 |