Etanercept (Enbrel®)

The drug Etanercept (trade name Enbrel®) is a dimeric fusion protein consisting of the extracellular ligand-binding portion of the human 75 kilodalton (p75) tumor necrosis factor receptor (TNFR) linked to the Fc portion of human IgG1. Etanercept binds specifically to human tumor necrosis factor alpha (TNF-α) and blocks its interaction with cell surface TNF receptors. It was possible to show that the surveillance of circulating Etanercept concentration during maintenence therapy represents a direct and/or indirect factor for immunogenicity and some other side effects. In this context, identification of biomarkers for (non-)response and risk factors for adverse drug reactions that might be related to serum concentrations and maintaining the effective concentration of Etanercept in order to potentially avoid some side effects with a reliable method might be beneficial. Enzyme immunoassay (ELISA) test kit for the determination of free Etanercept (Enbrel®) in serum and plasma. The catcher is TNF-α and the detection antibody is a HRP-labeled mAb binding at the Fc part of the drug. Due to the assay design there is full cross reactivity with other TNF-α catchers. This kit is for research use only, not for use in diagnostic procedures.
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Protocol PDF Click for Protocol
Catalog Number TK01307
Species Human
Design Enzyme immunoassay (ELISA) technique.
Standards 5 standards, ready to use.
Controls None provided.
Sample Types Serum and plasma.
Sample Volume 10 µL
Assay Desc. 60 min. incubation (RT) + 30 min. (RT) + 15 min. (RT) = 1 hour, 45 min. total incubation time.
Standard Range 0 / 6 - 200 ng/mL
Sensitivity 5 ng/mL
Other Names
Storage 2 - 8°C
Postscript For research use only, not for use in diagnostic procedures.

Intended use

This ELISA kit applies to the in vitro quantitative determination of Etanercept (Enbrel®) concentrations in serum, plasma and other biological fluids.

Test principle

This ELISA kit uses the Sandwich-ELISA principle. The micro ELISA plate provided in this kit has been pre-coated with an antigen specific to Etanercept (Enbrel®). Standards or samples are added to the micro ELISA plate wells and combined with the specific antigen. Then a biotinylated detection antigen specific for Etanercept (Enbrel®) and Avidin-Horseradish Peroxidase (HRP) conjugate are added successively to each micro plate well and incubated. Free components are washed away. The substrate solution is added to each well. Only those wells that contain Etanercept (Enbrel®), biotinylated detection antigen and Avidin-HRP conjugate will appear blue in color. The enzyme-substrate reaction is terminated by the addition of stop solution and the color turns yellow. The optical density (OD) is measured spectrophotometrically at a wavelength of 450 nm ± 2 nm. The OD value is proportional to the concentration of Etanercept (Enbrel®). You can calculate the concentration of Etanercept (Enbrel®) in the samples by comparing the OD of the samples to the standard curve.

Typical data

As the OD values of the standard curve may vary according to the conditions of the actual assay performance (e.g. operator, pipetting technique, washing technique or temperature effects), the operator should establish a standard curve for each test. Typical standard curve and data is provided below for reference only.


Intra-assay Precision (Precision within an assay):
3 samples with low, middle,high concentration of Etanercept (Enbrel®). And the sample of Etanercept (Enbrel®) were tested 30 times on one plate, respectively.
Inter-assay Precision (Precision between assays):
3 samples with low, middle,high concentration of Etanercept (Enbrel®). And the sample of Etanercept (Enbrel®) were tested on 3 different plates, 30 replicates in each plate.


Matrices listed below were spiked with certain level of Etanercept (Enbrel®) and the recovery rates were calculated by comparing the measured value to the expected amount of Etanercept (Enbrel®) in samples.

Matrix Recovery range (%) Average Recovery (%)
Serum (n=5) 89-100 97
EDTA plasma (n=5) 89-99 96
heparin plasma (n=5) 81-96 94


The linearity of the kit was assayed by testing samples spiked with appropriate concentration of Etanercept (Enbrel®) and their serial dilutions. The results were demonstrated by the percentage of calculated concentration to the expected.

    Serum (n=5) EDTA plasma (n=5) heparin plasma (n=5)
1:2 Range (%) 88-108 90-108 91-103
Average (%) 94 93 93
1:4 Range (%) 87-101 91-101 87-104
Average (%) 93 93 95
1:8 Range (%) 87-106 89-106 87-103
Average (%) 94 94 95
1:16 Range (%) 89-105 94-105 94-107
Average (%) 93 95 94


The stability of Etanercept (Enbrel®) is determined by the loss rate of activity. The loss rate of Etanercept (Enbrel®) is less than 5% within the expiration date under appropriate storage condition. To minimize extra influence on the performance, operation procedures and lab conditions, especially room temperature, air humidity, incubator temperature should be strictly controlled. It is also strongly suggested that the whole assay is performed by the same operator from the beginning to the end.

Item Specifications Storage
Micro ELISA Plate(Dismountable) 8 wells ×12 strips -20℃, 6 months
Reference Standard 2 vials
Concentrated Biotinylated Detection Ab (100×) 1 vial, 120 μL
Concentrated HRP Conjugate (100×) 1 vial, 120 μL -20℃(shading light), 6 months
Reference Standard & Sample Diluent 1 vial, 20 mL 4℃, 6 months
Biotinylated Detection Ab Diluent 1 vial, 14 mL
HRP Conjugate Diluent 1 vial, 14 mL
Concentrated Wash Buffer (25×) 1 vial, 30 mL
Substrate Reagent 1 vial, 10 mL 4℃(shading light)
Stop Solution 1 vial, 10 mL 4℃
Plate Sealer 5 pieces
Product Description 1 copy
Certificate of Analysis 1 copy

Other supplies required

Microplate reader with 450 nm wavelength filter
High-precision transfer pipette, EP tubes and disposable pipette tips
Incubator capable of maintaining 37℃
Deionized or distilled water
Absorbent paper
Loading slot for Wash Buffer

Assay procedure summary

1. Prepare all reagents, samples and standards;
2. Add 100µL standard or sample to each well. Incubate 1 hours at 37°C;
3. Aspirate and add 100µL prepared Detection Reagent A. Incubate 1 hour at 37°C;
4. Aspirate and wash 3 times;
5. Add 100µL prepared Detection Reagent B. Incubate 30 minutes at 37°C;
6. Aspirate and wash 5 times;
7. Add 90µL Substrate Solution. Incubate 10-20 minutes at 37°C;
8. Add 50µL Stop Solution. Read at 450nm immediately.

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