Instructions for use

FT4 ELISA 2nd Generation

TF E-2200R

fT4 ELISA 2nd Generation
INTENDED USE
For the direct quantitative determination of Free Thyroxine by an enzyme immunoassay in human serum.
For in vitro diagnostic use only.
PRINCIPLE OF THE TESTThe principle of the following enzyme immunoassay test follows the typical competitive binding scenario.
Competition occurs between an unlabelled antigen (present in standards, controls and patient samples) and anenzyme-labelled antigen (conjugate) for a limited number of antibody binding sites on the microplate. Thewashing and decanting procedures remove unbound materials. After the washing step, the enzyme substrate isadded. The enzymatic reaction is terminated by addition of the stopping solution. The absorbance is measured
on a microtiter plate reader. The intensity of the colour formed is inversely proportional to the concentration of
fT4 in the sample. A set of standards is used to plot a standard curve from which the amount of fT4 in patient
samples and controls can be directly read.
The labelled T4 (conjugate) employed in this assay system has shown no binding properties towards thyroxinebinding globulin (TBG) and human serum albumin (HSA). The binding sites on the microplates are designed tobe of a low binding-capacity in order not to disturb the equilibrium between T4 and its carrying proteins. The
assay is carried out under normal physiological conditions of pH, temperature and ionic strength.
CLINICAL APPLICATIONS
Thyroxine (T4), the principal thyroid hormone, circulates in blood almost completely bound to carrier proteins.
However, only the free (unbound) fraction of thyroxine is considered to be biologically active. The main carriersof thyroxine are thyroxine-binding globulin (TBG), pre-albumin and albumin. The measurement of freethyroxine (fT4) levels correlate better with the clinical status than total thyroxine levels.
The free T4 assay is a one step competitive ELISA system that is rapid and easy to perform compared toequilibrium dialysis and ultrafiltration methods, which are cumbersome and time-consuming. This system
employs a highly specific monoclonal antibody and a non-analog tracer that was proved experimentally to haveno signify cant binding to TBG and albumin.
In the euthyroid, normal population the free T4 concentration is 7–22 pg/ml. The level of free T4 is decreased
in hypothyroidism while in thyrotoxic patients the level of free T4 is increased.
This assay is used at times with other thyroid tests for in vitro diagnostic purposes and for assessing patients
who are receiving thyroid treatments (follow-up).
PROCEDURAL CAUTIONS AND WARNINGS
1. Users should have a thorough understanding of this protocol for the successful use of this kit. Reliable
performance the instructions provided.
2. Control materials or serum pools should be included in every run at a high and low level for assessing thereliability of results.
3. When the use of water is specified for dilution or reconstitution, use deionized or distilled water.
4. In order to reduce exposure to potentially harmful substances, gloves should be worn when handling kit
reagents and human specimens.
5. All kit reagents and specimens should be brought to room temperature and mixed gently but thoroughly
before use. Avoid repeated freezing and thawing of reagents and specimens.
6. A standard curve must be established for every run.
7. The controls should be included in every run and fall within established confidence limits.
8. Improper procedural techniques, imprecise pipetting, incomplete washing as well as improper reagent
storage may be indicated when assay values for the controls do not reflect established ranges.
9. When reading the microplate, the presence of bubbles in the wells will affect the optical densities (ODs).
Carefully remove any bubbles before performing the reading step.
10. The substrate solution (TMB) is sensitive to light and should remain colourless if properly stored. Instability
or contamination may be indicated by the development of a blue colour, in which case it should not beused.
11. When dispensing the substrate and stopping solution, do not use pipettes in which these liquids will comeinto contact with any metal parts.
12. To prevent contamination of reagents, use a new disposable pipette tip for dispensing each reagent,
sample, standard and control.
13. Do not mix various lot numbers of kit components within a test and do not use any component beyond theexpiration date printed on the label.
14. Kit reagents must be regarded as hazardous waste and disposed of according to national regulations.

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LIMITATIONS
1. All the reagents within the kit are calibrated for the direct determination of fT4 in human serum. The kit isnot calibrated for the determination of fT4 in other specimens of human or animal origin.
2. Do not use grossly hemolyzed, grossly lipemic, icteric or improperly stored serum.
3. Any samples or control sera containing azide or thimerosal are not compatible with this kit, as they maylead to false results.
4. Samples reading higher than 100 pg/ml should be reported as such and should not be diluted. Dilution willalter the existing equilibrium and may lead to false results.
5. The interpretation of free T4 results can be complicated by a variety of drugs, severe nonthyroidal illness
and some rare conditions such as familial dysalbuminemic hyperthyroxinemia (FDH). For diagnostic
purposes, the results of this assay should always be used in combination with the clinical examination,
medical history and other findings.
6. Some individuals may have antibodies to mouse protein that can possibly interfere in this assay. Therefore,
the results from any patients who have received preparation of mouse antibodies for diagnosis or therapy
should be interpreted with caution.
SAFETY CAUTIONS AND WARNINGS
POTENTIAL BIOHAZARDOUS MATERIAL
Human serum that may be used in the preparation of the standards and controls has been tested and found to
be nonreactive for Hepatitis B surface antigen and has also been tested for the presence of antibodies to HCV
and Human Immunodeficiency Virus (HIV) and found to be negative. No test method however, can offer
complete assurance that HIV, HCV and Hepatitis B virus or any infectious agents are absent. The reagentsshould be considered a potential biohazard and handled with the same precautions as applied to any blood
specimen.
CHEMICAL HAZARDS
Avoid contact with reagents containing TMB, hydrogen peroxide and sulfuric acid. If contacted with any of thesereagents, wash with plenty of water. TMB is a suspected carcinogen.
SPECIMEN COLLECTION AND STORAGE
Approximately 0.1 ml of serum is required per duplicate determination. Collect 4–5 ml of blood into an
appropriately labelled tube and allow it to clot. Centrifuge and carefully remove the serum layer. Store at 4 °C
for up to 24 hours or at -10 °C or lower if the analyses are to be done at a later date. Consider all humanspecimens as possible biohazardous materials and take appropriate precautions when handling.
SPECIMEN PRETREATMENT
This assay is a direct system; no specimen pretreatment is necessary.
REAGENTS AND EQUIPMENT NEEDED BUT NOT PROVIDED
1. Precision pipettes to dispense 25, 100, 150 and 300 μl
2. Disposable pipette tips3. Distilled or deionized water
4. A 37 oC incubator
5. Microplate reader with a filter set at 450 nm and an upper OD limit of 3.0 or greater*(see assay procedure step 11).
REAGENTS PROVIDED
1. AA E-0030

Wash Buffer Concentrate – Requires Preparation X10

Contents:

One bottle containing buffer with a non-ionic detergent and a non-mercury preservative.

Volume:50 ml/bottle

Storage:

Refrigerate at 2 - 8 oC

Stability:

12 months or as indicated on label.

Preparation:

Dilute 1:10 in distilled or deionized water before use. If the whole plate is to be used dilute
50 ml of the wash buffer concentrate in 450 ml of water.
TMB Substrate - Ready To Use.

2. AA E-0055
Contents:

One bottle containing tetramethylbenzidine and hydrogen peroxide in a non-DMF or DMSO
containing buffer.

Volume:16 ml/bottle

Storage:

Refrigerate at 2 - 8 oC

Stability:

12 months or as indicated on label.

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Stopping Solution - Ready To Use.

3. AA E-0080
Contents:

One vial containing 1M sulfuric acid.

Volume:6 ml/bottle

Storage:

Refrigerate at 2 - 8 oC

Stability:

12 months or as indicated on label.

Hazards
identification:
H290 May be corrosive to metals.
H314 Causes severe skin burns and eye damage.
4. Standards and Controls- Ready To Use.
Listed below are approximate concentrations, please refer to vial labels for exact concentrations:Cat. no.

SymbolStandard

TF E-2201

Standard A

Concentration
0 pg/ml

Volume/Vial
0.5 mlTF E-2202

Standard B

2 pg/ml

0.5 mlTF E-2203

Standard C

6 pg/ml

0.5 mlTF E-2204

Standard D

20 pg/ml

0.5 mlTF E-2205

80 pg/ml

0.5 mlTF E-2251

Standard EControl 1

0.5 mlTF E-2252

Control 2

Refer to vial labels for expectedvalue and acceptable range!

0.5 mlContents:

fT4 in a human serum-based matrix with a non-mercury preservative. Prepared by spiking
serum with a defined quantity of T4.

Storage:

Refrigerate at 2 - 8 oC

Stability:

12 months in unopened vials or as indicated on label. Once opened, the standards should be
used within 14 days or aliquoted and stored frozen. Avoid multiple freezing and thawing
cycles.

5. TF E-2213
Contents:

Assay Buffer - Ready To Use.
One vial containing a protein-based buffer with a non-mercury preservative.

Volume:15 ml/bottle

Storage:

Refrigerate at 2 - 8 oC

Stability:

12 months or as indicated on label.
Mouse Anti-fT4 Antibody-Coated Break-Apart Well Microplate - Ready
To Use.

6. TF E-2231
Contents:

One 96 well (12x8) monoclonal antibody-coated microplate in a resealable pouch withdesiccant.

Storage:

Refrigerate at 2 - 8 oC

Stability:

12 months or as indicated on label.

7. TF E-2240

fT4-Horseradish Peroxidase (HRP) Conjugate Concentrate – Requires
Preparation X50

Contents:

fT4-HRP conjugate in a protein-based buffer with a non-mercury preservative.

Volume:300 µl/vial

Storage:

Refrigerate at 2 - 8 oC

Stability:

12 months or as indicated on label.

Preparation:

Dilute 1:50 in assay buffer before use (eg. 40 μl of HRP in 2 ml of assay buffer). If the wholeplate is to be used dilute 240 μl of HRP in 12 ml of assay buffer. Discard any that is left over.

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ASSAY PROCEDURE
Specimen Pretreatment: None.
All reagents must reach room temperature before use. Standards, controls and specimen samples should beassayed in duplicate. Once the procedure has been started, all steps should be completed without interruption.
1.

Prepare working solutions of the fT4-HRP conjugate and wash buffer.

2.

Remove the required number of well strips. Reseal the bag and return any unused strips to therefrigerator.

3.

Pipette 25 μl of each standard, control and specimen sample into correspondingly labelled wells induplicate.

4.

Pipette 100 μl of the conjugate working solution into each well.
(We recommend using a multichannel pipette.)

5.

Gently shake the plate for 10 seconds.

6.

Incubate the plate at 37oC for 1 hour.

7.

Wash the wells 3 times with 300 µl of diluted wash buffer per well and tap the plate firmly against
absorbent paper to ensure that it is dry.
(The use of a washer is recommended).

8.

Pipette 150 μl of TMB substrate into each well at timed intervals.

9.

Incubate the plate on at 37oC for 10 - 15 minutes(or until Standard A attains dark blue colour for desired OD).

10.

Pipette 50 μl of stopping solution into each well at the same timed intervals as in step 8.

11.

Read the plate on a microplate reader at 450 nm within 20 minutes after addition of the stopping solution.
If the OD exceeds the upper limit of detection or if a 450 nm filter is unavailable, a 405 or 415nm filter may
be substituted. The optical densities will be lower, however, this will not affect the results of patient/control
samples.

CALCULATIONS
1. Calculate the mean optical density of each standard duplicate.
2. Draw a standard curve on semi-log paper with the mean optical densities on the Y-axis and the standardconcentrations on the X-axis. If immunoassay software is being used, a 4-parameter or 5-parameter curveis recommended.
3. Calculate the mean optical density of each unknown duplicate.
4. Read the values of the unknowns directly off the standard curve.
TYPICAL TABULATED DATA
Sample data only. Do not use to calculate results.
Standard

OD 1

OD 2

Mean OD

AB
C
DE
Unknown

2.043
1.886
1.709
1.032
0.266
1.332

2.094
1.973
1.727
1.049
0.283
1.312

2.068
1.929
1.718
1.041
0.274
1.322Value(pg/ml)
0262080
13.0

TYPICAL STANDARD CURVE

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PERFORMANCE CHARACTERISTICSSENSITIVITY
The lower detection limit is calculated from the standard curve by determining the resulting concentration ofthe mean OD of Standard A (based on 10 replicate analyses) minus 2 SD. Therefore, the sensitivity of theDirect fT4 ELISA kit is 1.0 pg/ml.
SPECIFICITY (CROSS REACTIVITY)
The following compounds were tested for cross-reactivity with the Direct fT4 ELISA kit with T4 cross-reacting at100%.
Compound
L-ThyroxineD-Thyroxine
3,3’,5’-Triiodo-L-Thyronine(Reverse T3)
3,3’,5-Triiodo-L-Thyronine (T3)3,3’,5’-Triiodo-D-Thyronine
3,3’,5’-Triiodothyropropionic acid% Cross Reactivity
1009486
3.3
1.8
0.6

The following compounds were tested but cross-reacted at less than 0.04%: Acetylsalicylic acid, 3,5-Diiodo-LThyronine, 3,5-Diiodo-L-Tyrosine and 3-Iodo-L-Tyrosine.
INTRA-ASSAY PRECISION
Three samples were assayed ten times each on the same standard curve. The results (in pg/ml) are tabulated
below:Sample
123Mean
3.79
23.26
70.60

SD
0.16
1.14
3.04

CV %
4.8
4.9
4.3

INTER-ASSAY PRECISION
Three samples were assayed ten times over a period of four weeks. The results (in pg/ml) are tabulated below:
Sample
12
3

Mean
4.27
20.54
67.34

SD
0.53
2.36
6.67

CV %
12.3
11.5
9.9

EXPECTED NORMAL VALUESAs for all clinical assays each laboratory should collect data and establish their own range of expected normal
values. The following reference range (pg/ml) was established with 80 apparently healthy adults:GroupNormal Euthyroid
SamplesNRange (pg/ml)

80

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EFFECT OF BILIRUBIN
Bilirubin was added to a patient sample at concentrations of 50 and 100 μg/ml and assayed with the Direct fT4
ELISA kit. Results are tabulated below:
SampleUnspiked+ 50 µg/ml bilirubin+ 100 µg/ml bilirubin

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fT4 (pg/ml)
8.78
10.68
9.72

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EFFECT OF HUMAN SERUM ALBUMIN (HSA)
Purified human serum albumin (HSA) was added to a patient sample at concentrations of 10, 20 and 40 mg/ml.
Samples were assayed with the Direct fT4 ELISA kit. Results are tabulated below:
SampleFT4 (pg/ml)
8.78
Unspiked
8.81+10 mg/ml
9.46+20 mg/ml
9.90+40 mg/ml
No binding of labelled fT4 to HSA was found at these concentrations.
EFFECT OF THYROXINE-BINDING GLOBULIN (TBG)
The Standard A was spiked precisely with purified TBG at concentrations ranging from 25-200 μg/ml andassayed with the Direct fT4 ELISA kit. Results are tabulated below:
TBG AddedOD 450 nm(μg/ml)
101.883
225
2.030
350
2.149
41002.175
52002.251
No significant binding of labelled fT4 to TBG was found at these concentrations.
Sample

EFFECT OF NON-ESTERIFIED FATTY ACIDS
Oleic acid was added to a patient sample at concentrations of 0.5, 5 and 20 mmol/l and assayed with the Direct
fT4 ELISA kit. Results are tabulated below:
SamplefT4 (pg/ml)
24.83
Unspiked
20.53+0.5 mmol/l
26.06+5 mmol/l
83.64+20 mmol/l
At high concentrations of oleic acid, the free T4 level was significantly increased. This is due to the well-known
effect that non-esterified fatty acids can dissociate T4 from its carrier proteins.
REFERENCES
1. Ingbar SH, et al. J Clin Invest. 1965; 44(10):1679–89.
2. Robbins J. Metabolism. 1973; 22(8):1021–6.
3. Schall RF Jr., et al. Clin Chem. 1978; 24(10):1801–4.
4. Selenkow HA, Robin NI. J Maine Med Assoc. 1970; 61:199–211.
5. Oppenheimer JH, et al. J Clin Invest. 1963; 42:1769–82.
6. Young DS, et al. Clin Chem. 1975; 21(5):1D–432D.
7. Sterling K, Hegedus J Clin Invest. 1962; 41: 1031–40.
8. Cavalieri RR, et al. Clin Res. 1967; 15:124.
9. Comoglio S, Celada F. J Immunol Methods. 1976; 10(2–3):161–70.
10. McComb RB, Bowers GN, Posen S. In: Alkaline Phosphatase, 1st Ed. New York: Plenum Press; 1979: 525–704.

Symbols:

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Storagetemperature

Manufacturer

Contains sufficient for<n> tests

Expiry date

Batch code

For in-vitro diagnostic
use only!

Consult instructions
for useContent

CE labelledCaution

Catalogue
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