3.       PRINCIPLES  OF  THE METHOD

The Bio-Line CT.-ELISA is a solid phase Enzyme Amplified Sensitivity Immunoassay performed on microtiterplates.    Calibrators and samples react with the capture monoclonal antibody (MAb 1) coated on microtiter well and with a monoclonal antibody (MAb 2) labelled with horseradish peroxidase (HRP).  After an incubation period allowing the formation of a sandwich: coated MAb 1 – human CT – MAb 2 – HRP, the microtiterplate is washed to remove unbound enzyme labelled antibody.   Bound enzyme-labelled antibody is measured through a chromogenic reaction.  Chromogenic solution (TMB ready for use) is added and incubated.  The reaction is stopped with the addition of Stop Solution and the microtiterplate is then read at the appropriate wavelength.   The amount of substrate turnover is determined colourimetrically by measuring the absorbance, which is proportional to the Calcitonin concentration. 

A calibration curve is plotted and Calcitonin concentration in samples is determined by interpolation from the calibration curve.  The use of the ELISA reader (linearity up to 3 OD units) and a sophisticated data reduction method (polychromatic data reduction) result in a high sensitivity in the low range and in an extended calibration range.

4        REAGENTS PROVIDED

Note: 1.   CT free human serum is to be used for samples dilution.

          2.   1 pg of our reference preparation is equivalent to 0.19 μIU MRC 89/620.

5        SUPPLIES NOT PROVIDED 

The following material is required but not provided in the kit:

1.           High quality distilled water

2.           Pipettes for delivery of: 50 μl, 100 μl, 200 µl, 500 µl and 1 ml (the use of accurate pipettes with disposable plastic tips is recommended)

3.           Vortex mixer

4.           Magnetic stirrer

5.           Horizontal microtiterplate shaker capable of 700 rpm ± 100 rpm

6.           Washer for microtiterplates

7.           Microtiterplate reader capable of reading at 450 nm, 490 nm and 650 nm (in case of polychromatic reading) or capable of reading at 450 nm and 650 nm (monochromatic reading)

8.           Optional equipment: The ELISA-AID™ necessary to read the plate according to polychromatic reading (see paragraph XI.A.) can be purchased from Robert Maciels Associates, Inc. Mass. 0.2174 USA.

6        REAGENT PREPARATION

a.       Calibrators : Reconstitute the calibrators with 0.5 ml distilled water.

b.       Controls : Reconstitute the controls with 0.5 ml distilled water.

c.      Working Wash solution : Prepare an adequate volume of Working Wash solution by adding 199 volumes of distilled water to 1 volume of Wash Solution (200x). Use a magnetic stirrer to homogenize. Discard unused Working Wash solution at the end of the day.

d.       CT Free Serum: Reconstitute the CT Free Serum with the amount of Buffer as indicated on the vial label.  Allow it to remain undisturbed until completely dissolved, then mix well by gentle inversion.

e.        Working anti-CT-HRP conjugate: Following the number of wells to be used, dilute the concentrated conjugate (11x) with the conjugate buffer in a clear glass vial according to the table below.  Extemporaneous dilution is recommended.

  7.        STORAGE  AND  EXPIRATION  DATING  OF  REAGENTS

§             Before opening or reconstitution, all kits components are stable until the expiry date, indicated on the vial label, if kept at 2 to 8°C.

§             Unused strips must be stored, at 2-8°C, in a sealed bag containing a desiccant until expiration date.

§             After reconstitution, calibrators, controls and CT free serum should be frozen immediately after use and kept at –20°C for 3 months.  Only one freeze thawing cycle is allowed, discard the calibrators, controls and CT free serum after the second use.

§             The concentrated Wash Solution is stable at room temperature until expiration date.

§             Freshly prepared Working Wash solution should be used on the same day.

§             After its first use, the concentrated conjugate (11x) is stable until expiry date, if kept in the original well-closed vial at 2 to 8°C.

§             The Working anti-CT-HRP conjugate is stable for 1 week at 4°C.

§             The chromogenic TMB solution and the Stop Solution are stable at 2°C to 8°C until the expiry date.

§             Alterations in physical appearance of kit reagents may indicate instability or deterioration.

8.       SPECIMEN  COLLECTION  AND  PREPARATION

§             Serum and plasma must be kept at 2 - 8°C.

§             If the test is not run within 24 hours, storage in aliquots at -20°C is recommended.  Avoid subsequent freeze thaw cycles.

§             Prior to use, all samples should be at room temperature.  It is recommended to vortex the samples before use.

§             Serum or EDTA plasma provide similar results. 

Y(serum) = 0.84 x (EDTA plasma) – 2.4 pg/ml       r=0.90  n=15

§             Do not use haemolysed samples.

§             Do not use lipemic samples.

9        PROCEDURE

A.       Handling notes

          Do not use the kit or components beyond expiry date. 

Do not mix materials from different kit lots. 

Bring all the reagents to room temperature prior to use.

          Thoroughly mix all reagents and samples by gentle agitation or swirling.

          Perform calibrators, controls and samples in duplicate.  Vertical alignment is recommended.

          Use a clean plastic container to prepare the Wash Solution.

          In order to avoid cross-contamination, use a clean disposable pipette tip for the addition of each reagent and sample.

          For the dispensing of the Chromogenic Solution and the Stop Solution avoid pipettes with metal parts.

          High precision pipettes or automated pipetting equipment will improve the precision. 

          Respect the incubation times. 

          Prepare a calibration curve for each run, do not use data from previous runs.

The chromogenic solution should be colourless.   If a dark blue colour develops within a few minutes after preparation, this indicates that the preparation is unusable and must be discarded.

Dispense the Chromogenic Solution within 15 minutes following the washing of the microtiterplate. 

During incubation with Chromogenic Solution, avoid direct sunlight on the microtiterplate.

B.       Procedure

1.           Select the required number of strips for the run.  The unused strips should be resealed in the bag with a desiccant and stored at 2-8°C.

2.           Secure the strips into the holding frame. 

3.           Pipette 50 µl of each Calibrator, Control and Sample into the appropriate wells.

4.           Pipette 100 µl of Working anti-CT-HRP conjugate into all the wells.

5.           Incubate for 18 ± 1 hour at 2-8°C.

6.           Aspirate the liquid from each well.

7.           Wash the plate 4 times by:

§      dispensing 0.4 ml of Wash Solution into each well

§      aspirating the content of each well

8.           Pipette 50 µl of the Chromogenic solution into each well within 15 minutes following the washing step.

9.           Incubate the microtiterplate for 30 minutes at room temperature on a horizontal shaker set at 700 rpm ± 100 rpm, avoid direct sunlight.

10.        Pipette 200 µl of Stop Solution into each well.

11.        Read the absorbances at 450 nm and 490 nm (reference filter 630 nm or 650 nm) within 3 hours and calculate the results as described in section XI.

10.     CALCULATION  OF  RESULTS

A.       Polychromatic Reading:

1.           In this case, the ELISA-AID™ software will do the data processing.

2.           The plate is first read at 450 nm against a reference filter set at 650 nm (or 630 nm).

3.           A second reading is performed at 490 nm  against the same reference filter.

4.           The ELISA-AID™ Software will drive the reader automatically and will integrate both readings into a polychromatic model.  This technique can generate OD’s up to 10.

5.           The principle of polychromatic data processing is as follows:

§          Xi = OD at 450 nm

§          Yi = OD at 490 nm

§          Using a standard unweighted linear regression, the parameters A & B are calculated : Y = A*X – B

§          If Xi < 3 OD units, then X calculated = Xi

§          If Xi > 3 OD units, then X calculated = (Yi-B)/A

§          A 4-parameter logistic curve fitting is used to build up the calibration curve.

§          The CT concentration in samples is determined by interpolation on the calibration curve.

B.       Bichromatic Reading

1.           Read the plate at 450 nm against a reference filter set at 650 nm (or 630 nm).

2.           Calculate the mean of duplicate determinations.

3.           On semi-logarithmic or linear graph paper plot the OD values (ordinate) for each calibrator against the corresponding concentration of Calcitonin (abscissa) and draw a calibration curve through the calibrator points by connecting the plotted points with straight lines.

4.           Read the concentration for each control and sample by interpolation on the calibration curve. 

5.           Computer assisted data reduction will simplify these calculations.  If automatic result processing is used, a 4-parameter logistic function curve fitting is recommended.

11.     TYPICAL DATA

The following data are for illustration only and should never be used instead of the real time calibration curve.

12.     PERFORMANCE  AND  LIMITATIONS

A.       Detection Limit

Twenty zero calibrators were assayed along with a set of other calibrators. The detection limit, defined as the apparent concentration two standard deviations above the average OD at zero binding, was 0.5 pg/ml.

B.      Specificity

Some potentially interfering hormones have been tested in this assay.  At concentrations up to 100 ng/ml, none of the following hormones showed significant interference :

-    CGRP

-    Salmon-calcitonin

-    PDN 21

-    Procalcitonin N terminal.

C.      Precision

SD : Standard Deviation; CV: Coefficient of variation

D.       Accuracy     

                                             RECOVERY  TEST

Samples were diluted with CT Free Serum.

E.       Hook effect

A sample spiked with CT up to 830000 pg/ml gives higher OD’s than the last calibrator point.

13      INTERNAL  QUALITY  CONTROL

§             If the results obtained for Control 1 and/or Control 2 are not within the range specified on the vial label, the results cannot be used unless a satisfactory explanation for the discrepancy has been given.

§             If desirable, each laboratory can make its own pools of control samples, which should be kept frozen in aliquots. Controls which contain azide will interfere with the enzymatic reaction and cannot be used.

§             Acceptance criteria for the difference between the duplo results of the samples should rely on Good Laboratory Practises

§             It is recommended that Controls be routinely assayed as unknown samples to measure assay variability.  The performance of the assay should be monitored with quality control charts of the controls.

§             It is good practise to check visually the curve fit selected by the computer.

  14.     REFERENCE  INTERVALS

These values are given only for guidance; each laboratory should establish its own normal range of values.

Normal values

20 samples from normal subjects obtained values below 11 pg/ml.

Pentagastrin test:

Patient with MTC with elevated base levels of CT:  to verify

15.     PRECAUTIONS  AND  WARNINGS

Safety

For in vitro diagnostic use only.

The human blood components included in this kit have been tested by European approved and/or FDA approved methods and found negative for HBsAg, anti-HCV, anti-HIV-1 and 2.  No known method can offer complete assurance that human blood derivatives will not transmit hepatitis, AIDS or other infections.  Therefore, handling of reagents, serum or plasma specimens should be in accordance with local safety procedures.

All animal products and derivatives have been collected from healthy animals. Bovine components originate from countries where BSE has not been reported. Nevertheless, components containing animal substances should be treated as potentially infectious.

Avoid any skin contact with all reagents,  Stop Solution contains HCl, the chromogenic solution contains TMB and H₂O₂.   In case of contact, wash thoroughly with water.

Do not smoke, drink, eat or apply cosmetics in the working area.  Do not pipette by mouth.  Use protective clothing and disposable gloves. 

16      BIBLIOGRAPHY

1.       GRAZE K., SPILER I.J., TASHIJAN A.H., MELVIN K.E.W., CERVI-SKINNER S., GAGEL R.F., MILLER H.H., WOLFE H.J., DELELLIS R.A., LEAPE L., FELDMAN Z.T. and REICHLIN S.  (1978)

Natural history of familial medullary thyroid carcinoma; Effect of a program for early diagnosis.

Engl. J. Med., 299,18;980-985.

2.       HENNESSY J.F., WELLS S.A., ONTJES D.A. and COOPER C.W.  (1974)

A comparison of pentagastrin injection and calcium infusion as provocative agents for the detection of medullary carcinoma of the thyroid.

J. Clin. Endocrinol. Metab., 39:487-495.

3.       ROUGIER Ph., CALMETTES C., LAPLANCHE A., TRAVAGLI J.P., LEFEVRE M., PARMENTIER C., MILHAUD G. and TUBIANA M.  (1983)

the values of calcitonin and carcinoembryonic antigen in the treatment and management of nonfamilial medullary thyroid carcinoma.

          Cancer, 51,5:856-862.

4.       WALLACH S.R., ROYSTON I.,  TAETLE R., WOHL H. and DEFTOS        L.  (1981)

Plasma calcitonin as a marker of disease activity in patients with small cell carcinoma of the lung.

J. Clin. Endocrinol. Metab., 53,3:602-606.

5.       WELLS S.A., BAYLIN S.B., LINEHAN W.M., FARRELL R.E., COX E.B. and COOPER C.W.  (1978)

        Provocative agents and the diagnosis of medullary carcinoma of the thyroid            gland.

Ann. Surg., 188,2:139-141.

6.       AURBACH G.D., MARX S.J. and SPIEGEL A.M.  (1985)

Parathyroid hormone, calcitonin, and the calciferols.

In: williams Textbook of endocrinology (7th edition; Wilson J.D. and foster D.W. eds) W.B. Saunders Company, Philadelphia, 1137-1217.

7.       BODY J.J. et al.  (1987)

SCC antigen and other tumor markers in lung cancer: preliminary results.

Excerpta Medica, 162-170.

8.       NICOLI P. et al.  (1995)

Abnormal calcitonin basal levels and pentagastrin response in patients with chronic renal failure on maintenance hemodialysis. 

Eur. J. Endocrinol. 132, 1, 75-81.

9.       PACINI F. et al.  (1994)

Routine measurement of serum calcitonin in modular disease allows the preoperative diagnosis of unsuspected sporadic medullary thyroid carcinoma. 

J. Clin. Endocrinol. Metab. Excerpta Medica, 78, 4, 824-9.

10.     QUESADA J. M. et al. (1994)

Calcitriol corrects deficient calcitonin secretion in the Vit. D deficient elderly.

J. Bone Miner Res. 9, 1, 53-57.

17            SUMMARY OF THE PROTOCOL