The DSL-10-671000 ACTIVE Cortisol Enzyme Immunoassay (EIA) Kit provides materials for the quantitative measurement of cortisol in saliva.
NORTH AMERICAN CUSTOMERS ONLY:
This assay is intended for research use only and not for use in diagnostic procedures. For use only by researchers and laboratories certified by Diagnostic Systems Laboratories, Inc., 445 Medical Center Blvd., Webster, TX 77598.
II. SUMMARY AND EXPLANATION OF THE TEST
Cortisol (hydrocortisone, compound F) is the most potent glucocorticoid produced by the human adrenal cortex. As with other adrenal steroids, cortisol is synthesized from cholesterol through a series of enzymatically mediated steps [reviewed in 1,2]. The first and rate-limiting step in adrenal steroidogenesis, conversion of cholesterol to pregnenolone, is stimulated by pituitary adrenocorticotropic hormone (ACTH) which is, in turn, regulated by hypothalamic corticotropin releasing factor (CRF). ACTH and CRF secretion are inhibited by high cortisol levels. In plasma, the major portion of cortisol is bound with high affinity to corticosteroid-binding globulin (CBG, transcortin), with most of the remainder loosely bound to albumin. Cortisol acts through specific intracellular receptors and has effects in numerous physiologic systems, including immune function, glucose-counterregulation, vascular tone, substrate utilization and bone metabolism
[1-3]. Cortisol is excreted primarily in urine in an unbound (free) form. Salivary cortisol measurement is an excellent indicator of free cortisol or biologically active cortisol in human serum [4, 5].
The measurement of cortisol in saliva provides several advantages over its measurement in serum or plasma. First, sample collection for salivary cortisol measurement is noninvasive and inexpensive, and specimen collection is easy to perform in infants and children [6, 7]. Second, multiple samples may be collected at home thus offering a convenient way to collect a series of samples at different times of the day .
Cortisol production has an ACTH-dependent circadian rhythm with peak levels in the early morning and a nadir at night. The factors controlling this circadian rhythm are not completely defined. The circadian rhythm of ACTH/cortisol secretion matures gradually during early infancy, and is disrupted in a number of physical and psychological conditions . Furthermore, increased amounts of ACTH and cortisol are secreted independently of the circadian rhythm in response to physical and psychological stress [8, 9].
The DSL-10-67100 ACTIVE Cortisol EIA Kit uses a specific rabbit anti-cortisol antibody, and does not require prior sample extraction of saliva. Cross-reactivity to other naturally occurring steroids is low.
III. PRINCIPLE OF THE TEST
The procedure follows the basic principle of enzyme immunoassay where there is competition between an unlabeled antigen and an enzyme-labeled antigen for a fixed number of antibody binding sites. The amount of enzyme-labeled antigen bound to the antibody is inversely proportional to the concentration of the unlabeled analyte present. Unbound materials are removed by decanting and washing the wells.
The DSL-10-67100 ACTIVE Cortisol EIA Kit contains sufficient reagents for 96 wells. Each kit contains the following reagents:
A. GARG-Coated Microtitration Strips:
One stripholder, containing 96 polystyrene microtiter wells with goat anti-rabbit globulin serum immobilized to the inside wall of each well. Store at 2-8C until expiration date in the resealable pouch with a desiccant to protect from moisture.
B. Cortisol Antiserum:
One vial, 11 mL, containing rabbit anti-cortisol serum in a protein-based (BSA) buffer with a non-mercury preservative. Store unopened at 2-8 °C until expiration date. Store opened vials at 2-8C for up to 3 weeks.
C. Cortisol Standards:
Eight vials, 0.5 mL each, labeled A-H, containing concentrations of approximately 0, 0.1, 0.5, 1.5, 4.0, and 10.0 g/dL cortisol in a protein-based (BSA) buffer with a non-mercury preservative. Refer to vial labels for exact concentrations. Store unopened at 2-8C until expiration date. Store opened vials at 2-8C for up to 3 weeks. For longer periods, store at
-20C or lower until expiration date.
D. Cortisol Controls:
Two vials, 0.5 mL each, Levels I and II, containing low and high concentrations of cortisol in a protein-based (BSA) buffer with a non-mercury preservative. Store unopened at 2-8C until expiration date. Store opened vials at 2-8C for up to 3 weeks. For longer periods, store at
-20C or lower until expiration date.
E. Cortisol Enzyme Conjugate Concentrate:
One vial, containing 0.3 mL of a solution of cortisol conjugated to horseradish peroxidase in a protein-based buffer (BSA) with a non-mercury preservative. Dilute prior to use in Conjugate Diluent. Store at 2-8C until expiration date.
F. Conjugate Diluent:
One bottle, 11 mL, containing a protein-based buffer (BSA) with a non-mercury preservative. Store at 2-8C until expiration date.
G. TMB Chromogen Solution:
One bottle, 11 mL, containing a solution of tetramethylbenzidine (TMB) in citrate buffer with hydrogen peroxide. Store at 2-8C until expiration date.
H. Wash Concentrate:
One bottle, 100 mL, containing buffered saline with a nonionic detergent. Dilute 10-fold with deionized water prior to use. Store unopened at room temperature or 2-8C until expiration date.
I. Stopping Solution:
One vial, 11mL, containing 0.2M sulfuric acid. Store at 2-8C until expiration date.
NOTE: All reagents and samples must be allowed to reach room temperature (~25 C) and mixed thoroughly by gentle inversion before use.
For in vitro use.
The following precautions should be observed in the laboratory:
Do not eat, drink, smoke or apply cosmetics where immunodiagnostic materials are being handled.
Do not pipet by mouth.
Wear gloves when handling immunodiagnostic materials and wash hands thoroughly afterwards.
Cover working area with disposable absorbent paper.
WARNING: POTENTIAL BIOHAZARDOUS MATERIAL
This kit may contain reagents made with human serum or plasma. The serum or plasma used has been tested by an FDA-approved method and found to be non-reactive for HIV-1/2 Antibodies HCV and HBsAg. Because no method can offer complete assurance that HIV-1/2, HCV, HBsAg or other infectious agents are absent, these reagents should be handled at the Biosafety Level 2 as recommended for any potentially infectious human serum or blood specimen in the Centers for Disease Control/National Institutes of Health manual "Biosafety in Microbiological and Biomedical Laboratories," 3rd Edition, 1993.
Avoid contact with reagents containing TMB, hydrogen peroxide, or sulfuric acid. TMB is dissolved in a solution which contains dimethylformamide, an irritant to skin and mucous membranes. In case of contact with any of these reagents, wash thoroughly with water.
TMB is a suspected carcinogen.
VI. SPECIMEN COLLECTION AND PREPARATION
It is recommended that saliva should be collected with the SARSTEDT SALIVETTE. The SALIVETTE is centrifuged for two minutes at 1000 xg. During centrifugation, the saliva will pass from the cylindrical shaped swab through the hole in the bottom of the suspended tube into the clear centrifuge tube. Mucous strands and particles will be caught in the conical tip of the centrifuge tube allowing easy decanting of the clear saliva.
VII. PROCEDURAL NOTES
A thorough understanding of this package insert is necessary for successful use of the product. Reliable results will only be obtained by using precise laboratory techniques and accurately following the package insert. A standard curve must be included with each assay.
Bring all kit reagents and specimens to room temperature (~25C) before use. Thoroughly mix the reagents and samples before use by gentle inversion.
Do not mix various lots of any kit component within an individual assay. Do not use any component beyond the expiration date shown on its label.
Incomplete washing will adversely affect the outcome and assay precision.
To minimize potential assay drift due to variation in the substrate incubation time, care should be taken to add the stopping solution into the wells in the same order and speed used to add the TMB Chromogen Solution.
Avoid microbial contamination of reagents, especially of the conjugate concentrate and the conjugate diluent. Avoid contamination of the TMB Chromogen Solution with the Enzyme Conjugate. Use a clean disposable pipette tip for each reagent, Standard, Control or specimen. For dispensing sulfuric acid and TMB Chromogen Solution, avoid pipettes with metal parts.
Containers and semi-automatic pipette tips used for the Enzyme Conjugate Solution and the TMB Chromogen Solution can be reused provided they are thoroughly rinsed with distilled water prior to and after each usage.
The enzyme used as the label is inactivated by oxygen, and is highly sensitive to microbial contamination, sodium azide, hypochlorous acid and aromatic chlorohydrocarbons often found in laboratory water supplies. Use high quality water.
Avoid exposure of the reagents to excessive heat or direct sunlight during storage and incubation.
Microtitration plate reader capable of absorbance measurement at 450 nm and preferentially capable of dual wavelength correction at 600 or 620 nm.
Precision pipette to deliver 25 L and 220 L.
Semi-automatic pipette to deliver 100 L and 200 L.
Microtitration plate shaker capable of 500-700 orbital revolutions per minute (rpm).
Automatic microtitration plate washer.
Absorbent materials for blotting the strips.
Linear-log graph paper for manual data reduction.
C. Preparation of Reagents:
1. Wash Solution
Prepare Wash Solution by diluting Wash Concentrate 10-fold with deionized water in a suitable container. Store in a tightly sealed bottle at room temperature for up to one month.
2. Enzyme Conjugate Solution
The Enzyme Conjugate Concentrate should be diluted at a ratio of 1 part Cortisol Enzyme Conjugate Concentrate into 50 parts Conjugate Diluent, according to the number of wells used. If an entire plate is to be used, pipet exactly 220 L of the Cortisol Enzyme Conjugate Concentrate into 11 mL of the Conjugate Diluent. The Cortisol Enzyme Conjugate Solution should be prepared just prior to use in the assay.
3. Microtitration Wells
Select the number of coated wells required for the assay. The remaining unused wells should be placed in the resealable pouch with a desiccant. The pouch must be resealed to protect from moisture.
D. Assay Procedure:
Allow all specimens and reagents to reach room temperature (~25C) and mix liquid reagents thoroughly by gentle inversion before use. Standards, Controls and unknowns should be assayed in duplicate.
1. Mark the microtitration strips to be used.
2. Prepare the Enzyme Conjugate Solution by diluting the Conjugate in the Conjugate Diluent as described under the Preparation of the Reagents section of this package insert.
3. Pipet 25 L of each Standard, Control and unknown into the appropriate wells.
4. Add 100 L of the Enzyme Conjugate Solution to each well using a semi-automatic dispenser. Gently tap the well holder for 5-10 seconds.
5. Add 100 L of the Cortisol Antiserum to each well using a semi-automatic dispenser.
6. Incubate the wells at room temperature (~25C) on a shaker set at 500 - 700 rpm for 45 minutes.
7. Aspirate and wash each well 5 times with the Wash Solution using an automatic microplate washer. Blot dry by inverting plate on absorbent material.
NOTE: Use of an automatic microplate washer is strongly recommended. Incomplete washing will adversely affect assay precision. If a microplate washer is not available, (a) completely aspirate the liquid from each well, (b) dispense 0.35 mL of the Wash Solution into each well, and (c) repeat steps (a) and (b) five times. 8. Add 100 L of the TMB Chromogen Solution to each well using a semi-automatic dispenser.
Incubate the wells at room temperature (~25°C) for 10-15 minutes on an orbital microplate shaker set at 500 - 700 rpm. Avoid exposure to direct sunlight.
NOTE: Please be aware that the color may develop more quickly or more slowly than the recommended incubation time depending on the localized room temperature. Please visually monitor the color development to optimize the incubation time. 10. Add 100 L of the Stopping Solution to each well using a semi-automatic dispenser.
11. Shake the plate by hand for 5-10 seconds.
12. Read the absorbance of the solution in the wells within 30 minutes, using a microplate reader set to 450 nm.
NOTE: If wavelength correction is available, set the instrument to dual wavelength measurement at 450 nm with background wavelength correction set at 600 or 620 nm.
IX. CALCULATION OF RESULTS
A. Calculate the mean absorbance for each Standard, Control or unknown.
B. Using a linear-log graph paper, plot the mean absorbance readings for each of the standards along the y-axis versus the cortisol concentrations in g/dL along the x-axis. Alternatively, any data reduction software designed for immunoassays could be used. Four-parameter curve-fit is recommended.
C. Draw the best fitting curve through the mean of the duplicate points.
D. Determine the cortisol concentrations of the Controls and unknowns from the standard curve by matching their mean absorbance readings with the corresponding cortisol concentrations.
E. Any sample reading higher than the highest Standard should be appropriately diluted with the 0 g/dL Standard and reassayed.
F. Multiply the value by the dilution factor if required.
If the absorbance readings exceed the limitation of the plate reader, a second reading at 405 nm is needed (reference filter 600 or 620 if available). In this case, proceed to construct a second standard curve as above with the absorbance readings of all Standards at 405 nm. The concentration of the off-scale samples at 450 nm are then read from the new standard curve. The readings at 405 nm should not replace the on-scale readings at 450 nm.
The reagents supplied in this kit are optimized to measure cortisol levels in saliva.
Avoid repeated freezing and thawing of reagents and specimens.
Hemolyzed, icteric or lipemic specimens may give false values and should not be used.
The DSL Controls or other commercial controls should fall within established confidence limits. The confidence limits for the DSL Controls are printed on the Control vial labels.
Low and high level Controls should be included in each assay.
The TMB Chromogen Solution should be colorless. Development of a blue color may indicate reagent contamination or instability.
TYPICAL ACTIVE CORTISOL EIA STANDARD CURVE DATA
CAUTION: The above data must not be employed in lieu of data obtained by the user in the laboratory.
XII. PERFORMANCE CHARACTERISTICS
All performance characteristics are stated in g/dL. To convert to nmol/L:
g/dL x 27.6 = nmol/L
The theoretical sensitivity or minimum detection limit, calculated by the interpolation of the mean minus two standard deviations of twenty-one replicates of the 0 g/dL Cortisol Standard, is 0.072 g/dL.
The intra-assay precision was determined from the mean of 16 replicates each.
The inter-assay precision was determined from the mean of average duplicates for 10 separate runs.
Three saliva samples containing different levels of endogenous cortisol were spiked with known amounts of cortisol and assayed.
Two saliva samples were diluted with the 0 g/dL Cortisol Standard and assayed.
The cross-reactivity of the cortisol antiserum has been measured against various compounds. The percent cross-reactivity is expressed as the ratio of the cortisol concentration to the concentration of the reacting compound at 50% binding of the 0 g/dL Cortisol Standard.
The DSL ACTIVE salivary Cortisol EIA was compared to another commercially available cortisol RIA kit (Method A) by assaying 21 saliva samples ranging from 4.10 to 30.16 g/dL (EIA). The regression analysis yielded the following equation:
[DSL-10-67100]= 0.13 [Method A] + 0.12
r = 0.95
1. Drucker S, New MI: Disorders of adrenal steroidogenesis. Pediatr Clin North Am 34:1055-1066, 1987.
2. Migeon CJ, Lanes RL: Adrenal cortex: hypo- and hyperfunction. IN Lifshitz F (ed): Pediatric Endocrinology, A Clinical Guide, second edition. Marcel Dekker, Inc., New York, 1990, pp. 333-352.
Hyams JS, Carey DE: Corticosteroids and growth. J Pediatr 113:249-254, 1988.