Human Free Thyroxine (fT4) ELISA Kit

What it means: Sandwich ELISA uses two antibodies targeting different epitopes of fT4: one captures the analyte, the other detects it. The signal is directly proportional to the amount of fT4 in the sample.

Why it matters:

• High specificity and sensitivity — ideal for complex biological matrices.
• Linear standard curve enables accurate quantification across a wide dynamic range.
• Gold-standard format trusted in peer-reviewed research and biomarker validation studies.

How to interpret here: This Sandwich ELISA is pre-optimized for quantifying fT4. Follow the kit protocol for sample dilution and standard preparation.

Tip: Sample matrix effects can alter recovery — always run at least one spiked recovery control to validate your specific matrix.

What it means: This kit is validated for use with serum as the primary sample matrix for fT4 quantification.

Why it matters:

• Sample matrix validation ensures the assay performs within its specified sensitivity and recovery range.
• Using non-validated matrices may introduce matrix interference, false-positive, or false-negative results.
• Sample preparation (dilution, pH adjustment) must be optimized for each matrix type.

How to interpret here: For this kit, serum is the primary validated matrix. If using other matrices, perform a spike-and-recovery experiment to verify performance before generating reportable data.

What it means: The assay sensitivity is 2.2 pmol/L — defined as the minimum detectable concentration of fT4 distinguishable from zero (typically the mean OD of blank ± 2 SD mapped to the standard curve).

Why it matters:

• Determines whether low-abundance fT4 in your specific sample type can be reliably detected.
• Samples with fT4 below this limit should be concentrated or the assay should be optimized.
• Sensitivity may vary slightly between lots — always refer to the lot-specific certificate of analysis.

How to interpret here: A sensitivity of 2.2 pmol/L means this kit can reliably detect fT4 at 2.2 pmol/L or above. Plan sample dilutions to ensure values fall within the detection range.

Tip: Do not extrapolate below the lowest standard — report as <2.2 pmol/L instead.

What it means: The quantitative working range of this assay is 4-64 pmol/L for fT4. Values outside this range cannot be accurately quantified.

Why it matters:

• Samples above the upper limit must be diluted before measurement; values below the lower limit are unreliable.
• Standard curves are validated within this range — interpolation is only valid within these bounds.
• Physiological concentrations of fT4 in your matrix should ideally fall in the mid-range for best precision.

How to interpret here: For fT4, the validated linear range is 4-64 pmol/L. Prepare a two-fold dilution series of samples to bracket expected concentrations within this range.

What it means: This kit is validated for detecting fT4 from Human biological samples. The capture and detection antibodies are raised and tested against Human-derived fT4 protein.

Why it matters:

• Cross-species reactivity is not guaranteed unless explicitly validated — using an incorrect species can produce false-negative results due to epitope differences.
• Sequence identity between species determines the likelihood of cross-reactivity.
• For studies requiring multiple species, confirm cross-reactivity data in the kit datasheet.

How to interpret here: This kit is designed and validated for Human samples. Contact technical support if you need to use samples from a different species not listed in the specification.

What it means: Total assay duration from sample addition to absorbance reading is approximately 3.5–5 hours, including incubation, wash, substrate development, and stop steps.

Why it matters:

• Plan your experiment schedule to complete the assay in a single session — stopping and restarting mid-protocol can affect results.
• Hands-on time is typically much shorter than total assay time — most steps are passive incubation.
• Temperature control during incubation is critical for reproducibility; use a plate shaker if specified.

How to interpret here: Schedule approximately 3.5–5 hours from sample plating to final read. Ensure all reagents are at room temperature before use.

What it means: This kit uses Colorimetric (TMB/HRP) detection — HRP enzyme conjugated to the detection antibody converts TMB substrate to a blue product (yellow after H₂SO₄ stop), measured at 450 nm on a standard microplate reader.

Why it matters:

• Colorimetric detection does not require specialized fluorescent readers — any standard 450 nm absorbance reader is compatible.
• TMB-HRP signal is stable for 30 minutes after the stop reaction — plan readings accordingly.
• Minimize light exposure after substrate addition to avoid photobleaching artifacts.

How to interpret here: Measure absorbance at 450 nm with a 570 nm or 630 nm reference wavelength to reduce background. Ensure the reader is calibrated and the plate is clean and free of condensation.