Reverse T3 (rT3) is an inactive metabolite of thyroxine (T4). It is generated when T4 is converted by type 3 deiodinase (D3) rather than being transformed into the biologically active form of T3. Unlike T3, rT3 does not activate thyroid hormone receptors and therefore has no metabolic activity.

Measurement of rT3 is useful for determining whether thyroid hormone is being shunted away from active metabolism during periods of physiological stress or illness. Clinically, elevated rT3 levels are commonly observed in severe or chronic illness (such as infection, trauma, or surgery), starvation or very low-calorie diets, chronic inflammation, liver or kidney disease, and with certain medications (e.g., corticosteroids and amiodarone). In contrast, low rT3 levels are generally not clinically significant when interpreted on their own.

The RayBio^® Reverse T3 Enzyme Immunoassay (EIA) Kit is a competitive immunoassay that quantifies T3 (rT3) in serum or plasma from human, mouse, rat, porcine, feline, canine, equine, and sheep samples, as well as in urine samples, within 2.5 hours. Absorbance is measured at 450 nm and values are interpolated from a ready-to-use rT3 standard curve. The assay demonstrates a sensitivity of 0.042 ng/dL and has been validated for linearity, stability, precision, and spike-recovery performance. Each kit provides sufficient reagents to perform up to 96 assays, including the standard curve and unknown samples.

• Various species
• High sensitivity
• Rapid detection within 2.5 hours
• Good characteristics in terms of linearity, stability, precision, and spiking & recovery

• Pre-Coated 96-well Strip Microplate
• Assay Diluent
• Lyophilized Standard
• Positive Control
• Capture Antibody
• HRP-conjugated Secondary Antibody
• Wash Buffer
• TMB One-Step Substrate Reagent
• Stop Solution

• Microplate reader capable of measuring absorbance at 450 nm
• Precision pipettes to deliver 2 μL to 1 mL volumes
• Adjustable 1-25 mL pipettes for reagent preparation
• 100 mL and 1-liter graduated cylinders
• Distilled or deionized water
• Tubes to prepare standard or sample dilutions
• Orbital shaker
• Software which can perform four-parameter logistic regression models

1. Prepare all reagents, samples and standards as instructed.
2. Add 50 µL standards or samples to appropriate well. Incubate for 10 minutes at room temperature.
3. Add 50 µL Capture Antibody to appropriate well. Incubate 1 hour at room temperature. And wash 5 times.
4. Add 100 µL prepared HRP-Secondary Antibody solution. Incubate 1 hour at room temperature. And wash 5 times.
5. Add 100 µL TMB One-Step Substrate Reagent to each well. Incubate 5-20 minutes at room temperature.
6. Add 50 µL Stop Solution to each well. Read at 450 nm immediately.