Tetramethylbenzidine (TMB) substrate reaction rate in serum/plasma (immunoassay-based chemiluminescent or enzymatic endpoint)

What This Test Measures

TMB is a colorless compound that changes color when it reacts with enzymes or antibodies in a lab test. This test specifically tracks the rate of this color change, which reflects the activity level of the underlying biochemical process. For example, it may be used in assays for detecting or quantifying substances like hormones, proteins, or enzymes that trigger this reaction.

Common Uses in Medical Testing

TMB reaction rates are often part of broader immunoassays (e.g., for thyroid hormones, pregnancy tests, or autoimmune markers) or enzymatic assays (e.g., for liver enzymes or metabolic markers). Your doctor may order this test indirectly to support other tests, such as checking for thyroid function, inflammation, or infection.

How the Test Works

A small sample of your blood (serum or plasma) is mixed with TMB and a catalyst (like an enzyme or antibody). The reaction produces a measurable change over time, which the lab analyzes to determine the rate. This rate can indicate the presence or concentration of the target substance in your blood.

Preparation for the Test

No special preparation is needed for this test. You may fast or take medications as usual unless instructed otherwise. If you’re taking blood thinners, let your doctor know before the test.