What makes a biomarker assay trustworthy?

Precision asks whether the result repeats

An assay should produce sufficiently consistent results when the same sample is measured repeatedly. Developers examine within-run precision, variation across days, operators, instruments, and reagent or cartridge lots.

Precision is concentration-dependent. Performance near the low end of a measurement range can differ from performance in the middle, which matters for salivary testosterone because concentrations are small.

Selectivity asks what else changes the signal

A biological sample contains many molecules besides the target. Interference studies evaluate whether related hormones, medications, food residue, blood contamination, oral-health conditions, or sample chemistry distort the measurement.

Collection devices, storage time, temperature, and user technique also need testing. A convenient protocol is useful only when ordinary real-world variation is understood and controlled.

• Repeatability and reproducibility
• Analytical range and detection limits
• Interference and cross-reactivity
• Sample and reagent stability
• Agreement with an appropriate reference method

Validation follows the intended use

A study can show that two measurements move together without proving that either is accurate enough for diagnosis. The evidence required for an exploratory wellness pattern signal is different from the evidence required for a clinical decision.

Axis is still in the development stage. The responsible path is to define the intended use narrowly, publish the validation plan, report limitations, and avoid performance claims until the necessary data exist.