TDT Test (Tone Decay Test)

The tone decay test (TDT) assesses auditory nerve function by presenting a continuous pure tone at or near hearing threshold and asking the patient whether it fades over about 10 seconds. Rapid or marked tone decay—loss of perception during the stimulus—suggests retrocochlear pathology (auditory nerve/brainstem lesion), whereas little or no decay is more consistent with normal hearing or cochlear (sensory) loss.

The tone-decay test measures whether a pure tone presented at the patient’s hearing threshold can be heard continuously for up to 60 seconds. If the tone fades and the threshold rises markedly (usually >10 dB), that’s a positive decay suggesting retrocochlear dysfunction. In Meniere’s disease (a cochlear disorder) tone decay is typically absent or only minimal, helping distinguish it from nerve lesions.

The TDT (Tone Decay Test) assesses retrocochlear auditory function by presenting a continuous pure tone above the hearing threshold and noting whether perceived loudness fades over time. Rapid decay or need to increase intensity suggests neural pathology (for example, acoustic neuroma) rather than isolated cochlear loss. It is a screening tool and not definitive on its own.

Tone decay refers to the fading of a continuous pure tone presented just above hearing threshold. Minimal or no decay suggests normal cochlear function; significant or rapid decay (commonly >20 dB or fading within seconds) points to possible retrocochlear or auditory nerve pathology. It’s a screening sign — a positive result needs further objective testing (e.g., auditory brainstem testing, imaging) for diagnosis.

The TdT test detects terminal deoxynucleotidyl transferase, a nuclear enzyme found in immature lymphoid precursor cells. Performed by immunohistochemistry or flow cytometry on blood or bone marrow, it helps identify lymphoblasts in acute lymphoblastic leukemia (ALL) and distinguish lymphoid from myeloid blasts. A positive TdT supports ALL diagnosis and aids classification and treatment planning.

A decay test is a dental assessment to detect and evaluate tooth decay (dental caries). It combines visual examination, dental X‑rays and diagnostic tools (transillumination, laser fluorescence or probes) to locate cavities, assess lesion depth and activity, and estimate future risk. Results guide preventive measures (fluoride, sealants, diet) or treatments (fillings, root canal) depending on severity.