Which single-letter abbreviation is used to denote decrease or decreased?

• A. D
• B. T
• C. Δ
• D. ↓

Answer: (B)

The key idea is recognizing how direction of change is often communicated in clinical notation with compact symbols. In this context, a single letter used to indicate a downward change is the letter T, which stands for a downward trend or decrease over time. It signals that the value is moving lower, rather than just noting that a change occurred. This differs from the other options: the downward arrow is a graphical indicator rather than a letter, Δ denotes change in value (magnitude) without specifying direction, and the other letters don’t carry the same shorthand meaning for a downward trend in this testing context. So the choice that uses the letter for a downward trend is the one that best fits the idea of “decrease” as a concise notation.