A patient's blood glucose is 180mg/dL and after treatment drops to 135mg/dL. What is the percentage decrease?

Step 1: Identify the initial and final blood glucose levels. The initial blood glucose level is $180 \text{ mg/dL}$. The final blood glucose level after treatment is $135 \text{ mg/dL}$.

Step 2: Calculate the absolute decrease in blood glucose. $\text{Decrease} = Initial Value - \text{Final Value}$ $\text{Decrease} = 180 mg/dL - 135 \text{ mg/dL}$ $\text{Decrease} = 45 \text{ mg/dL}$

Step 3: Calculate the percentage decrease. $\text{Percentage Decrease} = \frac{Decrease}{Initial Value} \times 100\%$ $\text{Percentage Decrease} = \frac{45 mg/dL}{180 mg/dL} \times 100\%$ $\text{Percentage Decrease} = \frac{1}{4} \times 100\%$ $\text{Percentage Decrease} = 0.25 \times 100\%$ $\text{Percentage Decrease} = 25\%$

The percentage decrease in blood glucose is: $\boxed{25\%}$