Which of the following is a strong reducing agent that can affect glucose testing?

Ascorbic acid, also known as Vitamin C, is a strong reducing agent that can interfere with glucose testing methods, particularly those that use glucose oxidase. In these tests, glucose oxidase catalyzes the oxidation of glucose, producing hydrogen peroxide and gluconic acid. The presence of ascorbic acid can reduce the hydrogen peroxide back to water, effectively decreasing the detectable signal of glucose, leading to false-negative results.

In laboratory settings, the reducing properties of ascorbic acid can complicate accurate glucose measurements by either directly or indirectly impacting the enzymatic reactions involved in glucose testing. Because it donates electrons readily, it can interfere with colorimetric assays that are based on color change, which is often how glucose levels are quantified.

The other substances listed do not have the same level of interaction with glucose testing methodologies. Peroxide would generally be a product of the glucose reaction rather than an interfering substance. Sodium nitroprusside is typically associated with testing for ketones and does not impact glucose testing directly. Calcium chloride is used in various biochemical applications but does not exhibit reducing properties that affect glucose assays. Therefore, ascorbic acid stands out as the agent that significantly impacts glucose test accuracy.