What is measured by a blood test after a person has had nothing to eat or drink for a period of time?

A fasting blood sugar test measures the concentration of glucose in the blood after an individual has refrained from eating or drinking for a specific period, typically 8 to 12 hours. This fasting state is critical because it allows for an accurate assessment of the body’s baseline blood sugar level without the influence of food intake. Elevated fasting blood sugar levels can indicate conditions such as diabetes or prediabetes, making this test an important diagnostic tool for assessing metabolic health.

Other options listed could be relevant in different contexts, but they do not specifically require fasting for accurate measurement. Cholesterol levels can be measured at any time, although fasting can sometimes provide more reliable readings. Blood pressure and electrolyte balance tests can be performed without requiring fasting conditions. Thus, the specific requirement for fasting is what makes fasting blood sugar the correct answer.