Which type of specimen is usually collected for glucose tolerance testing?

For glucose tolerance testing, blood samples are essential because they allow for the direct measurement of glucose levels in the bloodstream. During the test, a patient undergoes a fasting period followed by the ingestion of a glucose solution. Subsequently, blood samples are taken at specific intervals to monitor how the body processes the glucose over time. This enables healthcare providers to assess the patient's insulin response and diagnose conditions such as diabetes or insulin resistance.

Other specimen types mentioned in the options would not provide the precise measurement needed for glucose tolerance testing. Urine samples do not directly reflect blood glucose levels in real time, and saliva samples lack the accuracy and reliability necessary for such testing. Capillary blood samples from the fingertip can be useful for quick glucose checks but are not typically used for formal glucose tolerance testing, which requires more standardized blood collection methods.