Which of the following describes an essential step before taking a midstream urine specimen?

Cleansing the perineum is a crucial step before taking a midstream urine specimen because it helps to reduce the risk of contamination in the sample. By thoroughly cleaning the area, any bacteria or debris that may be present around the genital region can be minimized, ensuring that the urine collected is more representative of the bladder contents rather than being tainted by external microorganisms. This is particularly important in clinical settings where accurate diagnosis and treatment plans depend on reliable test results.

The other options do not address the fundamental need for a clean sample. Asking the patient to void completely may result in the collection of a sample that doesn't accurately represent their urine at that moment, and pre-measuring urine volume is unnecessary for obtaining a midstream sample. Instructing the patient to drink more fluids may lead to diluted urine, which could also affect test results negatively. Therefore, cleansing the perineum stands out as the essential step directly related to obtaining a quality midstream specimen.