This is the most commonly requested specimen. Because the composition of urine changes over the course of the day, the time of day when the specimen is collected may influence the findings. The first voided morning specimen is particularly valuable because it is usually more concentrated and therefore more likely to reveal abnormalities as well as the presence of formed substances. It is also relatively free of dietary influences and of changes caused by physical activity because the specimen is collected after a period of fasting and rest.
Instruct the patient to void directly into a clean, dry container or bedpan. Transfer the specimen directly into an appropriate container. Disposable containers are recommended. Women should always have a clean-catch specimen if a microscopic examination is ordered (see Chapter 7).
Collect specimens from infants and young children into a disposable collection apparatus consisting of a plastic bag with an adhesive backing around the opening that can be fastened to the perineal area or around the penis to permit voiding directly into the bag. The specimen bag is carefully removed, and the urine is transferred to an appropriate specimen container.
Cover all specimens tightly; label properly with the patient’s name, date and time of collection, and test(s) ordered; and send immediately to the laboratory. Place the label on the cup, not on the lid.
Obtain a clean specimen using the same procedure as for bacteriologic examination (see Chapter 7) if a urine specimen is likely to be contaminated with drainage, vaginal discharge, or menstrual blood.
If a urine specimen is obtained from an indwelling catheter, it may be necessary to clamp off the catheter for about 15–30 minutes before obtaining the sample. Clean the specimen port in the tubing with antiseptic before aspirating the urine sample with a needle and syringe or a Luer-Lok syringe.
Observe standard precautions when handling urine specimens (see Appendix A).
If the specimen cannot be delivered to the laboratory or tested within 1 hour, it should be refrigerated or have an appropriate preservative added.
Feces, discharges, vaginal secretions, and menstrual blood will contaminate the urine specimen. A clean voided specimen must be obtained.
If the specimen is not refrigerated within 1 hour of collection, the following changes in composition may occur:
Increased pH from the breakdown of urea to ammonia by urease-producing bacteria
Decreased glucose from glycolysis and bacterial utilization
Decreased ketones because of volatilization
Decreased bilirubin from exposure to light
Decreased urobilinogen as a result of its oxidation to urobilin
Increased nitrite from bacterial reduction of nitrate
Increased bacteria from bacterial reproduction
Increased turbidity caused by bacterial growth and possible precipitation of amorphous material
Disintegration of red blood cells (RBCs) and casts, particularly in dilute alkaline urine
Changes in color caused by oxidation or reduction of metabolites