Collection and preservation of urine for analytical testing

must follow a carefully prescribed procedure to ensure valid results. Laboratory testing of urine generally falls

under three categories, example, chemical, bacteriologic, and microscopic examination. There are also three kinds

of collection for urine specimens, first random, second timed, and third 24-hour total volume. Random specimens may

be collected any time, but a first morning voided aliquot is optimal for constituent concentration. Laboratory

results from a random urine collection are expressed per unit volume if the result is a quantitative analysis.

Result reporting of a random collection is expressed as positive or negative, indicating the presence or absence of

a particular constituent, such as glucose. Random urine specimens should be collected in a chemically clean

receptacle, either glass or plastic. A clean-catch midstream specimen is most desirable for bacteriologic

examinations using medical microscopes. The vessel is tightly sealed, labeled with the patient’s name

and date of collection, and submitted for analysis. A first morning urine specimen is generally the most

concentrated and considered a better specimen for evaluation. Timed specimens are obtained at designated intervals,

starting from time zero, and are noted on each subsequent container time of collection. Urine specimens for a 24-

hour total volume collection are most difficult to obtain and require cooperation from the patient. Incomplete

collection is the major problem.

In some instances, over collection occurs. Because in-hospital collection

is usually under the supervision of the nursing staff, it is more reliable than outpatient collections. Collection

of urine specimens from pediatric patients requires special attention to avoid contamination from the stool. One

can avoid problems by giving patients complete written and verbal instructions with a warning that the test can be

invalidated by incorrect collection technique. If specimen is to be collected on an outpatient basis, exercise care

and instruct patient’s parents to keep the specimen out of the reach of children, especially if concentrated acid

is used as a preservative. An unbreakable, 4 L approximately plastic, chemically clean container with the correct

preservative already added is preferred. One should remind the patient to discard the first morning specimen,

record the time, and collect every subsequent voiding for the next 24 hours, with the last to be 24 hours after

timing commenced. Over collection occurs if the first morning specimen is included in this routine. Measure the

total volume collected, record the information on the request form, thoroughly mix the entire 24-hour collection,

and submit for analysis. A 40-mL aliquot is adequate for this purpose. Completeness of collection is difficult to

determine.

If results appear clinically invalid when examined under a medical microscope, this is cause for

suspicion. Because creatinine excretion is based on muscle mass, and because a patient’s muscle mass is relatively

constant, creatinine excretion is also reasonably constant. Therefore, one should measure creatinine on several 24

-hour collections and keep this as part of the patient’s record. Another approach is to express results relative

to the concentration of creatinine when collecting a specimen other than a 24-hour one. One and two-hour timed

collection specimens may suffice in some instances.

SPECIAL URINE COLLECTION

TECHNIQUES

Catheterization of the bladder may cause infection but is necessary in some patients.

Catheterization also is used for urine collection when patients are unable to void or control micturition.

Suprapubic aspiration is performed with a syringe and needle above the symphysis pubis, through the abdominal wall,

into a full bladder. This method is used to obtain otherwise problematic anaerobic cultures. Ureteral catheters are

inserted via a cystoscope into the ureter. Bladder urine is collected first, followed by a bladder washing.

Ureteral urine specimens are useful in differentiating bladder from kidney infection or for differential ureteral

analysis using medical microscopes, and may be obtained separately from each kidney pelvis labeled left and right.

First morning urine samples for cytologic examination are optimal.