Chapter 12: Laboratory Diagnosis: Urine Studies

INTRODUCTION

COLLECTING URINE SAMPLES

(See also Urinary Tract Procedures, Chapter 19.)

• Random urine samples: These are collected at any time and are the most common for routine urinalysis.

• Midstream clean catch urine: Preferred for routine urine culture and sensitivity. Patients first cleanse the urethral area with a castile soap towelette or other provided wipe. The first portion of the urine stream goes into the toilet, and the midstream sample is captured in a sterile specimen cup. This technique reduces the number of contaminants that enter the sample.

• First morning specimen: Considered to be the urine specimen to give the most reliable urinalysis results. Patient voids before bedtime and then provides the morning sample upon awakening. Theoretically, this allows urine to concentrate elements, best for protein determinations and pregnancy testing. Often used to optimize the urinary detection of tuberculosis (TB).

• Timed sample collection: Used to collect urine over a specific period (e.g., 8 hr; 24 hr) to measure analytes such as creatinine, calcium, oxalate, catecholamines, and 17-hydroxysteroids that are affected by diurnal variations. Many require sample to be kept on ice.

• Catheter collection: In patients unable to void, an “in and out” bladder catheter technique can be used (see Urinary Tract Procedures, Chapter 19). In the setting of a chronic indwelling catheter, the sample must not be obtained from the collection bag and should be directly obtained from the catheter. In patients with urostomy, the stoma should be catheterized to collect the sample and not the collection bag.

• Suprapubic bladder aspiration can be performed in infants and children and very selectively in adults. External introduction of a needle through the abdomen into the bladder is sterile under normal conditions when cultured. See Chapter 19, Percutaneous Suprapubic Bladder Aspiration.

• Pediatric samples are often collected using a pediatric sterile urine collection bag applied to the skin around the urethra.

HANDLING THE URINE SPECIMEN

• For routine urinalysis (UA), a fresh (less than 2 hr old), clean catch urine sample is preferred. If the analysis cannot be performed immediately, refrigerate the sample (2–8°C) or collect the sample in a preservative-containing tube described below. If refrigerated, rewarm to room temperature just prior to assessment (Note: When urine stands at room temperature for a long time, casts and red cells undergo lysis, and the urine becomes alkalinized with precipitation of salts).

• A variety of urine collection and transfer products are now available to protect healthcare personnel and protect the specimen from contamination. One brand of a ...