Urine Specimen Collection and Preservation Notes

Chapter 2: Urine Specimen Types, Collection, and Preservation

Learning Objectives

  • State at least three clinical reasons for performing a routine urinalysis.
  • Describe three types of urine specimens and state at least one diagnostic use for each type.
  • Explain the importance of accurate timing and complete collection of timed urine specimens.
  • Describe the collection technique used to obtain the following specimens:
    • Random void
    • Midstream "clean catch"
    • Catheterized
    • Suprapubic aspiration
    • Pediatric collection
  • Describe basic material and procedures used for proper collection and identification of urine specimens.
  • Identify at least six reasons for rejecting a urine specimen.
  • State changes possible in unpreserved urine and explain the mechanism for each.
  • Discuss urine preservatives and their uses.
  • List and justify at least three tests that assist in determining whether a fluid is urine.

Purposes of Routine Urine Analysis

  • Aid in disease diagnosis.
  • Screen for asymptomatic, congenital, or hereditary diseases.
  • Monitor disease progression.
  • Monitor therapy effectiveness or complications.
  • Vital to have written criteria for urine specimen types, instructions for proper collection and preservation, appropriate labeling, and a handling timeline.

Why Study Urine?

  • Urine analysis (UA) is a “fluid biopsy” of the kidney.
  • Noninvasive means to evaluate the kidney.
  • Specimens are usually readily available.
  • Urine is the ultrafiltrate of plasma.
  • Can be used to evaluate and monitor body homeostasis and many metabolic diseases.

Specimen Types

First Morning

  • Empty bladder at night before going to bed.
  • Collect specimen first thing in morning
  • Most concentrated; often preferred specimen.
  • Used for nitrites, protein, confirm postural or orthostatic proteinuria
  • Used for cytology studies
  • Formed elements such as white blood cells, red blood cells, and casts are stable due to high osmolality of first morning specimens.

Random

  • For routine screening; can be collected at any time
  • Can be affected by excess fluid intake or exercise, so may not accurately reflect a patient’s condition.
  • Ideal for cytology studies with prior hydration of the patient (24 to 32 oz of water each hour for 2 hours before urine collection); increases number of cells studied.

Timed Collection

  • Collections for a predetermined length of time, usually 12-hour or 24-hour.
  • Collections at a specified time of day (e.g., 2 pm to 4 pm).
  • Example is 4-hour or 12-hour specimen for determination of urine albumin, creatinine, and albumin-creatinine ratio.
  • Vital that the bladder is emptied and the first void is discarded at the beginning of a timed collection and to collect all urine subsequently passed during the collection period.
  • May need to add a preservation to ensure stability throughout the collection period.

Collection Techniques: Routine Void

  • Requires no patient preparation.
  • Collected by having patient void into appropriate container.
  • Patient normally needs no assistance other than clear directions.
  • Can be random or first morning specimen.

Midstream "Clean Catch"

  • For bacterial cultures or to prevent vaginal contamination.
  • Requires cleaning supplies, additional instructions to patient, and sterile container.
  • Requires thorough cleaning and rinsing of glans penis or urethral meatus before collection.
  • Begin urination into toilet, collect midstream portion in container, finish voiding in toilet.
  • This technique allows passage of the initial urine that may contain any urethral washings, such as normal flora bacteria, and allows collection of a specimen that represents elements and analytes from the bladder, ureters, and kidneys.

Catheterized Specimen

  • Requires collection by medical personnel.
  • Sterile catheter inserted through urethra into bladder.
  • Urine flows directly into collection bag.
  • Most often used for bacterial culture.
  • Specimen obtained anytime from collection bag.

Suprapubic Aspiration

  • Requires collection by medical personnel.
  • Involves puncturing of abdominal wall and distended bladder by using needle and syringe.
  • Sample aspirated directly from bladder.
  • Bladder urine normally is sterile.
  • Used principally for anaerobic cultures or in infants.

Pediatric Collections

  • Often commercially available plastic urine collection bags that attach with a hypoallergenic skin adhesive are used.
  • Patient’s perineal area cleaned prior to bag attachment.
  • Specimen removed as soon as possible after collection.
  • Specimen appropriate for routine testing.

Reasons for Specimen Rejection

  • Unlabeled or mislabeled specimen
    • Label should be on container, not on the lid
  • Mismatch of specimen name or identification (ID) number with order slip
  • Inappropriate collection technique for test ordered
  • Not properly preserved or time delay in receipt of specimen
  • Visibly contaminated sample
  • Insufficient volume for tests ordered

Containers and Labels

  • Clean, dry, and made of clear or translucent material, with lid to prevent spillage.
  • Need capacity of 50 to 100 mL.
  • Sterile containers required for cultures.
  • Extra-large commercial containers are available for large timed collections (24-hour specimens).
  • Usually made of a brown, opaque plastic to protect the specimen from light.
  • Label placed on container, not on lid.

Changes in Unpreserved Urine

  • Changes result from:
    • Alteration of urine solutes to a different form
    • Bacterial growth
    • Solute precipitation
  • Changes:
    • Decreased urine clarity and increased odor
    • Possible color changes from solute alteration
    • False-negative glucose
    • False-negative ketones
    • Increased nitrite and pH
    • Disintegration of formed elements

Handling and Preservation

  • Proper techniques to preserve integrity of specimen needed if delay is 2 hours or more.
  • Preservative considerations:
    • Type of collection
    • Tests to be performed
    • Time delay before testing
  • Refrigeration is the most common preservation technique, but should not be used for routine testing if urine will be analyzed within 2 hours.

Preservation of Timed Collections

  • 12- and 24-hour timed collections require the addition of a chemical preservative to maintain the integrity of the analyte to be tested.
  • Keep on ice or refrigerate during the collection period.
  • Check the collection manual to identify the necessary preservative.
  • Deliver specimen to the laboratory immediately after completion of the collection period.

Is This Fluid Urine?

  • Often needed in drug screen collections or specimens collected by needle aspiration.
  • Also helpful during traumas.
  • Urine creatinine concentrations 50 times higher than plasma.
  • Urea, sodium (Na), and chloride (Cl) higher in urine than in other body fluids.
  • Physiologic range is 1.002 to 1.035 for urine specific gravity and 4.0 to 8.0 for pH.
  • Urine from healthy persons contains no protein or glucose, whereas many other body fluids do.