Chapter 3 - Introduction to Urinalysis

History and Importance

• Urine analysis marked the beginning of laboratory medicine, dating back to cavemen drawings and Egyptian hieroglyphs.
  • Early diagnosis was limited to physical examination of color, turbidity, odor, volume, viscosity, and even sweetness (by noting that certain specimens attracted ants).
• Hippocrates wrote a book on “uroscopy”, and it was used in the Middle Ages to train physicians.
  • A chart of 20 different urine colors and their respective significance was developed.
• The first chemical testing was developed by Frederik Dekkers’ by boiling urine to test for albuminuria, or the presence of albumin proteins in urine.
• Untrained and unliscenced physicians called “pisse prophets” began offering prescriptions to the public, leading to the legislation of the first medical laws.
• Thomas Addis developed methods for quantifying microscopic urine sediment by the development of the microscope in the 17th century.
• Richard Bright introduced urinalysis as a routine examination for patients in 1827; however, the increasing number and complexity of tests made this impractical.
  • However, modern advancements in testing, as well as the availability and cheapness of clinical information obtained from urine, regained its popularity and role in routine examinations.
• The Clinical and Laboratory Standards Institute (CLSI) defines urinalysis as “the testing of urine with procedures commonly performed in an expeditious, reliable, accurate, safe, and cost-effective manner,” and supports its significance for diagnosing and screening diseases, monitoring its progression and checking medical effectiveness.

Urine Composition

• Urine is normally made up of 95% water and 5% organic and inorganic solutes, though variations may occur due to dietary intake, physical activity, body metabolism, endocrine functions, and even body position.

Urine Volume

• It is dependent on the amount of water the kidneys excrete, and it is influenced by fluid intake, fluid loss from non-renal sources, variations in the secretion of antidiuretic hormone, and the need to excrete increased amounts of dissolved solids, such as glucose or salts.
• Although the normal daily urine output is usually 1200 to 1500 mL, a range of 600 to 2000 mL is considered normal.
  • Oliguria, a decrease in urine output, occurs if the body enters a state of dehydration as a result of excessive water loss from vomiting, diarrhea, perspiration or severe burns.
  • Anuria, the complete cessation of urination, occurs if there is serious damage or a decrease in blood flow to the kidneys.
  • Nocturia is an increase in urination frequency during the night.
  • Polyuria is an increase in daily urine volume often associated with diabetes mellitus and diabetes insipidus.
  • However, it can be artificially induced by diuretics, caffeine, alcohol or other substances that suppress ADH secretion.
  • Diabetes mellitus is caused by the inability to produce insulin, leading to increased glucose levels in blood that need to be excreted out. To compensate, more water is drawn out by the kidneys from the blood.
    • Urine samples appear dilute but have a high specific gravity.
    • A positive blood glucose test result confims it.
  • Diabetes insipidus is caused by the inability to produce ADH, preventing water to be removed by the tubules back to the bloodstream.
    • Urine samples are dilute with a low specific gravity.
  • An sign of polyuria is increased 24-hour urine specimen volume (see 24-Hour/Timed Specimen in Types of Specimens) with a pale yellow color (see Color in Chapter 4 - Physical Examination).

Specimen Collection

• Specimens must be collected in clean, dry, leak-proof containers.
  • Disposable containers are recommended because they eliminate the chance of contamination due to improper washing.
  • Properly applied crew-top lids are less likely to leak than snap-on lids.
  • They should have a wide mouth to facilitate collections from female patients and a wide, flat bottom to prevent overturning.
  • They should be made of a clear material to allow for determination of color and clarity.
  • The recommended capacity of the container is 50 mL, which allows 12 mL of specimen needed for microscopic analysis, additional specimen for repeat analysis, and enough room for the specimen to be mixed by swirling the container.
  • A 12-mL volume is frequently used because multiparameter reagent strips are easily immersed in this volume, and capped centrifuge tubes are often calibrated to this volume (see Specimen Preparation in Preparation and Examination of the Urine Sediment in Chapter 6 - Microscopic Examination of Urine).
    • If obtaining a 12-mL specimen is not possible, as with pediatric patients, the volume of the specimen used should be noted on the report form and is corrected afterwards with multiplication.
    • For example, if 6 mL of urine is centrifuged, the results are multiplied by 2.
  • For 24-hour specimens, larger containers are needed.
  • For microbiologic urine studies and for collection with more than 2 hours elapsed between analysis, individually packaged sterile containers with secure closures should be used.
  • All specimens must be labeled properly with the patient’s name and identification number, the date and time of collection, and additional information such as the patient’s age and location and the physician’s name, as required by institutional protocol.
  • Labels must be attached to the container, not to the lid, and should not become detached if the container is refrigerated or frozen.
  • A requisition form (manual or computerized) containing matching information as the label must accompany specimens delivered to the laboratory.
  • Additional information on the form can include method of collection or type of specimen, possible interfering medications, and the patient’s clinical information.
  • The time the specimen is received in the laboratory should be recorded on the form.
  • Specimens in unlabeled containers, non-matching labels and requisition forms, specimens contaminated with feces or toilet paper, containers with contaminated exteriors, specimens of insufficient quantity, and specimens that have been improperly transported should be returned and recollected.

Specimen Handling

• Specimens should be delivered to the laboratory promptly and tested within 2 hours; if not, they must be refrigerated at 2-8°C or have a chemical preservative.
  • If refrigerated, the specimen must return to room temperature (around 37°C) before testing to correct the specific gravity and dissolve precipitated amorphous sulfates and urates, especially before microscopic examination (see Specimen Preparation in Preparation and Examination of the Urine Sediment in Chapter 6 - Microscopic Examination of Urine).
  • Uroerythrin, a pink pigment, is most evident in specimens that have been refrigerated (see Color in Chapter 4 - Physical Examination of Urine).
  • Refrigerated specimens frequently develop a thick turbidity caused by the precipitation of amorphous phosphates, carbonates, and urates (see Clarity in Chapter 4 - Physical Examination of Urine).
  • The ideal preservative should be bactericidal, inhibit urease, preserve formed elements in the sediment, and not interfere with chemical tests.
  • However, an ideal preservative does not exist; therefore, a preservative that best suits the needs of the required analysis should be chosen.

• If it is to be cultured, it should be refrigerated during transit and held refrigerated until cultured up to 24 hours (see Types of Specimens below).
  • Such specimens include catheterized, midstream clean-catch, suprapubic aspiration and prostatitis/three-glass collection.

Types of Specimens

Random Specimen

• It is collected at any time.
• Some characteristics include a colorless or a pale yellow color, a pH ranging from 4.5 to 8.0 and a specific gravity ranging between 1.015 and 1.025 (see Color and Specific Gravity in Chapter 4 - Physical Examination of Urine; and pH in Chapter 5 - Chemical Examination of Urine).
  • Any random specimen with a specific gravity of 1.023 or higher is generally considered normal.
• It may also show erroneous results resulting from dietary intake or physical activity, so additional specimens may be collected under controlled conditions.

First Morning/8-Hour Specimen

• It is the ideal screening specimen.
• It is used for verifying false-negative pregnancy tests and evaluating orthostatic proteinuria, a condition where an abnormally large amount of protein is present in the urine while staying in an upright position.
• Some characteristics include a dark-yellow color and a slightly acidic pH of 5.0 to 6.0.
  • It is more concentrated so detection of chemicals and formed elements is easier.
  • It prevents interference of pH from alkaline tides after meals (see pH in Chapter 5 - Chemical Examination of Urine).
• The patient is instructed to collect urine immediately after and deliver it within 2 hours.

Second Morning/Fasting Specimen

• The patient undergoes a period of fasting before collecting urine to prevent interference of food metabolites and physiological changes, as it is used to monitor glucose levels for diabetes.

2-Hour Postprandial Specimen

• The patient is instructed to fast before being given a routine meal, after which he/she/they must collect a specimen 2 hours after eating.
• The specimen is tested for glucose and compared with a fasting specimen and blood glucose tests to monitor insulin therapy in persons with diabetes mellitus.

Glucose Tolerance Specimens

• The number of specimens correspond to the length of time and blood samples collected in a glucose tolerance test (GTT).
  • It may include fasting, half-hour, 1-hour, 2-hour, and 3-hour specimens, and possibly 4-hour, 5-hour, and 6-hour specimens.
• Specimens are tested for glucose and ketones to evaluate the patient’s ability to metabolize a measured amount of glucose and the renal threshold for glucose.

24-Hour/Timed Specimen

• When the concentration of the substance to be measured changes with diurnal variations and with daily activities such as exercise, meals, and body metabolism, 24-hour collection is required.
  • Many solutes exhibit diurnal variations such as catecholamines, 17-hydroxysteroids, and electrolytes in which the lowest concentration is in the early morning and the highest concentration occurs in the afternoon.
• The patient must start and end with an empty bladder, with all urine from the 24-hour period collected. On its arrival in the laboratory, a 24-hour specimen must be thoroughly mixed and the volume accurately measured and recorded.
• If volume is increased, it may be a sign of polyuria or diabetes insipidus (see Urine Volume).

Catheterized Specimen

• This specimen is collected under sterile conditions by passing a hollow tube (catheter) through the urethra into the bladder, or less frequently, through the ureters of the left and right kidneys.
  • It provides a specimen that is less contaminated by epithelial cells and bacteria
• This is usually done for bacterial tests.
  • It should be refrigerated during transit and storage, and it can be kept up to 24 hours (see Specimen Handling above).

Midstream Clean-Catch Specimen

• This is a safer, less traumatic method than the catheterized specimen for obtaining urine for bacterial culture and for microscopic examination.
• The urine clarity is usually clear.
• Patients must be provided with appropriate cleansing materials, a sterile container, and instructions for cleansing and voiding.
  • Strong bacterial agents, such as hexachlorophene or povidone-iodine, should not be used as cleansing agents.
  • Mild antiseptic towelettes are recommended.
• Patients are instructed to wash their hands and genitals before beginning the collection.
  • Male patients should clean the glans, the gland-like body at the tip of the penis which begins at the urethra, and withdraw the foreskin, if necessary.
  • Female patients should separate the labia and clean the urinary meatus, the external urinary opening, and surrounding area.
  • When cleansing is complete, patients are to void first into the toilet, then collect an adequate amount of urine in the sterile container, and finish voiding into the toilet. Care should be taken not to contaminate the specimen container.
• It should be refrigerated during transit and storage, and it can be kept up to 24 hours (see Specimen Handling above).

Suprapubic Aspiration

• Occasionally, urine may be collected by external introduction of a needle through the abdomen into the bladder.
  • It provides a sample for bacterial culture that is completely free of extraneous contamination.
  • The specimen can also be used for cytologic examination.
  • It should be refrigerated during transit and storage, and it can be kept up to 24 hours (see Specimen Handling above).

Prostatitis/Three-Glass Collection Specimen

• The first collection is the first urine passed in the day. The second collection is a midstream specimen. Lastly, the prostate is massaged so that prostate fluid will be passed with the remaining urine.
• Quantitative cultures are performed on all specimens, and the first and third specimens are examined microscopically.
  • It is expected in cases of prostatic infection that the third specimen will have a white blood cell/high-power field count and a bacterial count 10 times that of the first specimen. Macrophages containing lipids may also be present.
  • The second specimen is used as a control, and if positive, the results from the third specimen are invalid because infected urine has contaminated the specimen.
• Variations of the procedure include the Stamey-Mears four-glass localization method and the preand postmassage test (PPMT).
  • The four-glass method consists the same specimens as the three-glass method with an additional specimen for expressed prostatic secretions (EPS).
  • The first specimen is tested for urethral infection or inflammation, and the second specimen is tested for urinary bladder infection. The prostatic secretions are cultured and examined for white bood cells, with more than 10 to 20 white blood cells per high-power field indicating abnormality.
  • In the PPMT test, a clean-catch midstream urine specimen is collected.
  • A positive result is significant bacteriuria in the postmassage specimen of greater than 10 times the premassage count.
• It should be refrigerated during transit and storage, and it can be kept up to 24 hours (see Specimen Handling above).

Pediatric Specimen

• Soft, clear plastic bags with hypoallergenic skin adhesives to attach to the genital area of both boys and girls are used.
  • For quantitative testing, bags are available that allow a tube to be attached and excess urine transferred to a larger container.

Drug Specimen Collection

• The chain of custody (COC) is a standardized form that must document and accompany every step of drug testing, from collector to courier to laboratory to medical review officer to employer.

  • For urine specimens to withstand legal scrutiny, it is necessary to prove that no tampering of the specimen occurred, such as substitution, adulteration, or dilution.

• The urine drug specimen collection procedure is as follows:

  1. The collector adds bluing agents/dyes to the toilet water reservoir and tapes the toilet lids and faucet handles to prevent adulteration of samples as much as possible.
  2. The donor provides identification, after which the collector completes step 1 of the chain of custody (COC) form and has the donor sign the form.
     • Identification can be through photo identification or with an employer representative with a photo ID is required.
  3. The donor leaves his or her coat, briefcase, and/or purse outside the collection area to avoid the possibility of concealed substances contaminating the urine.
  4. The donor washes his or her hands and receives a specimen cup.
  5. The collector remains in the restroom but outside the stall, listening for unauthorized water use, unless a witnessed collection is requested.
     • The decision to obtain a witnessed collection is indicated when it is suspected that the donor may alter or substitute the specimen or it is the policy of the client ordering the test.
     • If a witnessed specimen collection is ordered, a same-gender collector will observe the collection of urine.
  6. The donor hands specimen cup to the collector and the transfer is documented.
  7. The collector checks the urine for abnormal color and for the required amount (30–45 mL).
  8. The collector checks that the temperature strip on the specimen cup reads 32.5–37.7°C within 4 minutes from the time of collection. The collector records the in-range temperature on the COC form (COC step 2). If the specimen temperature is out of range or the specimen is suspected to have been diluted or adulterated, a new specimen must be collected and a supervisor must be notified.
  9. The specimen must remain in the sight of the donor and collector at all times as the collector peels off the specimen identification strips from the COC form (COC step 3) and puts them on the capped bottle, covering both sides of the cap.
  10. The donor’s intials, date and time are written on the seals.
  11. The donor and the collector completes step 4 and step 5 on the COC form, respectively.
  12. Each time the specimen is handled, transferred, or placed in storage, every individual must be identified and the date and purpose of the change recorded.
  13. The collector follows laboratory-specific instructions for packaging the specimen bottles and laboratory copies of the COC form.
  14. The collector distributes the COC copies to appropriate personnel.