Urine Composition and Analysis

Urine Composition

• Urine is around 95% water, with the remaining 5% composed of dissolved solutes.
• Solutes in urine provide insight into the body's internal balance.
• Urea, originating from protein and amino acid breakdown in the liver, constitutes about half of all dissolved substances.
• Creatinine, a byproduct of muscle metabolism, is an organic compound found in urine.
• Uric acid, from the breakdown of DNA/RNA purines, is present in urine.
• Chloride is the primary inorganic compound in urine, followed by sodium and potassium.
• Urine contains trace amounts of various other inorganic substances, influenced by diet, activity, metabolism, and hormones.
• Hormones, vitamins, and medications are present in urine, especially after being processed by the body.
• Cells (red or white blood cells), casts, crystals, mucus, and bacteria are considered formed elements that may be in urine.
• Elevated levels of formed elements in urine can indicate the presence of disease.
• Elevated white blood cells may suggest a urinary tract infection.
• Creatinine, urea, sodium, and chloride levels are much higher in urine than in other bodily fluids.
• Glucose or protein presence in urine can indicate diabetes or kidney disease.

Urine Volume

• Urine volume is determined by the amount of water kidneys excrete, reflecting hydration status.
• Fluid loss from sweating, vomiting, diarrhea, or burns affects urine output.
• Increased water intake leads to increased urine production.
• Antidiuretic hormone (ADH) prompts kidneys to reabsorb water, impacting urine volume.
• Less ADH results in increased urine output, while more ADH results in decreased urine production.
• Excess glucose or salts in the body lead to increased urine volume as they are excreted.
• Normal daily urine output is about 1200–1500 mL.
• A range of 600 to 2000 mL is still considered normal depending on various factors.
• Oliguria is defined as insufficient urine output, less than 400 mL/day in adults, indicating dehydration.
• Anuria signifies no urine output, possibly indicating kidney failure.
• Nocturia involves producing more urine at night, unlike the typical higher daytime output.
• Polyuria is excessive urine output, defined as more than 2.5 L/day in adults.
• Polyuria may arise from diabetes mellitus, diabetes insipidus, or substances blocking ADH.

Diabetes Mellitus vs. Diabetes Insipidus

• Diabetes mellitus and diabetes insipidus both result in polyuria and increased thirst, but for different reasons.
• Diabetes mellitus involves high blood glucose levels due to lack of insulin or insulin resistance.
• Excess glucose ends up in urine because the kidneys can't reabsorb it all, pulling water along and increasing urine volume.
• Urine in diabetes mellitus has high specific gravity due to glucose concentration.
• Diabetes insipidus is caused by a lack or dysfunction of ADH, impairing water reabsorption by the kidneys.
• Urine in diabetes insipidus is dilute with low specific gravity.
• Key difference: Diabetes mellitus has high glucose levels and high specific gravity, whereas diabetes insipidus involves low ADH and low specific gravity.

Specimen Collection

• Proper urine specimen collection significantly impacts the accuracy of urinalysis results.
• Standard Precautions (SP) should be followed, where gloves are always worn as urine is treated as a biohazard.
• Urine samples should be collected in clean, dry, and leakproof containers, preferably disposable.
• Specialized containers such as adhesive bags, large jugs, and screw-top lids are appropriate in certain situations.
• Routine urinalysis requires containers with a wide mouth, flat bottom, and clear material, holding about 50 mL.
• Sterile containers are required for microbiological testing, especially when testing is delayed.
• Transfer devices facilitate sterile urine transfer into tubes, enhancing safety and cleanliness.
• Specimens should be labeled immediately after collection and directly on the container (not the lid) with specific required information.
• Each sample must have a requisition form with matching information, including clinical details.
• The time the lab receives the specimen must be recorded.

Specimen Rejection

• Labs must reject specimens if integrity is compromised, resulting in untrustworthy findings.
• Common reasons for rejection include unlabeled or improperly labeled containers.
• Mismatches between the label and requisition form result in rejection.
• Contamination with feces or toilet paper can alter results, especially in microbiology testing.
• Contaminated container exteriors pose a safety risk and poor collection technique.
• Insufficient quantity leads to rejection since all tests required cannot be run.
• Improper transport and non-compliance with preservation after a delay can invalidate results.
• Nonsterile collection for urine culture will cause rejection due to potential for false results.
• The wrong type of collection for the test ordered requires rejection.
• Never discard a specimen without consulting a supervisor.
• Every lab should have written rejection policies to ensure consistency and fairness.

Specimen Handling

• Urine specimens undergo chemical and cellular changes soon after collection, affecting results if not handled correctly.
• Urine should be delivered to the lab and tested within 2 hours of collection.
• Refrigeration at 2°C to 8°C or adding a chemical preservative can preserve the sample if testing is delayed.
• Refrigeration slows bacterial growth and chemical changes for up to 24 hours.
• Samples must return to room temperature before testing, especially for reagent strip methods.
• Refrigeration can cause crystal formation, such as amorphous urates or phosphates.
• Chemical preservatives are used when refrigeration is not possible, particularly for long-distance transport.
• The ideal preservative is bactericidal, inhibits urease activity, preserves formed elements, and does not interfere with chemical tests.

Types of Urine Specimens

• A random specimen is the most common to be collected at any time for routine screening.
• Patient's recent food intake or exercise can affect results.
• First Morning Specimen is the ideal sample for screening due to being highly concentrated.
• The First Morning Specimen is also preferred for pregnancy tests and checking orthostatic proteinuria.
• 24-Hour Specimen is required for quantitative results to measure electrolytes, hormones, or catecholamines.
• Sample must be kept on ice or refrigerated the whole time.
• Catheterized Specimen involves collecting urine directly from the bladder using a catheter.
• It is commonly done when a sterile sample is needed for bacterial cultures.
• Midstream Clean-Catch Specimen involves voiding the first portion, then collecting the midstream part.
• It is the preferred method for urine cultures due to reduced contamination.
• Suprapubic Aspiration involves inserting a needle directly into the bladder to withdraw urine.
• This is used when a completely sterile sample is needed, and is also used for cytology studies.
• Three-Glass and Four-Glass Collections are used for diagnosing prostatic infections.

Three-Glass Collection Method

• First, clean the genital area.
• Collect the first portion of urine (urethral), midstream urine (bladder), and post-prostate massage urine (prostatic secretions)
• High WBC count in the third specimen and bacterial count 10x higher than the first indicates infection.
• Lipid-laden macrophages may be present.
• If the second sample already has bacteria, the third might just be contamination.

Pre- and Postmassage Test

• A midstream sample is collected.
• A prostate massage is done.
• Another sample is then collected.
• A 10-fold increase in bacteria in the post-massage sample points to prostatitis.

Stamey-Meares Four-Glass Test

• VB1: first 10 mL of urine (urethra)
• VB2: midstream urine (bladder)
• EPS: prostate fluid
• VB3: first 10 mL post-massage urine (residual prostate fluid)
• All sent to culture and microscopy, checking for WBCs, macrophages, bacteria, fungi, and even oval fat bodies.
• VB1 screens the urethra.
• VB2 screens the bladder.
• EPS & VB3 evaluate the prostate.
• A WBC count of 10–20/HPF in EPS is abnormal.

Pediatric Specimen Collection

• Routine Collection utilizes soft plastic bags with hypoallergenic adhesive.
• The genital area before applying the bag needs to be cleaned and dry.
• Avoid contamination from feces or surrounding skin areas.
• Once urine is collected, transfer and label it immediately.
• For Sterile Specimens, catheterization or suprapubic aspiration is used.
• Clean thoroughly with soap and sterile water.
• A sterile collection bag must be applied.
• Transfer to a sterile container without touching the inside.

Drug Specimen Collection

• Drug Specimen Collection is highly regulated, especially in legal or employment situations.
• Chain of Custody (COC) tracks the specimen from start to finish.
• Each person who handles the sample is officially recorded.
• A Witnessed collection is when someone observes the patient urinate when tampering is suspected.
• An Unwitnessed collection is when a patient collects urine privately, then hands it over immediately.
• Temperature must be taken within 4 minutes (acceptable: 32.5°C to 37.7°C).
• The color, pH, and specific gravity are assessed.
• A pH > 9 or specific gravity < 1.005 suggests dilution or adulteration, resulting in recollection.
• Once verified, the sample is labeled, sealed, and transported according to protocol.