Urine Sample Collection and Analysis
Prepared by:
Dr. Salma Elgazzar
Learning Objectives
- Recognize the value of urine analysis as a screening tool for renal and non-renal diseases.
- Identify types of urine specimens and methods of collection.
- Differentiate between macroscopic and microscopic urine examinations.
- Identify reference values for a normal urine analysis.
- Interpret the meaning of abnormal values in a urine analysis.
- Recognize nursing diagnoses and propose interventions for patients with abnormal urine test findings.
Indication of Urine Analysis
A urine analysis (UA) is a simple, non-invasive diagnostic tool that examines the visual, chemical, and microscopic properties of urine. It can be used to diagnose and monitor various medical conditions, including:
- Kidney disorders and function
- Urinary tract infections
- Systemic diseases such as diabetes mellitus
- Inborn errors of metabolism
- Toxicology screening
Types of Urine Specimens & Methods of Collection
The most common error in managing UTI in children is the failure to establish the diagnosis properly. The method of collection depends on the patient’s age.
For Children in Nappies:
-
Clean-Catch Sample: Recommended method. Collect urine into a clean pot when the nappy is removed. Encourage urination by gently rubbing the lower abdomen with gauze soaked in cold water (Quick-wee technique).
-
Adhesive Plastic Bag: Applied to the perineum after careful washing. May be contaminated by skin or feces (not suitable for urine culture).
-
Urethral Catheter: Used if there is urgency in obtaining a sample and no urine has been passed.
-
Suprapubic Aspiration: A fine needle attached to a syringe is inserted directly into the bladder under ultrasound guidance; used in severely ill infants.
For Older Children:
- Midstream Sample: Requires careful cleaning and collection to avoid contamination from under the foreskin in boys and reflux of urine into the vagina during voiding in girls.
First half of stream serves to flush out contaminating cells and microbes from urethra and perineum.
Early morning sample is preferred for microscopic examination & sediment because of highest concentrations of cells, not affected by exercise.
Clean Catch Urine Collection
Adhesive Bag Urine Collection
Suprapubic Urine Collection
Midstream Clean Catch
- Early morning sample is preferred for microscopic examination of sediment as it contains the highest concentration of cells and is not affected by exercise.
- Collected urine should be evaluated quickly, no later than 2 hours after collection.
- Proper cleaning of genitalia is especially important in girls.
Precautions For Urine Analysis
- 1.Urine can be refrigerated for 6 to 8 hours.
- 1.At low temperatures, there will be precipitation of amorphous urates or phosphates.
- 2.Bring the refrigerated urine to room temperature before testing.
- 3.Urine collected for more than 2 hours may be rejected.
- 4.The decomposition of urine begins in 30 minutes at room temperature and 4 hours in refrigeration.
- 5.For longer periods, boric acid can be used as a preservative.
Macroscopic Urinalysis
- Uses a urine dipstick to assess urine concentration, pH, and the presence of blood, protein, glucose, ketones, and leukocytes (via leukocyte esterase reaction).
- Sensitive to the presence of hemoglobin (or myoglobin); few false-negative results but many false-positive results.
- The nitrite test may detect bacteriuria if bacteria can reduce nitrate to nitrite and have sufficient urine contact time.
Microscopic Urinalysis
- Confirms pyuria and hematuria and detects casts and crystals.
- Proteinuria can be more accurately assessed by a spot urine Protein/Creatinine (upr/cr) ratio in a single urine specimen, preferably from a first-morning void. This value correlates well with 24-hour urine protein excretion.
Urine Analysis Components
Urine Normal Values Summary
| Urine Substances | Normal Values | Collection Timings | Significance |
|---|---|---|---|
| Color | Pale-yellow to dark amber | A random sample | Red color urine: Check for hemoglobin |
| OdorY | Faint aromatic | A random sample | Diabetic urine has a fruity (acetone) odor. |
| Volume | 800 to 2000 mL | A random sample, 24-hour urine sample | Polyuria: Increased urine output. with normal bun and creatiinine Oliguria: <500 mL |
| Blood | Negative | A random sample | Seen in various urinary tract conditions |
Various Colors of Urine
- Colorless or Pale Yellow: Normal
- Dark Yellow: Concentrated
- Green: Pseudomonas infection
- Yellow-Green: Bilirubin oxidized to Biliverdin
- Brown-Black: RBCs, Methemoglobin, Alkaptoneuria
Urine Turbidity
Pathological Causes
- White blood cells
- Red blood cells
- Presence of bacteria
- Presence of yeast
- Abnormal crystals
- Lymph fluids and lipids
Physiological Causes
- Mucus
- Squamous epithelial cells
- Presence of spermatozoa
- Crystaluria
- Contrast media
- Fecal contamination
Various Causes of Urine OdorY
| Odor Type | Etiology |
|---|---|
| Aromatic | Normal |
| Fruity, Sweet | Ketone (in diabetes mellitus), Starvation, Vomiting |
| Mousy (Musty Odor) | Phenylketonuria |
| Foul, Ammonia-like | Bacterial contamination, Urinary tract infection |
| Maple Syrup | Maple syrup urine disease |
| Fetid Odor | Infection, possibly due to E.Coli |
Chemical Analysis
The presence of normal and abnormal chemical elements in urine is detected using dry reagent strips.
The chemical reaction results in a specific color range.
It is a semiquantitative method that depends on the degree of color appearance, providing an estimation of the substance amount rather than an accurate measurement.
Urine Substances to be Checked
| Substance | Normal Values | Collection Timings | Significance |
|---|---|---|---|
| pH | 4.7 to 7.7, Average = acidic 6.0 | A random and fresh sample | Urine pH never reaches 9. - incase of 9, test the fresh sample Acidic urine: High protein diet, Metabolic and respiratory acidosis. Alkaline urine: Vegetarians, Metabolic and respiratory alkalosis, Bacteria splitting urea to ammonia. |
| Specific Gravity | 1.008 to 1.030, Average = 1.018 | A random sample, 24-hour urine sample | Specific gravity is the measurement of the kidneys’ ability to concentrate urine. Low: Tubular disordres Polyuria High: dehydration |
| Protein | Qualitative = nil, Quantitative = 0 to 0.1 g/24 hours | 24-hour urine sample | Indicates renal disease, may be transient. |
Glucosuria and Ketonuria
- Glucosuria Causes: Diabetes mellitus (with high blood glucose level), Proximal tubular disorders (normal serum blood glucose level).
- Ketonuria Causes: DKA, Starvation states (prolonged fasting, anorexia nervosa).
Normally glucose and ketones is not present in urine
Dipsticks detect mainly albuminuria and are less sensitive for other forms of proteins.
It offers only a rough qualitative and semi-quantitative measurement of urinary protein excretion, so it should be confirmed by additional testing.
Positive Dipstick for Blood
A positive dipstick for blood may indicate:
- Hematuria
- Hemoglobinuria (intravascular hemolysis)
- Myoglobinuria (muscle injury or disease)
A positive dipstick test for blood should be followed by microscopic examination to detect RBCs.
Leukocyte Esterase & Nitrite
Confirmation of UTI, when both are positive, treat with antibiotics
Microscopic Examination
We will examine for:
- Cells
- Casts
- Crystals
- Microorganisms
Cells in Urine
- RBCs: Number & dysmorphic RBCs - Hematuri
- WBCs: Number, may indicate inflammation or infection - UTI
- Epithelial Cells: May appear in urine after being shed from anywhere within the genitourinary tract, present in urine in few numbers.
Casts in Urine
- Cylindrical structures formed in the renal tubules.
- Formed only in distal convoluted tubules and collecting ducts.
Routine Urine Analysis Example
| Parameter | Result |
|---|---|
| Quantity | Adequate |
| Color | Yellowish |
| Appearance | Clear |
| Specific Gravity | 1.030 |
| Reaction | Acidic |
| Albumin | Nil |
| Sugar | Nil |
| Microscopic Exam | |
| Pus Cells | 2-3 (HPP) |
| RBC Cells | Nil (HPP) |
| Epithelial Cells | 1-2 (LP) |
| Casts | Nil |
| Crystals | Nil |
| Bacteria | Nil |
| Others | Nil |