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Urine Analysis:- Physical Examination, and Interpretation (Part 3)

May 10, 2022Lab TestsUrine Analysis

Urine Analysis, Physical Examination

Urine Analysis

  • These are the normal constituents and findings in the normal urine.
  • Routine urinalysis includes:
    1. Physical character.
    2. Chemical analysis.
    3. Microscopic examination.

Precautions for urine collection

  1. Urine must be analyzed within one hour of collection if held at room temperature.
  2. Keep urine at 2 to 8°C if delayed >8 hours.
  3. If urine is kept for a longer time, then it will get a false positive test like nitrite will be positive.
  4. Urea-producing organisms will degrade urea to ammonia and change the pH to alkaline.
  5. Change in pH causes degeneration of cast and cell lysis.

Factors that will interfere with the urine analysis:

  1. There are certain foods that will color the urine like:
    1. Carrots will change their urine color to dark yellow.
    2. Beets may cause red color urine.
    3. Rhubarb will change its color to red or brown.
  2. Asparagus produces a typical urine odor.
  3. If you keep urine on the table, bacteria will change the urine pH, make it alkaline because of urea splitting bacteria and there is the production of the ammonia.
  4. Effect of the food on the urine pH:
    1. Eating citrus fruits, dairy products, and vegetables makes urine alkaline.
    2. A high protein diet and some foods (cranberries) make urine acidic.
    3. A high protein, a fat diet without the intake of carbohydrates also causes ketonuria.
  5. When radiopaque contrast media is given to the patient will give false-positive urine protein for at least 3 days.
  6. Females may have contamination from the vaginal secretions and show an increased number of WBCs.
  7. Traumatic catheterization may cause hematuria and false RBCs in the urine.
  8. Vaginal secretions contamination may cause false-positive leucocyte esterase.
  9. False proteinuria is seen when urine is contaminated with vaginal secretions.
  10. Urine culture gives false-positive results when contaminated with stool, vaginal secretions, and contaminated test tubes or hands and clothes.

Urine Physical examination:

Color

  1. The color of the urine varies from colorless to black.
  2. This variation in the color depends upon:
    1. Metabolic functions.
    2. Physical activity.
    3. Ingested food.
    4. Pathologic conditions.
  3. Any change in the color needs to work up to find the cause.
  4. The yellow color of the urine is due to pigment, which is called urochrome and is produced as endogenous metabolism.
  5. Color intensity depends upon the concentration of the urine.
  6. Concentrated urine is darker in color.
  7. The pale yellow to light color is due to diluted urine.
  8. The Yellow to amber color is due to urochromes, which are derivatives of urobilin, the end product of bilirubin degradation.
  9. Yellowish-brown to green color is due to bile pigments oxidation.
    1. While the blue/green color is due to pseudomonas infection.
  10. Blue urine color is due to the intake medication of methocarbamol, methylene blue, and amitryptiline.
  11. Red and brown after standing are due to porphyrins.
  12. The reddish-brown color in the fresh sample is from hemoglobin and red blood cells.
    1. When RBCs are there for several hours in acidic urine, it will give rise to brown color due to oxidation of the methemoglobin.
    2. Hemoglobinuria shows red plasma due to hemolysis of the RBCs.
    3. Myoglobin is cleared from the plasma rapidly so that the plasma will be clear.
Urine physical examination, Urine positive for blood by chemical test

Urine physical examination, Urine positive for blood by chemical test

  1. Urine positive for blood by chemical tests, the brownish-black color ion is standing in the urine due to alkaptonuria because of the homogentisic acid excretion. In this case, the chemical blood tests will be negative.
  2. In the case of malignant melanoma where melanogen oxidizes in the air to melanin.
  3. Drugs and some foods like beets may change the urine color.
  4. If urine shows large foam on shaking, it indicates an increased amount of protein in the urine.

Urine color variations:

Urine color Etiology for the color
Pale yellow to light
  • Normal color
Orange
  • Concentrated urine
Pale yellow
  • Polyuria, Diabetes inspidus, and Mellitus
Deep yellow
  • Riboflavin
Dark  yellow and dark color
  1. Concentrated urine
  2. Bilirubin
  3. Urobilin
  4. Biliverdin
Yellow to amber
  1. Urobilin
  2. Bilirubin
  3. Biliverdin
Amber orange
  1. Bilirubin
  2. Nitrofurantoin
  3. Pyridium
Yellow-brown or yellow-green
  • Bilirubin oxidized to biliverdin.
Yellowish-brown to green
  1. Bile pigments
  2. Bacteria (pseudomonas)
Red and brown after keeping the urine
  • Porphyrins
Redish brown in fresh urine
  1. Hemoglobin and red blood cells
  2. Myoglobin
  3. Porphobilinogen
  4. Porphyrins
Pink to red
  1. RBCs
  2. Hemoglobin
  3. Myoglobin
  4. Beets,
  5. Rifampicin
  6. Menstrual contamination
Brownish-black color
  • Alkaptonuria
Changing color
  • Some of the drugs
Green
  1. Pseudomonas infection
  2. Biliverdin
Green-yellow
  • Flavones in some vitamins
Green or blue
  • Methylene blue
Brown-black
  1. RBCs oxidized to methemoglobin.
  2. Melanin
  3. Homogentisic acid
  4. Metronidazole
  5. Methyldopa

Drugs that can change the color of the urine:

Drugs Effect of the drug on the body Change in the urine color
Chloroquine Antimalarial drug Rusty yellow or brown
Iron preparation Treat the anemia Drak brown and becomes black on standing
Nitrofurantoin Antibacterial for UTI Brown
Pyridium (Phenazopyridine) Urinary tract analgesic orange to red
Dilantin Anticonvulsant for epilepsy Pink, red, or red-brown
Vitamin B 2 (Riboflavin) Vitamin supplement Dark yellow
Levodopa Treat Parkinson’s disease Dark-brown on standing
Rifampicin Antibacterial for TB Red-orange
Dyrenium ( Triamterene) Diuretic Pale-blue
Cascara sagrada Laxative Red in alkaline urine and yellow-brown in acidic urine
Doxidan (Docusate calcium) Laxative Pink to red to red-brown
Phenolphthalein Laxative Red or purplish-pink in alkaline urine
Phenothiazine Antiemetic, antipsychotic, neuroleptic Red-brown
Sulfasalazine Antibacterial Orange-yellow in alkaline urine

Urine color changes due to pathological and nonpathological conditions:

Urine color Pathological causes Nonpathological causes
Red or reddish-brown
  1. Hemoglobin
  2. RBC
  3. Myoglobin
  4. Porphyrins
  1. Drugs
  2. Dye
  3. Beets
  4. Rhubarb
  5. Senna
Green
  1. Biliverdin
  2. Bacteria (pseudomonas)
  1. Vitamins
  2. Diuretics
  3. Psychoactive drugs
Blue or blue-green
  • None
  1. Urinary germicide
  2. Diuretics
Orange
  • Bile pigments
  1. Drugs like pyridium
  2. Phenothiazine
Yellow-orange or yellow-brown
  1. Bilirubin
  2. Urobilin
  3. Dehydration
  4. Fever
  1. Carrots
  2. Riboflavin
  3. Nitrofurantoin
Black or brownish-black
  1. Urobilin
  2. Melanin
  3. Methemoglobin
  1. Iron preparations
  2. Levodopa
Milky or opalescent
  1. Bacteria and not cleared by acid
  2. Fat globules (lipiduria)

Various colors of the urine:

Urine physical examination, Various colors of the urine

Urine physical examination, Various colors of the urine

Odor

  1. This is not part of the urine analysis. It has no clinical significance.
  2. Odor has little value in the diagnosis of various possibilities.
  3. There is a typical ammonia smell.
    1. When urine is sometimes kept on the table, the odor of ammonia (NH 3) becomes more prominent.
    2. The breakdown of the urea by the bacteria in the urine is responsible for the ammonia smell.
  4. The characteristic pungent odor in fresh urine is due to volatile aromatic acids.
  5. Urinary tract infection gives a noxious, fecal smell, and it is unpleasant to smell.
  6. Diabetic urine often smells fruity as a result of ketones.
  7. Ingestion of onions, garlic, and asparagus can cause an unusual or pungent odor.
  8. Maple syrup odor is seen in maple syrup disease.
  9. A bleach-like smell is seen in the contamination.
  10. The mousy odor is seen in phenylketonuria.

Various odors of the urine:

Odor The reason for that odor
Faint aromatic (fresh urine) Due to ammonia
Strong, unpleasant odor Bacterial infection
Sweety or fruity odor Diabetes mellitus ketone bodies
Maple syrup odor Maple syrup disease
Unusual pungent odor Ingestion of onions, garlic, and asparagus
Mousy odor Phenylketonuria
Sweet smell Malnutrition, vomiting, and diarrhea

Clarity

  1. Normal urine is clear and is judged against the light source.
  2. The cloudiness of the urine specimen depends on pH and dissolved solids components like amorphous phosphates and carbonates.

Urine clarity variables:

Urine degree of clarity (cloudiness)
Criteria
Clear
  • No visible particulate material is seen.
Hazy
  1. Can see visible particulate material
  2. Can read the newspaper
Cloudy
  1. Can see the newspaper
  2. But the words are distorted or not clear.
Turbid
  1. Can not see the newspaper through the urine tube

Turbidity:

  1. It is generally due to gross bacteriuria.
  2. In alkaline urine, turbidity is due to amorphous phosphates and carbonates.
  3. In acidic urine, turbidity is due to amorphous urates.
  4. Smoky urine is due to hematuria.
  5. In women, the epithelial cells and mucus may result in hazy urine.
  6. Urine, when kept in the fridge, may become turbid without any pathology.
    1. In the refrigerated urine, amorphous phosphates, carbonates, and urates give rise to thick turbidity.
  7. Other turbidity causes are contamination with semen, feces, vaginal cream, talcum powder, and contrast media.
  8. Turbidity may be seen in bacterial infection and the presence of RBCs and WBCs.

Common causes of cloudiness in the urine:

Normal causes Pathologic causes
Amorphous phosphate Amorphous urates
Amorphous urates Abnormal crystalluria like cysteine, tyrosine
Presence of normal crystals RBCs, WBCs, fat cast
Mucus Epithelial cells like renal transitional cells
Bacteria Bacteria in fresh urine
Spermatozoa Yeast, fungi, and parasites
Prostatic fluids Fecal material
Epithelial cells (squamous cells) Chyluria due to lymph is, although rare
Contamination by powder, antiseptic positive for malignant cells

Various causes of turbidity:

The Effects of chemicals used on urine Possible cause of the turbidity
Acidic urine Amorphous urates, uric acid, contrast media
Alkaline  urine Amorphous phosphates, carbonates
Solubility on heating the urine Uric acid crystals and amorphous urates
Insoluble in dilute acetic acid Bacteria, yeast, WBCs, spermatozoa
Solubility in dilute acetic acid Amorphous phosphate, carbonates, and RBCs
Solubility in ether Lipids, lymph fluid

Specific gravity

  1. The kidneys’ ability to selectively absorb essential chemicals (electrolytes) and water from the glomerular filtrate is one of the most important body functions.
  2. Specific gravity <1.003 is mostly not the urine.

Definition of specific gravity:

  1. This is the weight of 1 mL of urine in grams divided by 1 mL of water.
Urine specific gravity formula

Urine specific gravity formula

  1. This helps to give the state of hydration and dehydration.
  2. This indicates the concentrating ability of the kidney.
  3. The specific gravity of the urine can be measured by:
  4. Urinometer (hydrometer):
    1. This consists of a weighted float attached to the scale that has been calibrated to urine-specific gravity.
Urine Urinometer

Urine Urinometer

  1. Refractometer:
    1.  This will determine the concentration of the dissolved particles in the urine. This will do by measuring the refractive index. This refractive index compares the velocity of the light in air with the velocity of light in the solution.
        1. The refractometer’s advantages are that it needs two or three drops of urine.
Urine Refractometer

Urine Refractometer

  1. Chemical reagents strips:
    1.  These are disposable colorimetric reagent strips. No instrument is needed.
  2. Automated instruments.

Normal urine specific gravity :

  • 1.003 to 1.030 (1.005 to 1.030).
  1. Most urine fall in the range of 1.015 to 1.025.
  2. Newborn = 1.012
  3. Infants = 1.002 to 1.006
  4. Adult = 1.002 to 1.030
  • After 12 hours of fluid restriction = >1.025
  • Urine 24 hours = 1.015 to 1.025
  • The diluted urine range is 1.000 to 1.010.
  • Concentrated urine is 1.025 to 1.030.

Low specific gravity urine (hyposthenuria) is seen in:

  1. Diabetes inspidus (not go above 1.001 to 1.003. ADH hormone is lacking.
  2. Pyelonephritis.
  3. Glomerulonephritis.
  4. The consistent low specific gravity of 1.010 is known as isosthenuria. It is seen in chronic renal disease, where the capacity of concentrating urine is lost.

High specific gravity urine (hypersthenuria) is seen in:

  1. Diabetes mellitus.
  2. Congestive heart failure.
  3. Dehydration due to sweating, fever, and vomiting or diarrhea.
  4. Adrenal insufficiency.
  5. Liver disease.Nephrosis.

pH

  1. The lungs and the kidneys are major regulators of the acid-base balance of the body.
  2. These two organs control the pH by the secretion of hydrogen ions in the form of ammonium ions, hydrogen phosphate, and weak organic acids.
  3. These organs can maintain the pH by reabsorption of HCO3–, from the filtrate in the convoluted tubules.
Urine pH control by the lungs and kidneys

Urine pH control by the lungs and kidneys

  1. Urine pH must be performed on a fresh urine sample because the urine tends to change the pH on standing.
  2. The first-morning sample shows a pH of 5 to 6.
    1. After the meal pH may be alkaline pH.
    2. Urine pH is 4.6 to 7.0 and the average is 6.0
  3. pH depends upon the diet.
  4. pH <7.0 is primarily caused by the phosphates, which are excreted as salts conjugated to Na+, K+, Ca+, and NH4+.
    1. Acidity also reflects the excretion of nonvolatile metabolic acids pyruvate, lactate, and citrate.
  5. The acidity of urine is seen in:
    1. Systemic acidosis in diabetes mellitus.
    2. Renal tubular acidosis.
  6. The alkaline urine (>7.0) is seen in:
    1. This is a normal reaction to the gastric acidity  (HCL) dumped into the duodenum and then to circulation.
    2. Urinary tract infection.
    3. Bacterial contamination of the urine.
    4. Medications like sodium citrate and sodium bicarbonate will reduce pH.
    5. Fanconi’s syndrome is congenital generalized aminoaciduria due to defective proximal tubular dysfunction.

Causes of acidic and alkaline urine:

Alkaline urine (pH is alkaline) Acidic urine (pH is acidic)
  1. Due to vomiting
  2. Vegetable diets
  3. Low carbohydrate diet
  4. Chronic renal failure
  5. Renal tubular acidosisis
  6. Bacteria (ammonia producing and urea splitting bacteria)
  7. Respiratory and metabolic alkalosis
  8. Acetazolamide therapyy
  1. Starvation
  2. Dehydration
  3. Diarrhea
  4. Protein diet
  5. Metabolism of fats
  6. Respiratory and metabolic acidosis
  7. Sleep
  8. Acid-producing bacteria
  9. Diabetic acidosis

Osmolality (Osmolarity)

  1. Definition:
    1. Specific gravity depends on the number of particles present in a solution and the particles’ density, whereas osmolarity is affected only by the number of particles present.
    2. Osmolarity is the number of solute particles in one liter of the solvent.
    3. Osmolality is the number of solute particles in one Kg of solvent.
    4. The unit of the osmolarity is Osm/L.
  2. The difference in the dilute solution is negligible.
    1. Osmolality is preferred over osmolarity because it is higher.
    2. When evaluating the ability of kidneys concentration, Na+, K+, and Urea are important. All these three contribute to the osmolarity of the urine.
    3. Example: Osmolal solution of the Glucose is 180 g dissolved in 1 Kg of solvent.
      1. The osmolar solution of glucose is 180 g dissolved in 1 Liter of solvent.
      2. The unit used in the laboratory is mOsm (milliosmole).
  3. Use of the osmolality/osmolarity:
    1. It can monitor renal concentration ability for the course of renal disease.
    2. It can monitor fluid and electrolyte therapy.
    3. It can differentiate between hypernatremia and hyponatremia.
    4. It evaluates the secretion and renal response to ADH.
    5. There is a need to get the osmolarity of the serum and the urine.
  4. Normal:
    1. 500 to 800 mOsm/ kg of water.
    2. Serum osmolarity = 275 to 300 mOsm.
    3. Urine osmolarity = 50 to 1400 mOsm.

Volume

  1. The urine volume depends on the amount of water excreted by the kidneys.
  2. The volume of the urine depends upon:
    1. The fluid  (water) intake.
    2. Fluid (water) loss from nonrenal sources.
    3. The amount of ADH secretion.
    4. Excretion of dissolved solids such as glucose or salts.
  3. The urine volume excreted indicates the balance between fluid ingestion and water loss from the lungs, sweat, and intestine.
  4. Normal:
    1. 1200 to 1500 mL/24 hours.
    2. The range of 600 to 2000 mL/24 hours may be considered normal.
    3. The average urine volume is 1200 ml.
  5. Night urine volume is usually less in amount.
  6. The ratio of day urine to night’s urine is  2: 1 to 4:1.
  7. Nocturnal polyuria:
    1. There is increased urine at night. This may be seen in diabetes mellitus and diabetes inspidus.
    2. This may be seen as diuretics, or intake of tea, coffee, or alcohol. These will suppress the ADH.
  8. Polyuria is seen in:
    1. diabetes mellitus.
    2. Diabetes inspidus.
    3. Chronic renal disease.
    4. In the case of acromegaly.
    5. In the case of myxedema.
  9. Oliguria:
    1. There is a decrease in the normal daily urine volume.
      1. Anuria or oliguria, where urine volume is <200 mL/day.
    2. This is seen in dehydration due to vomiting, diarrhea, perspiration, or severe burn.
    3. Nephritis.
    4. Urinary tract obstruction.
    5. Acute renal failure.
    6. Oliguria may lead to anuria.
    7. Drugs that have diuretic effects are:
      1. Thiazides.
      2. Alcohol.
      3. Caffeine.
    8. The drugs which decrease the volume and are nephrotoxic are:
      1. Analgesics like salicylates.
      2. Antibiotics like neomycin, penicillin, and streptomycin.

Normal volume of the urine

Age Normal volume
Newborn
                1 to 2 days 30 to 60 mL/24 hours
Infant
              3 to 10 days 100 to 300 mL/24 hours
              60 to 365 days 400 to 500 mL/24hours
Child
               1 to 3 years 500 to 600 mL/24 hours
              8 to 14 years 800 o 1400 mL/24 hours
Adult
                 Male 800 to 1800 mL/24 hours
                 Female 600 to 1600 mL/24 hours
Elderly 250 to 2400 mL/24 hours

 

Urine analysis summary

Urine analysis summary

Normal urine picture:

Physical features Chemical features Microscopic findings
  1. Color = Pale yellow or amber
  2. Appearance = Clear to slightly hazy
  3. pH = 4.5 to 8.0
  4. Specific gravity = 1.015 to 1.025
  1. Blood = Negative
  2. Glucose = Negative
  3. Ketones= Negative
  4. Protein = Negative
  5. Bilirubin = Negative
  6. Urobilinogen = Negative (±)
  7. Leucocyte esterase = Negative
  8. Nitrite for bacteria = Negative
  1. RBCs = Rare or Negative
  2. WBC = Rare or Negative
  3. Epithelial cells = Few
  4. Cast = Negative (Occasional hyaline)
  5. Crystal = Negative (Depends upon the pH of the urine)
  6. Bacteria = Negative

Questions and answers:

Question 1: What is the difference between osmolality and osmolarity?
Show answer
Osmolality is the number of solute particles in one Kg of solvent. While Osmolarity is the number of solute particles in one liter of the solvent.
Question 2: What is the specific gravity to rule out that the sample is not urine?
Show answer
When the specific gravity is <1.003, most likely not urine.
Question 3: What is normal urine volume in infants of 1 to 2 days?
Show answer
It is 30 to 60 mL/24 hours.

Note: Details are seen in Part 3 urine complete analysis.


Possible References Used
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Comments

Dr Dipak Gadade Reply
January 17, 2021

Really nice collection of tests

Dr Dipak Gadade Reply
January 17, 2021

Loved it, using for my students

Dr. Riaz Reply
January 18, 2021

You are welcome.

Dr. Riaz Reply
January 18, 2021

dr. Dipak please see this link, https://www.labpedia.net/urine-analysis-part-3-complete-urine-analysis/

Dr. Riaz Reply
January 18, 2021

Thanks

chandu chandu Reply
September 6, 2021

thank you sir, great informative article for for every patient

Dr. Riaz Reply
September 6, 2021

Thank you.

Anacaona Reply
December 1, 2021

This was incredibly helpful! It would be amazing and refreshing to have you as a professor! Thank you kindly for sharing your wisdom!!

Dr. Riaz Reply
December 1, 2021

Thanks for the beautiful words.

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