Physical and Chemical Examination of Urine

Vocabulary flashcards covering the historical background, formation, composition, physical properties, and chemical analysis of urine based on Chapters 5 and 6.

Urea

The major organic solute in urine resulting from protein and amino acid breakdown, making up approximately one half of the dissolved solids.

Polyuria

Excessive urine production, typically over $2.5\,L$ per day.

Oliguria

Decreased urine output, usually less than $500\,mL$ in $24$ hours.

Anuria

Absence of urine output, defined as less than $50\,mL$ in $24$ hours.

Isothenuria

The inability of the kidneys to change the specific gravity of plasma ultrafiltrate, which remains at $1.010$.

Diuresis

Increased production of urine, often used interchangeably with polyuria.

Nocturia

An increased need to urinate at night.

Urochrome

A lipid-soluble pigment in plasma excreted in urine that gives it its normal yellow color.

Specific Gravity (SG)

An expression of concentration in terms of density; the ratio of urine density to the density of an equal volume of pure water.

Osmolality

The concentration of a solution expressed as osmoles of solute particles per kilogram ($kg$) of water.

Normal Urine Osmolality

A range between $275$ and $900\,mOsm/kg$.

Normal Serum Osmolality

A relatively constant range between $275$ and $300\,mOsm/kg$.

Hematuria

The presence of red blood cells (RBCs) in the urine.

Hemoglobinuria

The presence of free hemoglobin in the urine.

Leukocyte Esterase

An enzyme released by lysed white blood cells; its detection in urine indicates a pathologic process when WBC counts exceed $20/\mu l$.

Glucose Renal Threshold

The plasma level at which glucose appears in the urine, generally between $160$ and $180\,mg/dL$.

Benedict’s copper reduction test

The principle behind testing for reducing substances, including sugars like galactose (except sucrose), ascorbic acid, and cysteine.

Ketones

Breakdown products from large amounts of fatty acids, consisting of acetoacetate, acetone, and $\beta$-hydroxybutyrate.

Conjugated Bilirubin

The only form of bilirubin that is water-soluble and can be found in the urine; also known as direct bilirubin.

Urobilinogen

A product of bilirubin formed in the intestines; its presence in urine can indicate hemolytic anemia, cirrhosis, or hepatitis.

Ictotest

A tablet test used for the detection of bilirubin that is often more sensitive than the reagent strip method.

Acetotest

A tablet test used to confirm the presence of ketones.

What was significant about the contributions of Hippocrates to laboratory medicine in the fifth century BC?

Hippocrates wrote a uroscopy book that documented the analysis of urine based on color, clarity, odor, viscosity, and sweetness, laying foundational principles for laboratory medicine.

What is the average daily urine output, and how much plasma do the kidneys convert to ultrafiltrate?

The kidneys convert approximately 180,000 mL of filtered plasma into an average daily urine output of 1200 mL.

What is the main composition of urine?

Urine is composed of approximately 95% water and 5% solutes such as urea, inorganic ions, and other substances.

What is the major organic solute found in urine?

The major organic solute in urine is urea, resulting from the breakdown of proteins and amino acids, making up approximately one half of the dissolved solids.

Which inorganic ions are commonly found in urine?

Common inorganic ions in urine include chloride, sodium, and potassium.

What indicates that a fluid is urine?

High levels of urea and creatinine are indicative of a fluid being urine.

What additional components may be found in urine, and what do their increases indicate?

Urine may also contain cells, crystals, mucus, and bacteria; increases in these components can indicate disease.

What determines urine volume?

Urine volume is determined by the body's state of hydration.

What is polyuria?

Polyuria is excessive urine production, typically over $2.5$ liters per day.

What is oliguria?

Oliguria is decreased urine output, usually less than $500$ mL in $24$ hours.

What is anuria?

Anuria is the absence of urine output, defined as less than $50$ mL in $24$ hours.

What is diuresis?

Diuresis is the increased production of urine, often used interchangeably with polyuria.

What is nocturia?

Nocturia is an increased need to urinate at night.

What is isothenuria?

Isothenuria is the inability of kidneys to change the specific gravity of plasma ultrafiltrate, which remains at $1.010$.

What determines the normal color of urine?

The normal color of urine is yellow due to the presence of urochrome, a lipid-soluble pigment in plasma excreted in urine.

What does dark yellow urine indicate?

Dark yellow urine typically indicates concentrated urine.

What does pale yellow urine indicate?

Pale yellow urine usually indicates dilute urine.

What should be referred to when describing urine color?

Standard terms are used to describe urine color; refer to laboratory's policies and procedures.

What substances can change urine color?

Substances that can change urine color include blood, myoglobin, bilirubin, porphyrins, melanin, indican (derived from tryptophan), and homogentisic acid.

What does the presence of blood in urine indicate?

The presence of blood in urine, known as hematuria, can indicate various medical conditions including infection, stones, or injury.

What does myoglobin in urine indicate?

Myoglobin in urine can indicate muscle injury or conditions such as rhabdomyolysis.

What does bilirubin in urine signify?

Bilirubin in urine can indicate liver disease, bile duct obstruction, or hemolysis.

What are porphyrins and how do they affect urine color?

Porphyrins are compounds related to heme production; their presence can indicate conditions like porphyria, leading to dark urine.

What is the significance of melanin in urine?

Melanin in urine can indicate melanoma or other conditions producing excessive pigmentation.

What role does indican play in urine color?

Indican, derived from tryptophan, can cause urine to appear dark blue or purple, an indication of certain metabolic disorders.

What is homogentisic acid and its effect on urine color?

Homogentisic acid can darken urine, often associated with a condition called alkaptonuria, where the body cannot properly break down tyrosine and phenylalanine.

What types of ingested substances can alter urine color?

Ingested substances that can alter urine color include medications, dyes, vitamins, and pigmented foods like beets or berries.

What does white foam in urine indicate?

Normal urine when shaken will produce white foam that rapidly dissipates; stable white foam indicates large amounts of albumin in urine.

What does yellow foam in urine signify?

Yellow foam caused by increased bilirubin in urine, which can indicate liver disease or bile duct obstruction.

What does clarity refer to in urine analysis?

Clarity describes the cloudiness of urine caused by suspended particulate matter that scatters light.

What is the normal clarity of urine?

Normal specimens of urine are clear.

What are common causes of cloudiness in urine?

Causes of cloudiness include contamination from skin or vaginal secretions, bacterial growth, fecal material, precipitation of dissolved solutes, x-ray contrast media, and the presence of red blood cells (RBCs), white blood cells (WBCs), epithelial cells, clots, bacteria, or casts.

What is the normal odor of urine?

Normal urine has an aromatic odor.

What causes urine to become odorous when standing?

Urine on standing becomes odorous due to bacterial conversion of urea to ammonia.

What can change the odor of urine?

Ingestion of certain foods or drugs can change the odor of urine.

What unusual odor is produced by ketones in urine?

Ketones produce a sweet or fruity smell in urine, often associated with diabetes or starvation.

What types of odors can amino acid disorders produce?

Amino acid disorders often produce odd odors in urine, indicating specific metabolic conditions.

What does concentration refer to in urine analysis?

Concentration refers to the amount of solutes present in a volume of water excreted in urine.

What is the typical composition of urine?

Urine normally consists of approximately 95% water and about 5% solutes.

What factors can affect the types of solutes found in urine?

The types of solutes in urine vary with the patient's diet, physical activity, and health status.

How is color related to urine concentration?

Color is a crude indicator of urine concentration, with darker colors typically indicating higher concentration of solutes.

What is specific gravity (SG) in urine analysis?

Specific gravity (SG) is an expression of concentration in terms of density; it measures the mass of solutes present per volume of solution.

How is specific gravity of urine determined?

Specific gravity is the ratio of urine density to the density of an equal volume of pure water under specific conditions.

What factors affect specific gravity measurements?

Both the number of solute particles and molecular size affect specific gravity in urine.

What is osmolality?

Osmolality is the concentration of a solution expressed in terms of osmoles of solute particles per kilogram (kg) of water.

What unit is often used for measuring osmolality in biological solutions?

Milliosmoles (mOsm) are often used for convenience due to the low osmolality of biological solutions.

What are the normal urine osmolality values?

Normal urine osmolality values range from $275$ to $900\,mOsm/kg$.

What are the normal serum osmolality values?

Normal serum osmolality values are relatively constant and range between $275$ and $300\,mOsm/kg$.

What factors affect urine osmolality?

Urine osmolality values depend on diet, fluid intake, and physical activity.

What are the principal uses of osmolality?

The principal uses of osmolality include evaluating renal concentrating ability of kidneys, monitoring renal disease, monitoring fluid and electrolyte balance, and differentially diagnosing the cause of polyuria.

How is osmolality determined?

Osmolality is determined by measuring a colligative property of a solution, such as freezing point depression or vapor pressure.

What are reagent strips used for in chemical analysis?

Reagent strips are the most common method for chemical testing, used to analyze various components in urine.

How do reagent strips work?

A plastic strip with reagent-impregnated pads is dipped in urine, resulting in a visual color change for analysis.

What do the results from reagent strips provide?

Reagent strips give qualitative results based on the color change of the pads after urination.

What are some interfering substances in urine analysis?

Interfering substances such as ascorbic acid need to be detected or eliminated during urine analysis using reagent strips.

Why are tablet/liquid tests used in urine analysis?

Tablet/liquid tests are used to confirm results obtained by reagent strip testing.

When might tablet tests be preferred over strip testing?

Tablet tests serve as an alternative method for highly pigmented urine.

What is a benefit of using Ictotest tablets?

Ictotest tablets for bilirubin are more sensitive than the strip testing method.

How does test specificity differ between methods?

Test specificity can differ from the strip method, such as in the case of the sulfosalicylic acid test.

What is the purpose of the Acetotest?

The Acetotest is used to confirm the presence of ketones in urine.

What is specific gravity (SG)?

Specific gravity (SG) is an expression of concentration in terms of density; it measures the mass of solutes present per volume of solution.

What is an indirect chemical method of measuring specific gravity?

Specific gravity can be measured indirectly through the concentration of ionic solutes present in the urine.

Which ionic solutes are measured by specific gravity methods?

Specific gravity methods only measure ionic solutes such as sodium (Na+), potassium (K+), chloride (Cl-), and ammonium (NH4+).

How does the reagent strip method measure specific gravity?

The reagent strip pad is impregnated with reagents that release protons when immersed in urine, changing the pad color in proportion to ionic concentration.

What is the normal pH range of urine?

Normal pH of urine varies from 4.5 to 8.0; it is usually slightly acidic but can become more alkaline after meals.

How does pH affect formed elements in urine?

pH can affect the stability of formed elements in urine, potentially influencing diagnostic results.

When should a pH test be performed on urine?

pH testing should be performed on fresh urine to ensure accuracy of results.

What is the principle of urine pH testing?

Urine pH testing is based on a double indicator system that uses bromothymol blue and methyl red, producing color changes from orange (pH 5.0) to green (pH 7.0) to blue (pH 9.0).

What is hematuria?

Hematuria is the presence of red blood cells (RBCs) in the urine.

What is hemoglobinuria?

Hemoglobinuria is the presence of free hemoglobin in the urine.

How does hemoglobinuria relate to myoglobin?

Hemoglobinuria detects hemoglobin, which can also indicate the presence of myoglobin in urine.

What is the principle behind detecting hemoglobinuria?

Detection is based on heme’s pseudoperoxidase activity, which reacts in a test.

How does the hemoglobinuria test work?

The pad has chromogen and peroxide; the pseudoperoxidase reduces peroxide, oxidizing the chromogen and causing a color change.

What substance is known to interfere with the hemoglobinuria test?

Ascorbic acid is known to interfere with the reaction in the hemoglobinuria test.

What is leukocyte esterase?

Leukocyte esterase is an enzyme released by lysed white blood cells (WBCs) that indicates the presence of WBCs in urine.

What is the normal number of white blood cells (WBCs) in urine?

Normally, few white blood cells (WBCs) are seen in urine; more than $20/\mu l$ is an indication of a pathologic process.

Why might WBCs not be seen in urine samples?

WBCs are susceptible to lysis, so they may not be visible in the urine but can still release leukocyte esterase.

What is the principle behind the leukocyte esterase test?

The test is based on the action of leukocyte esterase to cleave an ester in the pad, resulting in a color change; it can detect as few as 10 WBCs/μl.