URINALYSIS

Prakash

B.Sc.MLT Prat- II

Urine formation

In an adult, urine output volume ranges from 400 to 2,000 mL/day.

Overview.

◻ Approximately 1,200 mL of blood per minute (i.e., 20%–25% of blood volume) is supplied to the kidneys through the renal artery, which branches into the afferent arterioles and efferent arterioles.

Constituents of urine◻ Urine is continuously formed by the kidneys. Depending on dietary

intake, physical activity, metabolism and endocrine function,concentrations of urine constituents vary.

◻ The largest component of urine is water.◻ Urea accounts for half of the total dissolved solids in urine (6–18

g/24 h). It isa metabolic waste product from the breakdown of protein and amino acids in the liver.

◻ Other organic compounds in urine are creatinine (0.3–0.8 g/24 h) and uric acid(0.08–0.2 g/24 h). A fluid can be identified as urine if it contains a high concentration of urea and creatinine.

◻ Chloride (100–250 mEq/24 h) is the major inorganic solid dissolved in urine, followed by sodium (100–200 mEq/24 h) and potassium (50–70 mEq/24 h).

◻ In urinary sediment, a few squamous, transitional, and renal epithelial cells per high power field (40X) as well as one to two red blood cells (RBCs) or one to five white blood cells (WBCs) are considered normal findings.

THE URINE SPECIMEN◻ Routine urinalysis testing describes the results of a series of screening

tests capable of detecting (in a semi-quantitative manner) renal,urinary tract, metabolic and systemic diseases. Urine is readilyavailable and easy to collect.

1. When there is disease of the kidney or bladder, kidney function may beimpaired. Substances that are normally retained by the kidney may beexcreted, and substances that are normally excreted may be retained.The routine urinalysis is a good screening test for the detection ofchanges in renal system.

2. Metabolic or systemic diseases may lead to the excretion ofsubstances such as abnormal amounts of metabolic end products orsubstances specific for a particular disease that can be detected inurine. The amount of sodium or water that is excreted is also indicativeof systemic or metabolic disease.

3. All body fluid specimens should be considered infectious and collected,transported, and handled according to safety protocols.

4. Urine specimens should be analyzed within 1 hour of collection, or theymust be stored in a dark refrigerator between 4◦C and 7◦C to preservechemical and cellular constituents.

Random Specimen

◻ This is the most commonly received specimen because of its ease of collection and convenience for the patient.

◻ The random specimen may be collected at any time, but the actual time of voiding should be recorded on the container.

◻ The random specimen is useful for routine screening tests to detect obvious abnormalities

First Morning Specimen

◻ The first morning specimen, or 8-hour specimen, is a concentrated specimen, thereby assuring detection of chemicals and formed elements that may not be present in a dilute random specimen.

◻ The patient should be instructed to collect the specimen immediately on arising and to deliver it to the laboratory within 2 hours.

◻ It is also essential for preventing false-negative pregnancy tests and for evaluating orthostatic proteinuria.

24-Hour (Timed) Specimen Collection

Procedure◻ Provide patient with written instructions, and explain

collection procedure.◻ Issue proper collection container and preservative.◻ Day 1: 7 a.m.: patient voids and discards specimen; collects

all urine for the next 24 hours.◻ Day 2: 7 a.m.: patient voids and adds this urine to previously

collected urine.◻ On arrival at laboratory, the entire 24-hour specimen is

thoroughly mixed, and the volume is measured and recorded.

◻ An aliquot is saved for testing and additional or repeat testing; discard remaining urine.

◻ Measuring the exact amount of a urine chemical is often necessary instead of just reporting its presence or absence.

◻ A carefully timed specimen must be used to produce accurate quantitative results.

◻ A 24-hour specimen must be thoroughly mixed and the volume accurately measured and recorded.

Urine PreservativesPreservatives Advantages Disadvantages Additional Information

Refrigeration Does not interfere withchemical tests

Raises specific gravity by hydrometerPrecipitates amorphousphosphates and urates

Prevents bacterial growth24 h

Thymol Preserves glucose andsediments well

Interferes with acid precipitation tests for protein

Boric acid Does not interfere with routine analyses other than pH.Preserves protein and formed elements well

May precipitate crystals when used in large amounts

Keeps pH at about 6.0. Is bacteriostatic (not bactericidal) at 18 g/L; can use for culture transport Interferes with drug and hormone analyses

Formalin(formaldehyde

Excellent sediment preservative

Acts as a reducing agent, interfering with chemical tests for glucose, blood, leukocyte esterase, and copper reduction

Rinse specimen containerwith formalin to preservecells and casts

Toluene Does not interfere withroutine tests

Floats on surface of specimens and clings to pipettes and testing

Chemical Examination of Urine

◻ pH

◻ Specific Gravity

◻ Protein

◻ Glucose

◻ Ketone

◻ Bilirubin

◻ Urobilinogen

pH

◻ To differentiate pH units double-indicator system of methyl red and bromthymol blue.

◻ Methyl red produces a color change from red to yellow in the pH range 4 to 6, and bromthymol blue turns from yellow to blue in the range of 6 to 9.

◻ Therefore, in the pH range 5 to 9 measured by the reagent strips, one sees colors progressing from orange at pH 5 through yellow and green to a final deep blue at pH 9.

Methyl red H+ → Bromthymol blue H+

(Red-Orange → Yellow) (Green → Blue)

Physical Examination of Urine

◻ Volume

◻ Colour

◻ Odur

Volume

◻ Normal : 1.2 – 2 L/Day

◻ Polyuria : >2000ml/Day

◻ Oliguria : >500ml/Day

◻ Anuria : Total suppression of urine <100ml

Color

Odur Causesof Urine

Odor Cause

Aromatic Normal

Foul , ammonia-like Bacterial decomposition urinary tract infection

Fruity, sweet Ketones (diabetes mellitus,starvation, vomiting

Maple syrup Maple syrup urine disease

Mousy Phenylketonuria

Rancid Tyrosinemia

Cabbage Methionine malabsorption

Clinical Significance of Urine pH

1. Respiratory or metabolic acidosis/ketosis

2. Respiratory or metabolic alkalosis

3. Defects in renal tubular secretion and reabsorption of acids and bases—renal tubular acidosis

4. Renal calculi formation

5.Treatment of urinary tract infections

6. Precipitation/identification of crystals

7. Determination of unsatisfactory specimens

Specific Gravity

◻ Reaction is based on the change in pka (dissociation constant) of a polyelectrolyte in an alkaline medium.

◻ The polyelectrolyte ionizes, releasing hydrogen ions in proportion to the number of ions in the solution.

◻ The higher the concentration of urine, the more hydrogen ions are released, thereby lowering the pH. Incorporation of the indicator bromthymol blue on the reagent pad measures the change in pH.

◻ As the specific gravity increases, the indicator changes from blue (1.000 [alkaline]), through shades of green, to yellow (1.030 [acid]).

◻ Readings can be made in 0.005 intervals by careful comparison with the color chart.

Clinical Significance of Urine Specific Gravity

1. Monitoring patient hydration and dehydration

2. Loss of renal tubular concentrating ability

3. Diabetes insipidus

4. Determination of unsatisfactory specimens due to low concentration

Protein

◻ The general belief that indicators produce specific colors in response to particular pH levels, certain indicators change color in the presence of protein even though the pH of the medium remains constant.

◻ This is because protein (primarily albumin) accepts hydrogen ions from the indicator.

◻ The test is more sensitive to albumin because albumin contains more amino groups to accept the hydrogen ions than other proteins

◻ Tetrabromphenol blue and an acid buffer to maintain the pH at a constant level.

◻ At a pH level of 3, both indicators appear yellow in the absence of protein; however, as the protein concentration increases, the color progresses through various shades of green and finally to blue.

◻ Readings are reported in terms of negative, trace, 1, 2, 3, and 4

Clinical Significance of Urine Protein

Prerenal Tubular DisordersIntravascular hemolysis Fanconi syndromeMuscle injury Toxic agents/heavy metalsAcute phase reactants Severe viral infectionsMultiple myelomaRenal PostrenalGlomerular disorders Lower urinary tract

infections/ inflammationImmune complex Injury/traumadisordersMenstrual contaminationAmyloidosis Prostatic fluid/spermatozoaToxic agents Vaginal secretionsDiabetic nephropathyStrenuous exerciseDehydrationHypertensionPre-eclampsia

Glucose

Glucose Oxidase Reactions

◻ In the first step, glucose oxidase catalyzes a reaction between glucose and room air to produce gluconic acid and peroxide.

◻ In the second step, peroxidase catalyzes the reaction between peroxide and chromogen to form an oxidized colored compound that represents the presence of glucose.

Clinical Significance of Urine Glucose

Hyperglycemia- Associated◻ Diabetes mellitus◻ Pancreatitis◻ Pancreatic cancer◻ Acromegaly◻ Cushing syndrome◻ Hyperthyroidism◻ Pheochromocytoma◻ Central nervous system

damage◻ Stress◻ Gestational diabetes

Renal-AssociatedFanconi syndromeAdvanced renal diseaseOsteomalaciaPregnancy

Ketones

The sodium nitroprusside (nitroferricyanide) reaction◻ In this reaction, acetoacetic acid in an alkaline medium reacts with

sodium nitroprusside to produce a purple color.

◻ The test does not measure beta-hydroxybutyric acid and is only slightly sensitive to acetone when glycine is also present; however, inasmuch as these compounds are derived from acetoacetic acid, their presence can be assumed, and it is not necessary to perform individual tests.

◻ Results are reported qualitatively as

negative, trace, small (1), moderate (2), or large (3), .

alkaline acetoacetate + sodium nitroprusside + (glycine) → purple color

(and acetone)

Clinical Significance of Urine Ketones

1. Diabetic acidosis

2. Insulin dosage monitoring

3. Starvation

4. Malabsorption/pancreatic disorders

5. Strenuous exercise

6.Vomiting

7. Inborn errors of amino acid metabolism

Bilirubin

◻ THE DIAZO REACTION

◻ Bilirubin combines with 2,4-dichloroaniline diazonium salt or 2,6-dichlorobenzene-diazonium-tetrafluoroborate in an acid medium to produce an azodye, with colors ranging from increasing degrees of tan or pink to violet, respectively.

◻ Qualitative results are reported as

negative, small, moderate, or large, or as negative, 1+, 2+, or3+.

bilirubin glucuronide + diazonium salt azodye

acid

Clinical Significance of Urine Bilirubin

1. Hepatitis

2. Cirrhosis

3. Other liver disorders

4. Biliary obstruction (gallstones, carcinoma)

Urobilinogen

◻ Ehrlich’s aldehyde reaction ◻ In which urobilinogen reacts with p-dimethylaminobenzaldehyde

(Ehrlich reagent) to produce colors ranging from light to dark pink.

urobilinogen + p-dimethylaminobenzaldehyde → red color(Ehrlich reagent (Ehrlich reagent)

reactive

substances)

Clinical Significance of Urine Urobilinogen

1. Early detection of liver disease

2. Liver disorders, hepatitis, cirrhosis, carcinoma

3. Hemolytic disorders