The importance of urine testing in the clinical laboratory

PFC Eaker

How is urine produced?

Produced by the kidneysDrained by ureter into bladderUrethra brings out urine from bladder

Kidneys

Nephrons

Structural and functional unit of the kidneyEliminates wastesRegulates pH, blood pressure and blood

volume

Nephrons

Glomerulus

Basic filtration unit of the kidneyFirst place where urine is formed in the

bodyAlong with the Bowman’s capsule,

comprises the renal corpuscleOverall function of the kidney is measured

by the glomerular filtration rate (GFR), which is the rate that blood is filtered through all glomeruli

Glomerulus

Glomerulus

Bowman’s capsule

Glomerulus

Afferent arteriole

Glomerulus

Efferent arteriole

Glomerulus

Proximal convoluted tubule

How is this process controlled?

Anti diuretic hormone (ADH) Concentration of water in the blood decreases Increase in the osmotic pressure stimulates the

osmoreceptors in the hypothalamus Hypothalamus signals the posterior pituitary gland to

secrete ADH Blood carries ADH to the kidneys ADH causes the distal convoluted tubules and collecting

ducts to increase water absorption through osmosis Urine becomes more concentrated and volume decreases

Normal composition

95% water0.4% Sodium0.05% Ammonia0.6% Phosphates2% Urea0.2% SulfateCreatine and Urobilinogen in minute

amounts

What can urine indicate?

UTISystemic illnessMetabolic disordersDiabetesPregnancy

Symptoms or problems

Dark, strong smelling urineBurning urinationOliguria, Polyuria, AnuriaGlycosuria, Haematuria, SemonorrhoeaBackache, Lower abdominal pain,

Suprapubic pain

Clinical tests

Reagent strips

Clinical tests

Protein Blood Leukocytes Nitrite Glucose Ketone pH Specific gravity Bilirubin Urobilinogen

Protein

Expected Values: <15mg/dl Sensitivity: 15-30mg/dl Albumin Limitations: A visibly bloody urine

may cause falsely elevated

results

Blood

Expected values: <0.010 mg/dl or 3 rbc/ul Sensitivity: 0.015-0.062 mg/dl Limitations: Some medications

may cause false positives

Leukocytes

Expected values: <10 leukocytes Sensitivity: 5-15 leukocytes Limitations: Elevated glucose,

medications, and contamination

may cause false results

Nitrite

Expected values: <0.075mg/dl Sensitivity: 0.06-0.1 mg/dl Limitations: Negative results do

not rule out significant bacteriuria

Glucose

Expected values: <30mg/dl Sensitivity: 75-125 mg/dl Limitations: Ketone bodies reduce

sensitivity of the test

Ketone

Expected values: <2mg/dl Sensitivity: 5-10 mg/dl Limitations: Highly pigmented

urine may cause false trace

results

pH

Expected values: 4.6-8.0 Sensitivity: 5-8.5 Limitations: Bacterial growth may

cause alkaline shift (pH >8.0)

Specific Gravity

Expected values: 1.001-1.035 Sensitivity: 1.000-1.030 Limitations: Dependent upon ions

in urine

Bilirubin

Expected values: ~0.02mg/dl Sensitivity: 0.4-0.8 mg/dl Limitations: bilirubin derived

bile pigments may mask the

bilirubin reaction

Urobilinogen

Expected values: <1.0 mg/dl Sensitivity: >0.02 mg/dl Limitations: Test pad may react

with interfering substances known

to react with Ehrlich’s reagent

Confirmation tests

IctotestAcetestClinitest

Confirmation tests

IctotestConfirmation test for bilirubinReaction based on combining

a solid diazonium salt with

bilirubin

Confirmation tests

AcetestConfirmation test for ketonesAcetoacetic acid or acetone

in urine or blood reacts with

nitroprusside in presence

of glycine

Confirmation tests

Clinitest Used to determine amount of reducing substances

(glucose) in urine Copper sulfate in tablet reacts with

reducing substances in urine

converting cupric sulfate to cuprous

oxide 5-drop method 2-drop method

Questions