Clinical Chem Urinalysis

Urinalysis

  • common laboratory test on urine sample
  • non-invasive procedure to check for the composition of urine
  • to screen, diagnose & monitor a wide range of health conditions/clinical disorders   * urinary tract infection, urologic disorders (e.g., calculi & malignancy), diabetes, kidney & liver diseases

Diagnostic Testing

Physical

  • volume   * closely regulated by kidneys   * reflects overall fluid homeostasis   * Polyuria     * urine volume > 2000ml/day     * due to osmotic diuresis in diabetes mellitus, hyperthyroidism & infections     * insufficient secretion of / inability to respond to antidiuretic hormone (ADH)     * lack of hormone aldosterone     * after urination, it burns     * excessive intake / infusion of fluid     * renal diseases where the kidneys fail to concentrate urine     * the use of diuretics, alcohol & caffeine   * Oliguria     * urine volume <500ml/day     * as a consequence of conditions that decrease plasma volume, lead to dehydration, have impaired renal functions   * Anuria     * urine volume <100ml/day for 2-3 days despite high fluid intake     * follows oliguria in shock; acute tubular necrosis caused by exposure to toxic agents
  • Colour   * normal: straw to dark-yellow colour   * presence of the pigment urochrome which is produced at a fairly constant rate   * colour intensity indirectly indicates urine concentration & state of hydration   * examine the urine sample under good light against a white background   * if the urine sample stands at room temperature, urochrome will increase & the colour may deepen
  • Odour (not routinely reported)   * normal: faintly aromatic odour   * as the urine specimen stands, the odour of ammonia predominates   * unusual odour is indicative of diseases states   * fruity odour: ketonuria resulting from uncontrolled diabetes mellitus   * “mousy” smell: associated with phenylketonuria   * sweet-smelling like maple syrup: maple syrup urine disease   * “fishy” odour: bacterial infection (e.g. urinary tract infection)
  • Clarity   * normal: clear or slightly cloudy   * via visual examination   * alkaline urine: precipitation of phosphates, carbonates   * acidic urine: precipitation of urates, uric acid, calcium oxalate   * foamy urine: presence of proteins   * substances that can cause cloudy urine: white blood cells, red blood cells, bacteria, fats   * may indicate inflammation or infection of kidneys, urinary & genital tracts, sexually transmitted diseases, kidney stones, diabetes
  • specific gravity   * density of liquid compared with that of a similar volume of distilled water, when both solutions are at the same or similar temperature   * indicate the kidney’s ability to reabsorb water & chemical substances from the glomerular filtrate   * normal: >1.000 (1.002-1.035)   * influenced by the number and size of particles present     * e.g. ↑USG with the presence of large amount of glucose and proteins   * low USG: overhydration, diabetes insipidus, acute tubular necrosis, pyelonephritis   * high USG: dehydration, uncontrolled diabetes mellitus, acute glomerulonepritis, heart & liver failure   * constant fixed USG of 1.010 regardless of fluid intake     * chronic glomerulonephritis with severe renal damage     * loss of urine concentrating ability   * as a preliminary rapid screening of urine concentration   * urine osmolality → more reliable & accurate to evaluate kidney function, particularly the concentrating ability

Chemical

pH

  • normal range: 4.5 - 8.0
  • reflects the kidneys’ ability to regulate acid-base balance
  • through regulation of hydrogen ions excretion
  • only reliable when testing on freshly voided specimen
  • influenced by diet & medications
Alkaline urine (pH >7.0)
  • due to respiratory/metabolic alkalosis, presence of urease-producing bacteria, renal tubular acidosis, urinary tract infection
  • promotes calcium-phosphate precipitation
  • vegetarian diet, diets high in citrate, drugs i.e., sodium bicarbonate, potassium citrate & acetazolamide
Acidic urine (pH <7.0)
  • diabetes mellitus, diabetes ketoacidosis, diarrhea, emphysema
  • promotes the formation of uric acid & cystine kidney stones
  • high-protein diet, intake of acidic fruits (e.g., cranberries), drugs (e.g., ammonium chloride)

\

Red blood cells (RBCs)

  • normal: negative/<5 RBCs per ml
  • Indications:   * tumours/trauma/infections/inflammation in genitourinary tract   * pyelonephritis, lupus nephritis, kidney stones, renal hypertension   * non-renal: hemorrhagic disorder, exposure to toxic chemicals, strenuous exercise
Hematuria
  • presence of 3 or more RBCs per high-powered field in 2 of three urine samples

\

White blood cells (WBCs)

  • normal: only a few
  • Indications:   * bacterial infection in renal/genitourinary system, i.e., cystitis, pyelonephritis   * other non-infectious inflammatory disorders, e.g., glomerulonephritis & lupus nephritis   * presence of tumours and renal calculi
Pyuria
  • excessive amount of WBCs in urine   * \     > 5 WBCs per high-powered field is considered abnormal

\

Proteins

  • normal: only in trace amount (<150 mg/day or 10mg/dL)
  • Indications:   * physiological: strenuous exercise, dehydration   * renal diseases/failure: e.g., nephrosis, glomerulonephritis, polycystic kidney disease   * systemic disorders leading to increased level of serum proteins: e.g., multiple myeloma
Proteinuria (Albuminuria)
  • elevated proteins in the urine
  • ~1/3 of the total urinary proteins is albumin
  • other proteins: Tamm-Horsfall mucoproteins (secreted by distal renal tubule), immunogloblin light chains, microglobulin, etc.

\

Glucose

  • normal: negative
  • Indications:   * diabetes mellitus, Cushing;s syndrome, Fanconi’s syndrome, liver & pancreatic diseases   * rare hereditary metabolic disorders   * gestational diabetes
Glycosuria
  • the presence of reducing sugars in urine
Glucosuria
  • presence of glucose in urine (most common type of ==GLYCOSURIA==)

\

Ketones

  • normal: negative
  • Indications:   * pregnancy, ketogenic diets, compromised nutritional intake   * uncontrolled diabetes mellitus (diabetic ketoacidosis), liver disease, certain forms of glycogen storage disease
Ketonuria
  • high level of ketones in the urine

\

Bilirubin

  • normal: negative
  • Indications:   * liver dysfunction (due to obstructive jaundice, cirrhosis, viral- or drug-induced hepatitis, hepatotoxic drugs, toxins)   * biliary obstruction   * congenital hyperbilirubinemia

\

Urobilinogen

  • normal: 0.1mg/dL - 1.0 mg/dL or 4mg/day
  • Indications:   * ↑in hemolysis, hepatocellular disease (e.g., cirrhosis, hepatitis), severe infection   * ↓in bile duct obstruction, renal insufficiency, with antibiotic use

\

Leukocyte esterase

  • normal: negative
  • Indications:   * presence of neutrophils, either due to infection or other inflammatory processes, in urinary tract or kidneys

\

Nitrites

  • normal: negative
  • Indications:   * presence of a significant number of bacteria, and a urine culture should be performed   * UTI caused by nitrate reductase positive bacteria

\

Microscopical

  • should be performed among those with persistent hematuria or proteinuria

Cells

red blood cells
  • 0-5 cells/high power field
  • confirming hematuria following positive dipstick results
  • presence of dysmorphic red blood cells is suggestive of glomerular diseases
white blood cells
  • 0-5 cells/high-power field (under high-power magnification)
  • may also be examined under low-power magnification
  • indicative of UTI, but culture is still needed for confirmation
epithelial cells
  • increased squamous epithelial cells: originate from vagina, suggestive of contamination
  • transitional epithelial cells: normal
  • increased renal tubule cells: acute tubular necrosis & renal pathology associated to nephrotoxic agents

Casts

  • formed in the lumen of distal convoluted tubules & collecting ducts
  • via agglutination of protein cells or cellular debris
  • coagulum consists of Tamm-Horsfall mucoprotein with or without additional elements
  • prompt testing is mandatory (as it is dissolved in acidic urine within 30min or 10min in alkaline urine)

 

Crystals

  • commonly found in urine; may or may not be pathologic
  • supersaturation of solute componentys in urine initiates the crystallization
  • acidic urine: calcium oxalate, uric acid & amorphous urate crystals
  • alkaline urine: calcium phosphate, amorphous phosphate & ammonium magnesium phosphate crystals
  • cystine crystals: abnormal; in those who have cystinuria & kidney stones
  • tyrosine & leucine crystals: abnormal; suggestive of severe liver diseases

Bacteria

  • absent in urine of normal healthy individuals
  • reflects genitourinary tract infection or contamination of external genitalia

Dipstick

  • results are available almost immediately
  • convenient and cost-effective test to be performed at urgent care facilities, emergency departments, clinics or event at home

Fecal Analysis

  • collected in a plastic hat-type receptacle
  • should not be contaminated with urine or water
  • should include any visible blood, mucus, pus, or parasites
  • should be sent to the laboratory within 30-60 mins

Microscopial

Leukocytes
  • especially neutrophils and monocytes
  • as initial evaluation of diarrhoea of unknown aetiology/cause
Epithelial cells
  • large amount indicates intestinal mucosa is irritated
Fats
  • in the forms of triglycerides, fatty acids & fatty acid salts
  • coupled with staining techniques prior to microscopic examination
  • steatorrhea → excess fats in the stool (>60 fat droplets per high-power field)
  • due to malabsorption syndromes or deficiency in pancreatic enzymes
  • non-pathological: surgical resection of intestines & recent intake of excessive amounts of dietary fats
Meat fibers
  • assess the efficiency of digestion
  • presence in the stools indicates inadequate proteolysis
  • usually correlates positively with steatorrhea
Parasites
  • among individuals with intestinal disorders of unknown etiology or history of possible exposure to parasites
  • i.e., roundworms, tapeworms, hookworms, & protozoa
  • must be transported immediately to the lab

Chemical tests

Occult blood
  • most frequently preformed
  • to detect carcinoma
  • numerous other pathological conditions, e.g., peptic ulcer, gastritis, inflammatory bowel diseases, diverticular diseases, hemmorrhoids, anorectal fissure, etc.
  • stool samples are obtained after bowel movement or during rectal examination
  • follow meat-free, high-bulk diet for 3 days before testing
  • stop taking drugs that might alter the test results
Quantitative fats
  • definitive test for excessive fecal fats
  • evaluation is performed over 72-hour period
  • controlled diet = percentage of solid material
  • elevated level indicates intestinal malabsorption or pancreatic insufficiency
Trypsin
  • normally not present in stool, except children <2 years old
  • absence in children <2 years of age indicates pancreatic deficiency
Carbohydrates
  • related to malabsorption disorders, e.g., celiac diseases
  • excessive amounts appear in the stool
  • evaluation: oral & intravenous (IV) glucose tolerance tests, and compare the results
  • carbohydrate malabsorption syndrome   * normal on IV but not on oral glucose tolerance test
Urobilinogen
  • rarely assessed on stool sample
  • blood and urine samples are more commonly used
  • ↓ in liver & biliary tract disorders; ↑in hemolytic anemia
Bile
  • absent in faeces of normal adults
  • otherwise occurs with diarrhea & hemolytic anemias

Microbiologic

Stool cultures
  • evaluate diarrhea of unknown etiology or other systemic infections
  • identify pathological types of bacteria
  • sampling via rectal swab or during bowel movement
  • must not be exposed to air or room temperature more than necessary

\