Clinical Microscopy

• Urine collection and testing

  • delivery to lab and tested within 1 hour
  • preservation - must be if not tested within 1 hour
  • refrigeration - 4-6 degrees C; most common; prevents bacterial growth for 24 hours; if urine turns cloudy, indicates formation of amorphous sediment
• nitrites reaction

  • reagent strip - Greiss reaction
  • qualitative test, not quantitative, strictly positive or negative
  • test is calibrated to not change for contamination quantities
• the renal system

  • secretes some hormones
  • erythropoietin - stimulates RBC production
  • renin - regulates blood pressure
• the renal system

  • helps to regulate acid/base balance
  • manipulation of bicarbonate, hydrogen ions, metabolic acids
• normal urine

  • urine should be sterile
  • sterile - bc urinary tract is sterile; not sterile if NF in it, UTI occurs and contaminates urine
• normal urine

  • contains - water, urea (biproduct of protein metabolism), creatinine, Cl-, Na+, K+, PO4, SO4, NO3-
• normal urine

  • may also contain small amounts of
  • cells (squamous epithelium) casts (cylindrical protein structures after strenuous exercise); crystals (can be normal if hydrated); bacteria (skin flora contaminant)
• glomerulonephritis

  often caused by Ab-Ag complexes from infections at other body sites e.g. Group A strep infection, syphilis, some autoimmune disorders
• nephrotic syndrome

  results in massive proteinuria; see increase in serum lipids, decrease in serum albumin; often caused by circulatory disorders taht affect blood flow to kidney
• Orange urine

  • Interferes with dipstick reactions
  • have to do manually - protein, specific gravity, etc
• urinometer

  • must be manually calibrated
  • needs temperature correction
  • floats/sinks based on density of urine
• refractometer-

  • correction is needed for high glucose and proteins
• sg dipstick

  • principle - reagents have acid groups that dissociate and bromothymol blue indicator
• sg dipstick

  • color indicator
  • blue green - low specific gravity
  • greenish - neutral sg
  • yellow/orange - high sg
• sulfosalicylic acid precipitation

  • will pick up Bence-Jones proteins in multiple myloma
  • excess light chains
• glucose

  • confirmatory testing
  • reducing tabs - detects reducing sugars
  • if positive for glucose, will be positive, even if there are reducing sugars
  • clinitest done in all children with negative glucose
• glucose dipstick

  • specificity for glucose and interferences
  • another reducing sugars won't be picked up
  • false negative if Vitamin C is high in urine
• ketones

  • types
  • acetone
  • acetoacetic (diacetic) acid
  • beta hydroxylacetic acid
• ketones in urine should usually be negative
• ketones

  • positive
  • diabetes
  • dieters - low carb diets
  • severe vomiting, diarrhea
  • small children - small amounts if very active
• ketones

  • interferences - false negatives in improperly preserved specimens
  • acetest tablets - only pick up acetone and acetoaacetic acid (not beta hydroxylacetic acid)
• interferences for leukocyte pad

  • interferences - false negative occur in present of increased glucose/protein levels
  • positives must be confirmed with microscopic examination
• hemoglobinuria

  • in the case of intravascular hemolysis, hemoglobin not bound to haptoglobin will be filtered through glomerulus, gets in filtrate, not reabsorbed
• hemoglobinuria may occur in large intravascular hemolysis when there's not enough haptoglobin
• interferences with blood reagent pad

  • false positives with bacterial enzymes - as some have increased peroxidase
• interferences in blood reagent pad

  • false negatives occur with increased ascorbic acid, protein, and nitrite
• interferences - bilirubin

  • false negatives in urine if not fresh, as bilirubin breaks down in light
  • false positives occur in some pigmented urines
• urobilinogen

  • clinical significance - helps with early detection of liver disease and hemolytic disorders
• urobilinogen

  • reagent strip - Ehrlich's reagent (p-dimethylaminobenzaldenhyde)
  • positive is tan to orange
• urobilinogen - interferences

  • false negative from increased nitrite
  • false positive from Ehrlich reactive chemicals (porphobilinogen [precursor to urobilinogen], indican, and sulfonamides)
• nitrite macroscopic analysis

  • bacteria require contact time in bladder to reduce nitrate to nitrite
  • first morning void is prefered, as bacteria and urine sit in bladder all night and more likely to be detected in dipstick
• RBCs in urine are seen in

  • glomerulonephritis, malignancies, menstruation, trauma