Urinalysis: centrifuge sediment

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Overview

  • White and red blood cells, casts, crystals, bacteria and neoplastic cells can be seen on microscopic examination in certain diseases of the urinary tract, eg urinary tract infection, urolithiasis, acute renal failure, transitional cell carcinoma, prostatic disease, crystalluria.
  • Sediment examination is an essential part of urinalysis.

Result data

Normal (reference) values



Hematuria
  • Cystocentesis: 0-3 RBCs/high power field.
  • Catheterization: 0-5 RBCs/high power field.
  • Free flow sample: 0-7 RBCs/high power field.
White blood cells (WBCs)
  • Cystocentesis: 0-3 WBCs/high power field.
  • Catheterization: 0-5 WBCs/high power field.
  • Free flow sample: 0-7 WBCs/high power field.
Bacteria
  • Negative in cystocentesis sample.
  • In other samples may be the result of contamination.
Casts
  • 0-2 hyaline casts/high power field.
  • 0-1 granular casts/high power field.
Crystals
  • May normally have struvite , calcium oxalate , bilirubin crystals in small numbers. (Figs. 1-4)
  • Urinalysis cysteine crystalFig.5 Urinalysis cysteine crystal
    Other less common crystals may be normal (Fig. 5).
  • Dalmatians may normally have uric acid and ammonium urate crystals. (Figs. 6-7)

Abnormal values

Hematuria

Urinary tract infection [Cystitis] is the most common cause, therefore urine culture [Urinalysis: bacteriology] is indicated even if no evidence of pyuria or bacteriuria is found.

Nitrituria Pyuria Bacteriuria
  • Urinary tract infections.
Casts
  • Hyaline casts: associated with proteinuria.
  • Epithelial, fatty , granular and waxy casts: associated with conditions causing degeneration and necrosis of tubular epithelial cells, eg dehydration, nephrotoxins, tubular hypoxia, acute oliguric renal failure.
  • Red blood cell casts: hemorrhage into renal tubules or severe glomerular inflammation.
  • White blood cell casts: renal inflammation, upper urinary tract infection.
Crystalluria
  • The following may be abnormal:
    • Struvite ( triple phosphate; ammonium-magnesium phosphate).
    • Urinalysis calcium oxalate crystalFig.8 Urinalysis calcium oxalate crystal
      Calcium oxalate (Fig. 8).
    • Calcium phosphate.
    • Urinalysis urate crystalsFig.9 Urinalysis urate crystals
      Ammonium urate (Fig. 9).
    • Bilirubin.

    May be normal or abnormal; use caution in interpretation.
  • Calcium oxalate monohydrate crystals (may be present with ethylene glycol toxicity). Absence does not rule out toxicity.
  • Tyrosine crystals (liver disease), sulfomamide crystals and cysteine crystals (enzyme deficiency).

Errors and Artifacts

  • Not using fresh urine.
  • Incorrect storage.
  • Centrifuge speed >5000 rpm.
  • Shaking sample.
  • Using a collection technique other than cystocentesis.
  • Not being consistent in analysis.
  • Alkaline urine.
  • Dilute urine.
  • Exposure to room temperature for hours (results in lysis of WBCs).

Hematuria

  • Increase:
    • Trauma during sampling.
    • Contamination with vaginal/preputial secretion.
  • Decrease:
    • Due to hemolysis.
    • Hyposthenuric urine.
    • Very acid urine.
    • Very alkaline urine.

Pyuria

  • Increase on dipstick:
  • Increase:
    • Contamination (preputial/vaginal secretions)
  • Decrease on sediment:
    • Alkaline urine
    • Dilute urine
    • Exposure to room temperature for hours (results in lysis of WBCs).

Bacteria

  • Increase:
    • Urine at room temperature > 2 hrs.
    • Contamination of equipment and stains.
  • Decrease:
    • Recent antibiotic therapy.
    • Diuresis.

Casts

  • Decrease:
    • Vigourous handling.
    • Centrifuge >5000 rpm.
    • Sample allowed to stand for hours.
    • Alkaline urine.

Crystals

  • Sulphonamide crystals.
  • The formation of crystals depends on pH.
  • An alteration of pH will alter the crystal content of the sample.
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