Urinalysis

Snapshot

• A 22-year-old woman presents with dysuria, pyuria, and increased urinary frequency. She reports her symptoms began approximately 2 days prior to presentation. She has had similar symptoms 5 months ago. She is sexually active and uses condoms inconsistently. Physical examination is unremarkable. Urinalysis is positive for pyuria and bacteruria. Urine culture demonstrates ≥ 100,000 colony forming units (CFU) /mL. (Urinary tract infection)

Introduction

• Process
  • a fresh urine specimen is obtained and subsequently centrifuged
    • the supernatant is placed in a separate tube
      • a urine dipstick is placed in the supernatant to analyze for
        • pH
          • normal is between 5-6.5
          • clinical correlate
            • urine pH >7.5 can suggest a urinary tract infection (UTI) secondary to urea-splitting microbe
        • glucose
          • clinical correlate
            • urine glucose can be detected in the urine in poorly controlled diabetes mellitus
        • ketones
          • clinical correlate
            • urine ketones can be seen in poorly controlled diabetes mellitus
        • nitrite
          • clinical correlate
            • can be a reasonably good screening test for UTI
        • heme
          • clinical correlate
            • typically indicative of blood in the urine
              • however, the urine can be heme positive in the setting of intravascular hemolysis and rhabdomyolysis
        • protein
          • clinical correlate
            • elevated protein in the urine can suggest a nephrotic syndrome
      • specific gravity
        • reflects the weight of a solution compared to the weight of distilled water
          • the solution and distilled water must be of equal volume
          • when the urine contains large solutes (e.g., glucose) the specific gravity increases
      • urine osmolality
        • measures the amount of dissolved particles per unit of water found in urine
    • the sediment should be resuspended and then transferred to a slide for analysis
      • urine casts
        • these represent protein and cell precipitates generated within the tubular lumen
      • red blood cells (RBCs)
        • red cell morphology
          • dysmorphic RBCs
            • suggests glomerular bleeding
          • round and uniform RBCs
            • suggests extrarenal bleeding (e.g., ureter and bladder)
      • white blood cells (WBCs)
        • seeing WBCs in the urine is termed pyuria and suggests an infection or inflammatory process in the urinary tract
        • neutrophils are more commonly seen
          • eosinophiluria can be see in drug-induced acute intestitial nephritis
      • epithelial cells
      • crystals