Urinalysis Flashcards
what is the single best test for the evaluation of renal function
URINALYSIS
urine composition
*a solution, usually sterile, containing:
-water
-phosphorous
-nitrogen
-organic compounds
-cells
when to perform a urinalysis (UA)
*sports physicals
*first complete history & physical
*initial evaluation of hypertension
*any systemic disease with renal involvement
*to evaluate for urinary tract infection
*initial fever in hospitalized patient
urine dipstick checks for
*nitrite (+ means bacteria in urine)
*glucose
*heme pigment
*protein
*leukocyte esterase (+ means WBCs in urine)
*bilirubin
specific gravity of urine
*the ratio of the density of a substance to the density of a standard (usually water)
*measures how concentrated the urine is
water has a specific gravity 1.000
concentrated urine > 1.020
very concentrated > 1.040
urinalysis - heme pigment
*heme pigment is positive in UA in:
-hemolysis
-rhabdomyolysis
-hematuria
urinalysis - protein
*small amount of urinary protein can occur from the tubule (<3 g/day)
*if > 3 g/day, it is nephrotic proteinuria (suggests a GLOMERULAR DISORDER)
casts in urine
*presence of casts indicates that hematuria/pyuria is of glomerular or renal tubular origin
*all casts contain a matrix composed primarily of Tamm-Horsfall mucoprotein (uromodulin), secreted by renal tubular cells to prevent UTIs
*bladder cancer, kidney stones → hematuria, NO casts
*acute cystitis → pyuria, NO casts
RBC casts
*seen in glomerulonephritis, vasculitis, and hypertensive emergency
*seen with other red cells nearby
*NOT seen in bleeding of the lower urinary tract (beyond the kidney itself)
WBC casts
*seen in pyelonephritis, tubulointerstitial inflammation, and transplant rejection
*NOT seen in cystitis
coarse granular casts
*seen in acute tubular necrosis (ATN) [e.g. rhabdomyolysis, sepsis, gentamicin, contrast]
*can be “muddy brown” in appearance
hyaline casts
*made of uromodulin (most common protein in urine)
*nonspecific, can be a NORMAL finding with dehydration, exercise, or diuretic therapy
*more likely to be seen in concentrated urine
renal tubular epithelial cells (RTEs) in urine
*seen in acute tubular necrosis
oval fat bodies (fatty casts)
*fat droplets in degraded tubular cells (lipid-laden cells)
*seen in nephrotic syndrome
*associated with “Maltese cross” sign
calcium oxalate crystals
*a NORMAL finding in acid urine
*can also be seen with calcium oxalate stones
urate crystals
*typically rhomboid shape
*can be seen with uric acid kidney stones
*radiolucent (not seen on X-ray)
triple phosphate crystals
*usually seen in patients with long-standing stones in the bladder
*seen in struvite stones (caused by infection with urease + organisms)
*“coffin lids”
yeast in urine
localizing renal failure: PRE-RENAL
*prior to the glomerulus
*example: volume depletion
*high BUN/Cr ratio
*UA with concentrated urine, hyaline casts:
-urine osmolality: > 500
-urine sodium: < 20
-FEna: < 1%
-serum BUN/Cr ratio: > 20
localizing renal failure: INTRINSIC RENAL-GLOMERULAR
*proteinuria
*frequent hematuria (RBC casts)
*can be tubular (ATN), interstitial (AIN), glomerular, or vasular
*urinalysis:
-urine osmolarity: < 350
-urine sodium: > 40
-FEna: > 2%
-serum BUN/Cr ratio: < 15
localizing renal failure: INTRINISC - ACUTE TUBULAR NECROSIS
*occurs in the interstitium or tubule
*UA:
-at least 1 granular cast per low powered field
-usually 1 renal tubular epithelial cell per high powered field
*example: rhabdomyolysis
localizing renal failure: INTERSTITIAL NEPHRITIS
*eosinophiluria is NOT a diagnostic test and actually unhelpful
*pyuria is also unhelpful
localizing renal failure: POST-RENAL
*example: obstruction
*consider foley or ultrasound
*UA: bland
chronic renal failure - clues
*history of HTN
*history of high serum creatinine
*history of proteinuria
*small kidneys on ultrasound
acute renal failure - clues
*no history of HTN
*active urinary sediment frequently
*MOST LIKELY TO RESPOND TO TREATMENT
*normal sized kidneys on ultrasound
HIV nephropathy - time course & UA
-time course: SLOW
-UA: proteinuria; no RBC
rapidly progressive glomerulonephritis - time course & UA
-time course: FAST
-UA: RBC casts
acute tubular necrosis (ATN) - time course & UA
-time course: FAST
-UA: GRANULAR casts
contrast the time courses & UA results of: HIV nephropathy vs. rapidly progressive glomerulonephritis vs. ATN
*HIV nephropathy:
-time course: slow
-UA: proteinuria; no RBC
*rapidly progressive glomerulonephritis:
-time course: fast
-UA: RBC casts
*ATN (acute tubular necrosis):
-time course: fast
-UA: granular casts
