Urinalysis Flashcards
How is a urine sample collected and when must it be examined? Why?
Clean-catch midstream
- within an hour of voiding, so that casts and red blood cells can be seen before they deteriorate -> otherwise must refrigerate
What are the three components of the routine urinalysis?
- Examination of urine physical characteristics
- Chemical analysis with urine dipstick
- Microscopic examination of urine sediment
Normal urine is clear with a clear-to-yellow color. What pathologies are each of the following urines associated with?
- Hazy urine
- Smoky urine
- Foamy urine
- Hazy urine - presence of cells or crystals in urine
- Smoky urine - slight macrohematuria, often seen in acute glomerulonephritis
- Foamy urine - proteinuric states (as in the top of an eggwhite).
What is the definition of specific gravity? What is it an indicator of?
specific gravity = weight of urine / weight of same volume of distilled water
Indicator of concentration of dissolved particles in urine (dependent on weight and number of particles)
What are states which will create low or high urine specific gravity?
Low - excess fluid intake, diabetes insipidus
High - dehydration, HMW substances in urine (glucose, radiographic dye)
What is urine osmolality used for / when might it be better?
Tests the number of particles dissolved in urine per kg of water
- > useful when high molecular weight particles like glucose are obscuring the true concentrating power of the kidneys
- > not dependent on MW
Why is urine osmolality not always used to measure the kidney concentrating ability?
Despite always being more accurate, it is technically more demanding and needs to be ordered separately
How are albumin and smaller proteins like immunoglobulin light chains handled at the glomerulus and proximal tubule?
Albumin - only a very small amount filtered
Ig light chains / other LMW proteins - extensively filtered
Proximal tubule aids in reabsorption of both of these entities
Should there ever be any protein in the urine normally? Why?
Yes, the thick ascending loop of henle (TALH) SECRETES Tamm-Horsfall Protein into the urine, which accounts for better than 50% of the daily 40-80mg of protein excreted.
What is the definition of abnormal proteinuria and what can urine dipstick detect?
> 150 mg/day in urine
Dipstick can detect >250 mg/day.
Not sensitive for lower proteinuria
Will glomerular or tubular disorders typically cause more severe proteinuria?
Tubular - 1+ or 2+ protein from failed reabsorption
Glomerular - far worse, 3+ or 4+ protein
What type of protein is the urine dipstick best at detecting, and because of this, what can we not rule out if we have a negative proteinuria test but a patient has severe back pain on presentation?
Best at detecting albumin in urine
Cannot as easily detect Bence-Jones proteins (Ig light chains) or Tamm-Horsfall.
Negative dipstick does rule out multiple myeloma -> requires urine electrophoresis
What does the urine dipstick detect to pick up on RBCs in the urine?
Intact RBCs, free hemoglobin, myoglobin
If urine dipstick is positive for blood, but no intact RBCs can be seen on examination of urine sediment, what two diagnoses should you be entertaining?
Rhabdomyolysis - myoglobinuria
Intravascular hemolysis - hemoglobinuria
What is renal glycosuria?
Condition where proximal convoluted tubules cannot reabsorb as much glucose as the average person, so glucose becomes positive in urine even with normal blood sugar levels
What are the usual causes of renal glycosuria?
- Proximal tubule disorders - i.e. Fanconi syndrome
- Interstitial nephritis
- Pregnancy
How is urine sediment examined?
Urine is spun down with centrifuge, supernatant is discarded, and pellet is resuspended in saline.
Sediment is examined under high power field, and the findings per HPF are averaged.
How many RBCs per HPF is normal? What are the two types of RBCs which can be seen and why is this significant?
0-2/ HPF
- Monomorphic - uniform size / shape - could originate anywhere in urinary tract
- Dysmorphic -varying size / shapes - squeezed through capillaries, bleeding from glomerulus highly suggestive of glomerulonephritis
What is a normal urine sediment WBC count, and how can they be told apart from RBCs?
Normal is 0-2/HPF again
Usually they are neutrophils. They will be larger than RBCs, granular, and nuclei can be seen.
How many renal tubular epithelial cells can be seen per HPF? What are the three types?
0-2/HPF again
- Renal tubular epithelial cells
- Transitional epithelial clels
- Squamous epithelial cells
How are renal tubular epithelial cells identified? What condition would cause them to increase?
Slightly larger than WBC with large, round nucleus which is very prominent. They will also be slightly less granular than WBCs.
Elevated in renal tubular injury
How are transitional epithelial cells identified? What condition would cause them to increase?
Round or pear-shaped cells, appear 2-4 times larger than WBCs. They are larger and tend to appear in groups.
Seen in inflammatory conditions of ureters or bladder, as they line the urinary tract from upper urethra to renal pelvis.
How are squamous epithelial cells identified? Why might they be present?
Large cytoplasm sheets with small central nuclei
Usually present due to contamination of sample -> from vagina or urethra (poorly done clean catch)
What urinalysis finding is pathognomonic of nephrotic syndrome and how does it appear under the microscope?
Oval fat body -> renal tubular epithelial cells with fat droplets in their cytoplasm, due to fat secretion through glomerulus
Polarized light shows “Maltese Cross” pattern of cholesterol and cholesterol ester
What is the clinical significance of Tamm-Horsfall protein?
It is a mucoid glycoprotein which tends to aggregate in tubules
-> aggregations are responsible for formation of protein gels -> casts. Things can stick to those casts.
-casts are ALWAYS renal in origin
What are hyaline casts and when do they aggregate?
Acellular, highly transparent casts made of gelled Tamm-Horsfall protein.
Normal finding seen in concentrated urine samples, as in dehydration or exercise.
Can RBC casts be normal, and when are they seen?
Always pathologic
Seen most commonly in glomerulonephritis
Rarely seen in pyelonephritis / renal infarction
When are WBC casts seen?
When the interstitium around the tubules is inflamed. Casts are usually formed by PMNs.
-> interstitial nephritis or pyelonephritis
What are renal epithelial cell casts? When are they seen?
When renal tubular epithelial cells slough off and embed into hyaline casts
-> renal tubular injury, usually acute tubular necrosis
What are the two types of granular casts and which one indicates acute tubular necrosis?
- Finely granular casts - aggregations of proteins and cellular debris, non-specific renal injury
- Coarsely granular casts - “Muddy brown” - very dark colored, indicative of acute tubular necrosis.
How do waxy casts appear and why? What disease process do they indicate?
Appear as “broad” casts which are similar in appearance to hyaline casts, but borders are more determinable
- > may be due to degeneration of granular casts
- > appear “broad” because of dilation or hypertrophy of tubules
Seen in advanced chronic kidney disease / renal failure
What are casts embedded with lipid? What will they show under polarized light?
Fatty casts - seen in nephrotic syndrome with oval fat bodies and free fat droplets
Will show Maltese Cross pattern from cholesterol / cholesterol esters under polarized light
What urine crystals are expected to form at low pH?
Uric acid
Cystine
Calcium oxalate - precipitated by hypocitraturia (associated with low pH)
What crystals are expected to form at high pH (alkaline)?
Calcium carbonate
Ammonium magnesium phosphate (triple phosphate / struvite)
What is one crystal type which is always abnormal if it appears in urine and what does it look like?
Cystine - think Sixtine - Six sides = hexagonal shape
Present in conditions of cystinuria
What causes formation of calcium oxalate crystals usually, and how do they appear?
Ethylene glycol ingestion
Crystals appear “envelope-shaped” -> i think they look like origami game
How do uric acid crystal appear?
Rhomboid or diamond-shaped
-> also appear slightly brown from taking up pigment
How do triple phosphate / struvite / ammonia magnesium phosphate crystals appear? What condition do they appear in?
Coffin lid shaped
Appear in conditions of increased urine pH, especially UTI’s with urease + organisms (urea -> ammonia).
