Microscopic exam of urine pt 2 Flashcards
Where are casts formed?
Only in the nephron (PCT, Loop of Henle, DCT, collecting duct)
Structure of cast
- Parallel sides
- Rounded ends
- Some fragmented
Cast composition
Tamm-Horsfall protein
- glycoprotein constantly excreted by RTE cells for lubrication
- Forms gel matrix of protein
Is Tamm-Horsfall protein detected by reagent strip
Nope! Even though it’s a protein, NOT detected
List steps of cast formation
- Tamm-Horsfall aggregates to RTE cells to form protein fibrils
- Fibrils form loose network such that components in urine can get trapped
- Further interweaving of fibrils to form solid matrix
- Urine components attach to matrix
- Cast detaches from RTE and exits nephron
Cylinduria
Casts in urine
Cast formation occurs more readily if:
- Decreased urine flow (stasis)
- Acidic pH bc casts dissolve in alkaline pH
- Increased electrolytes
T/F
Cast formation can block urine flow within nephron
True
Non-pathological causes of casts
Exercise and dehydration
Pathological causes of casts
Renal conditions
List the types of casts
- Hyaline
- Cellular (RBC, WBC, RTE)
- Fatty
- Granular (fine or coarse)
- Broad
- Waxy
Hyaline cast normal value
0-2/hpf
Which cast is most frequently seen?
Hyaline cast
Non-pathological causes of hyaline casts (hint: there’s 3)
- Strenuous exercise
- Dehydration
- Heat exposure
Pathological causes of hyaline casts (hint: there’s 4)
- Acute glomerulonephritis
- Pyelonephritis
- Chronic renal disease
- Congestive heart failure
How to visualize hyaline casts?
- Decreased light bc refractive index similar to urine
- Sternheimer-Malbin stain or phase microscopy
RBC casts
- RBCs imbedded inside the matrix, NOT stuck outside
- Must distinguish from clump of RBCs
- Typically see free-floating RBCs
Chemical strip test result if RBC casts are present
Blood = positive
Non-pathological cause of RBC casts
Strenuous exercise (rare)
Pathological cause of RBC casts
- Indicates nephron bleeding
- May see proteinuria
- Associated with glomerulonephritis
ID element and medical state
- RBC cast
- Hemoglobinuria (orange-red or red-brown)
ID element and medical state
- RBC cast
- Methemoglobinuria (brownish)
ID the element
- WBC cast with WBCs imbedded in the matrix (don’t confuse with WBC clumps)
- PMNs, granular appearance
Pathological causes of WBC casts
- Pyelonephritis (upper UTI), presence of bacteria may be significant
- Acute interstitial nephritis (absence of bacteria, may see eosinophils)
- Glomerulonephritis
WBC casts associated with __
Infection or nephron inflammation
T/F
Cystitis of lower UTI produces WBC casts
False, it does not
Bacterial casts
- Bacteria inside the cast, not attached outside of a hyaline cast
- WBC and free-floating bacteria present
- Hard to ID, confused with granular casts
- Rare
- Confirm with Gram stain
Bacterial casts associated with
Pyelonephritis
ID the element
Bacterial cast
RTE cast
- Seriously pathological but rare
- Caused by tubular destruction
- Must distinguish from WBC cast (use staining and mononuclear structure)
ID the elements
Fatty/oval fat body cast
- Composed of fat droplets or oval fat bodies
- Fat appears refractile
- Confirm with polarized light and fat stain (will not stain with Sternheimer-Malbin)
Pathological causes of fatty/oval fat body casts
- Nephrotic syndrome
- Tubular necrosis
- Crush injuries
ID the element
FATTY CAST
ID the element
Mixed cellular cast (RBCs and WBCs)
How to ID mixed cell casts
Use staining
Common mixed cellular cast mixtures and their disease associations
- RBC + WBC = glomerulonephritis
- WBC + RTE = pyelonephritis
Granular casts
These casts pick up materials from urine, which start to degrade and form granularity (crystals, RBC, WBC, cellular material from RTE is most common)
What are the two ways that granular casts can form?
- Free cells in tubular lumen are destroyed and incorporated as cast forms
- Cellular cast forms first and the cells get destroyed inside the already-formed cast
T/F
Granular cast starts as coarse and becomes fine over time as granules disintegrate
True
What is required for a granular cast to form?
Urinary stasis (can’t pee)
ID the element
Fine granular cast
ID the element
Coarse granular cast
ID the element
Coarse granular cast
Waxy cast
- Occur from long-term urinary stasis
- Occur from the further breakdown of granules contained within granular casts, also associated with destruction of hyaline matrix
Waxy casts associated with
Chronic renal failure
Waxy casts usually seen ___
Along with other casts
ID the element
Waxy cast
ID the element
Waxy cast
ID the element
Waxy cast
How to distinguish between hyaline and waxy casts?
- Waxy cast = broken/brittle ends
- Hyaline casts = intact, rounded ends
Distinguish the elements
Broad casts
- Frequently referred to as renal failure casts bc cell death leads to wider casts
- 2-6x wider than the typical casts and usually occur from very long-term urinary stasis
- Can form from any type of cast
Broad casts formed from ___
- Any type of cast
- Most common are granular or waxy type
Two ways to form broad casts
- From DCT due to dilation or tubular wall destruction (get wider)
- Collecting ducts (wider than DCT) due to severe decrease in renal flow
ID the element
Broad granular cast
ID the element
Broad waxy cast
ID the element
Broad casts
