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