Casts are cylindrical particles found in urine that are formed in the kidney's distal convoluted tubules and collecting duct. They are composed of Tamm-Horsfall protein and other substances filtered from the blood. Casts come in various shapes and sizes depending on the tubule diameter and can be acellular (containing only protein) or cellular (containing cells and debris). The presence of casts provides information about kidney function and diseases, with hyaline casts being most common and fatty, red blood cell, or white blood cell casts indicating more serious conditions such as infection or kidney failure.

1. Casts In
Urine
Reem Sawalha

2. Overview
● Casts
● Casts Formation
● Kind of casts

3. Casts
Casts are microscopic cylindrical particles that can
be seen in urine under microscope during urinalysis .
And their presence in urine is called cylindruria .
They are the only elements found in the urinary
sediment that are unique to the kidney as they are
formed in the distal convoluted tubules (DCT) or the
collecting duct .

4. Because casts are formed within the tubules , they are
tiny tube - shaped with parallel sides , somewhat
rounded ends
and they may contain additional elements present in
the filtrate .

5. Note
Examination of the sediment for the detection of
casts is performed using low power magnification
(10x ) . Low-power scanning should be performed
along the edges of the cover slip .

6. Casts Formation :
They are formed in the Distal convoluted tubules and the
collecting duct with a core matrix of Uromodulin , other proteins
like albumin and immunoglobulins also incorporate
into the cast matrix .

7. Uromodulin forms fibrils that attach it to the lumen
cells , holding it temporarily in place while it enmeshes
into its matrix many substances that may be present .
after that detachment of protein fibrils from tubular
epithelial cells and excretion of the cast .

8. Uromodulin
Also known as Tamm - Horsfall protein (THP) .
It’s a glycoprotein that is secreted by the renal
tubular cells of the thick ascending limb of the loop
of Henle and by the distal convoluted tubules .

9. It’s normally found in urine and plays a role in
regulating salt transport and protect against
urinary tract infection and kidney stones, and
have roles in kidney injury and innate immunity .
it’s excreted at a relatively constant rate , but the
rate of excretion appears to increase under
conditions of stress and exercise

10. Factors of casts formation :
● Urine stasis (low flow )
● Acid PH
● Increased solute concentration
● Increased plasma proteins ( Albumin ,
Hemoglobin , Myoglobin )

11. shapes and sizes
The shape and size of urinary casts can vary
greatly depending on the diameter and shape of
the tubule in which they are formed .
casts can be short and stubby or thin or straight ,
curved or convoluted .

12. Sometimes casts are well formed at one end but are
tapered or have a tail at the other end , these casts are
called cylindroids .

14. classifications
Casts are classified based on the composition
of their matrix and the types of substances or
cells enmeshed in them .
Casts are classified into Acellular and Cellular
casts .

15. Acellular Casts :
● Hyaline Casts
Most common type of casts . They are only
solidified Tamm-Horsfall mucoprotein so they are
clear . The presence of 0-2 hyaline casts / Lpf is
considered normal .

16. These numbers increase physiologically in normal
individuals in dehydration or vigorous exercise or
after heat exposure .
And increases pathologically in renal disease and
congestive heart failure

18. ● Granular Casts
Second most common type of casts .Can result from
the breakdown of cellular casts . and when
granular casts remain in the tubules for extended
periods, the granules further disintegrate, giving the
cast matrix a waxy appearance .
It’s an indicative of chronic renal disease and of
acute tubular necrosis .

21. ● Waxy Casts
indicates very low urine flow , prolonged stasis and
tubular obstruction . It’s associated with Kidney
Failure .
They represent an advanced stage of other casts (
Hyaline , Granular , Cellular )
Found most frequently in patients with chronic
renal failure , so they are referred to as renal failure

23. ● Fatty casts
Seen in conjunction with oval fat bodies and free
fat droplets in disorders causing lipiduria .
mostly frequently associated with nephrotic
syndrome but also seen in toxic tubular necrosis ,
diabetes mellitus .
can be confirmed using sudan III or Oil Red O fat
stains

25. Cellular Casts
● Red Blood Cells Casts
All RBCs casts are considered pathogenic and it
indicates a bleeding within the nephron , it’s
also an indicative of granulomatosis with
polyangiitis , systemic lupus erythematosus .
it’s associated with dysmorphic erythrocytes

27. ● White Blood Cells Casts
It signifies infection or inflammation within the
nephron . and strongly suggests pyelonephritis .
Observation of free WBCs in the sediment is also
essential .

29. ● Bacterial Casts
should be in association with loose bacteria , WBCs ,
and WBCs casts . Seen in pyelonephritis .
Could be mistaken with Granular casts .
confirmation is done by performing a Gram stain .

31. ● Epithelial Cell Casts
Formed by inclusion of epithelial cells of the
tubule lining . can be seen in acute tubular
necrosis , toxic ingestion such as mercury .
may be seen in people with cytomegalovirus ,
Hepatitis .

33. ● Mixed Cellular casts
Casts containing multiple cell type like RBCs , WBCs
and RTE casts .
● Broad Casts
All types of casts may occur in the broad form .
It’s often referred to as renal failure casts .

35. References :
- https://en.wikipedia.org/wiki/Urinary_cast
- https://en.wikipedia.org/wiki/Uromodulin
- https://www.nature.com/articles/nrneph.2017.101
- https://laboratoryinfo.com/types-of-casts-in-urine-and-their-clinical-signifi
cance/
- Fundamentals of Urine & Body Fluid Analysis, 3th Edition By Nancy
A.Brunzel
- Urinalysis and Body Fluids , 6th Edition By Susan King Strasinger &
Marjorie Schaub Di Lorenzo