Skip to content
SearchProgress
Display

Display

Theme
Density
Text size

Sign in

Add your earlier progress to your account?

Study progress is waiting to be saved

Cellular casts and renal patterns

17 min

  • Interpret an RBC cast as evidence of bleeding within the nephron
  • Distinguish the renal evidence of a WBC cast from free urinary leukocytes
  • Place renal injury in glomerulus or tubule from protein, heme, cells, and casts together

Read the full reference

Try first

Try first

A fresh voided urine shows many red cells and two structures in which red cells are packed inside a matrix with parallel sides. The requisition notes that the patient is menstruating. What do the two structures mean?

The next section explains it.

Right. The next section explains why.

The next section explains it.

The next section explains it.

Get the idea

Red cell casts put the bleeding in the nephron

A red cell cast holds red cells inside a defined matrix. The cells entered the tubule upstream of where the cast set, most often through an injured glomerulus. A red cell cast is the strongest urine evidence of bleeding within the nephron, especially a glomerular process.1,2 Free red cells from the bladder or from menstrual blood cannot produce one. A loose clump of red cells without an outline is reported as red cells.1 Red cell casts are fragile, so they are sought at low power in a fresh specimen, often with phase contrast.1,3

White cell casts put inflammation in the kidney

A white cell cast holds leukocytes inside a matrix. It places the inflammation in the kidney, which free white cells alone cannot do. Pyelonephritis, interstitial nephritis and glomerular disease all produce white cell casts.1,2 The cast does not name bacteria as the cause. Culture and the other findings do that. Lobed nuclei mark neutrophils. Cells with one round nucleus inside a cast suggest renal tubular cells, and phase contrast or a stain settles it.1

Read the whole urinalysis

Protein, heme, cells, casts and concentration together place the injury. One finding alone does not.1,2

SiteSupporting pattern
Glomerular inflammationHematuria, acanthocytes or dysmorphic red cells, red cell casts, variable protein
Glomerular permeabilityMarked proteinuria, oval fat bodies, fatty casts
Acute tubular injuryRenal tubular cells and their casts, muddy brown granular casts, mild protein, poor concentration
Tubulointerstitial inflammationPyuria, white cell casts, mild protein, microscopic hematuria
Lower urinary tractPyuria, bacteria, hematuria, no renal casts

The laboratory reports the findings. The cause behind a pattern is found through further testing and the clinical evaluation.2

References
  1. Kouri TT, Hofmann W, Falbo R, et al. The EFLM European urinalysis guideline 2023. Clin Chem Lab Med. 2024;62(9):1653-1786. doi:10.1515/cclm-2024-0070
  2. Cavanaugh C, Perazella MA. Urine sediment examination in the diagnosis and management of kidney disease: Core Curriculum 2019. Am J Kidney Dis. 2019;73(2):258-272. doi:10.1053/j.ajkd.2018.07.012
  3. Strasinger SK, Di Lorenzo MS. Urinalysis and Body Fluids. 7th ed. F.A. Davis; 2021. ISBN 978-0-8036-7582-7. F.A. Davis catalog record.

Watch one

A fresh clean-catch urine comes from a 24-year-old man with dark urine two weeks after a sore throat. The report shows:

  • Strip: specific gravity 1.020, protein 2+, blood 3+, leukocyte esterase trace.
  • Sediment: red cells 20 to 50/HPF, many of them acanthocytes, and red cell casts 0 to 2/LPF.
  • Also: white cells 5 to 10/HPF, no white cell casts, rare squamous cells.

Where does the pattern place the injury?

  1. Check the specimen: it is fresh, and rare squamous cells point to a good collection.

    A pattern is only worth reading on a specimen that reflects the patient.

  2. Read the chemistry: protein 2+ with blood 3+.

    Protein and heme together raise the question of a renal source.

  3. Read the red cells: many acanthocytes among 20 to 50 per field.

    Acanthocytes support glomerular bleeding, and the red cell morphology is read from a fresh specimen.

  4. Read the casts: red cell casts are present.

    A red cell cast places the bleeding inside the nephron.

  5. Weigh the rest: white cells are mildly raised, with no white cell casts.

    A few white cells can accompany glomerular inflammation, and white cell casts would point elsewhere.

The protein, acanthocytes and red cell casts together fit glomerular inflammation. Report the findings, and the cause is left to further testing.

Your turn

Problem 1 of 3

Hematuria with dysmorphic RBCs, RBC casts, and proteinuria most strongly supports which anatomic pattern?

Incorrect. Lower-tract inflammation lacks a renal cast pattern. RBC casts and dysmorphic RBCs place the bleeding in the kidney, particularly the glomerulus.

Correct. Dysmorphic RBCs and RBC casts place the bleeding in the glomerulus. Complement, disease-directed serology, and biopsy identify the cause.

Incorrect. Tubulointerstitial inflammation shows pyuria and white blood cell casts. RBC casts and dysmorphic RBCs point to the glomerulus.

Hint
  1. Ask which of the findings could only come from inside the kidney.
  2. Dysmorphic red cells and red cell casts point to the same part of the nephron.

Review Urine patterns and anatomic localization

Problem 2 of 3

Point to the cast that is the strongest evidence of bleeding within the nephron.

Four unlabeled urine sediment photomicrographs in two rows of two.
  1. Top left
  2. Top right
  3. Bottom left
  4. Bottom right
Hint
  1. Look inside each cast at what it holds.
  2. Small, even, round cells without nuclei are red cells.
Show the answer

Red cell cast

The red cell cast holds red cells packed inside a matrix, which places the bleeding in the nephron. The tubular cell cast points to tubular injury, and hyaline and granular casts carry no red cells.

Review Casts

Problem 3 of 3

A fresh urine shows many white cells, several casts packed with neutrophils, bacteria and a positive nitrite. The culture is pending. What does the white cell cast establish?

Casts form only inside the renal tubule. A white cell cast places the inflammation in the kidney.

Contamination adds squamous cells and organisms. It cannot put white cells inside a cast.

Interstitial nephritis and glomerular disease also produce white cell casts. The culture and the other findings identify the cause.

Called a WBC cast specific for bacterial pyelonephritis

A WBC cast places inflammation in the kidney. Pyelonephritis, interstitial nephritis, and glomerular disease all produce it. The cast does not show that bacteria caused it. Culture and the other urine findings identify the cause.

The cast places the white cells inside the tubule. The bacteria and nitrite make infection likely, and the culture confirms it.

Review White blood cells

Use it

  • Tobias Wexley-Hunt, 63, is in the intensive care unit after a long operation with low blood pressure.
  • His creatinine rose from 1.0 to 2.6 mg/dL in 48 hours.
  • A catheter urine is examined 30 minutes after collection.
  • Strip: specific gravity 1.010, protein 1+, blood 1+, leukocyte esterase negative.
  • Sediment: many muddy brown granular casts and renal tubular cells.
  • Several casts hold round cells, each with one round nucleus.
  • Red cells 3 to 5/HPF, about 1 in 20 an acanthocyte, plus one loose cluster of red cells with no outline.
Decision 1 of 3

How do you report the casts that hold round cells with one round nucleus?

Neutrophils have lobed nuclei, and the leukocyte esterase is negative. A single round nucleus fits renal tubular cells.

One round nucleus, free tubular cells in the same field and a negative esterase all fit tubular cells inside the matrix.

Red cells have no nucleus. These cells each have one.

Review White blood cells

Decision 2 of 3

How do you report the loose cluster of red cells?

The cluster has no matrix and no outline around it. Its cells are counted with the other red cells.

A cast needs a continuous matrix with parallel sides. Red cells lying close together without one form a clump.

The red cells are real findings and are counted. The report describes what was seen, and the source is read from the whole pattern.

Review Casts

Decision 3 of 3

Which pattern do the findings fit?

A few acanthocytes among 3 to 5 red cells per field are one finding. With no red cell casts and only 1+ protein, the rest of the urinalysis points elsewhere.

Localized renal injury from one isolated sediment finding

Renal localization rests on a combined pattern of protein, heme, cells, casts, and concentration. Placing injury in the glomerulus or tubule from one finding, such as a few dysmorphic RBCs, reports a localization the rest of the urinalysis may contradict.

That pattern brings pyuria and white cell casts. The cellular casts here hold tubular cells, and the esterase is negative.

The lower tract cannot make casts, and this sediment is full of them.

Muddy brown granular casts, tubular cells and their casts, mild protein and a specific gravity of 1.010 in a man with a rising creatinine form the tubular pattern.

Review Urine patterns and anatomic localization

The clue that settled this case is the tubular cells inside casts, together with the muddy brown granular casts. A handful of acanthocytes could not outweigh them. The report names each finding as it is, and the pattern fits acute tubular injury.

Keep

Sources checked