Pathophysiology
P-II-10. Kidney disease, Case 2
腰疾患 症例2
Complaints:
- 64-year-old man at the GP
- Frequent urination (every ½–1 hour)
- Thin urine stream
- Urgent urination
- Urination during the night (nocturia)
- Alternating abdominal pain
- Red urine
- Pain above the pubic bone
Additional notes: family members said he often goes to the toilet; urination is sometimes painful; urine is sometimes dark; he has to get up at dawn.
Laboratory (blood):
- Sodium (Na⁺): 139 mmol/L
- Potassium (K⁺): 4.2 mmol/L
- Urea: 4.1 mmol/L
- Creatinine: 90 μmol/L
- Glucose: 5.3 mmol/L
- eGFR (CKD-EPI): 80 mL/min/1.73m²
Laboratory (urine) — chemistry test strip:
- Bilirubin: neg
- Urobilinogen: 0.2 mg/dL
- Ketone: neg
- Vitamin C: neg
- Glucose: neg
- Protein: 30 mg/dL
- RBC: 35 RBCs/uL
- pH: 5.5
- Nitrite: neg
- White blood cell (LEU): neg
- Specific gravity: 1.025
- Turbidity: turbid
- Colour: red
Urine sediment:
- Red blood cell (RBC): 22.4 /uL
- White blood cell (WBC): 2.5 /uL
- Crystal: 14.7
- Calcium oxalate monohydrate: 1.6
- CaOx dihydrate: 12.4
- Hyaline cast: 0
- Pathologic cast: 0
- Non-epithelial cell: 2
- Epithelial cell: 8
- Bacterium: 3
- Mucus: 71.4
Key Quotes & What They Tell Us
| Quote / Value | Interpretation |
|---|---|
| “Crystal: 14.7”; CaOx monohydrate 1.6 + dihydrate 12.4 | Abundant calcium-oxalate crystals → calcium-oxalate urolithiasis (stone disease) |
| “Red urine”; urine RBC 35/µL (strip), sediment RBC 22.4/µL | Haematuria from stone-induced mucosal trauma in the urinary tract |
| Nitrite negative; WBC negative; bacteria only 3 | No infection → the haematuria/crystalluria is not from a UTI |
| “Frequent urination … thin urine stream … nocturia … urgency” | Lower urinary tract / obstructive voiding symptoms (e.g., a bladder stone or prostatic enlargement in a 64-year-old man) |
| “Pain above the pubic bone”; “alternating abdominal pain” | Suprapubic/colicky pain consistent with stones in the bladder or ureter |
| Creatinine 90 µmol/L; eGFR 80; urea 4.1 | Renal function still preserved — no significant obstructive nephropathy yet |
Key Points
- Diagnosis: Urolithiasis — calcium-oxalate urinary stones — with haematuria and obstructive lower-urinary-tract symptoms.
- Crystal type: Calcium oxalate (monohydrate + dihydrate), the commonest stone composition.
- No infection: Negative nitrite/leukocytes and scant bacteria distinguish this from a UTI.
- Pathophysiology: Supersaturation of urine → crystal aggregation → stone formation → mucosal injury (haematuria) and outflow symptoms.
- Renal function: Preserved, indicating no current high-grade obstruction.
- Context: In a 64-year-old man, voiding symptoms also raise the possibility of co-existing prostatic enlargement/bladder stone.
一問一答
▶What is the diagnosis in a patient with red urine, abundant calcium-oxalate crystals, and colicky suprapubic pain?
Urolithiasis (calcium-oxalate urinary stones).
▶What is the most common composition of urinary stones, seen in this patient?
Calcium oxalate (monohydrate and dihydrate).
▶Why does this patient have haematuria?
Stones and crystals cause mechanical trauma to the urinary tract mucosa, leading to bleeding.
▶Why is a UTI excluded as the cause of haematuria in this case?
Negative nitrite, negative leukocytes, and only scant bacteria argue against urinary infection.
▶What is the pathophysiology of urinary stone formation?
Supersaturation of urine with stone-forming salts → crystal nucleation and aggregation → stone growth.
▶Why does the patient have obstructive voiding symptoms (frequency, weak stream, nocturia, urgency)?
Lower urinary tract obstruction — e.g., a bladder stone and/or prostatic enlargement in a 64-year-old man.
▶Why is renal function (creatinine 90, eGFR 80) still preserved in this patient?
There is no current high-grade obstruction causing obstructive nephropathy.
▶What does suprapubic and colicky abdominal pain suggest about stone location?
Stones in the bladder or ureter, producing suprapubic and colicky pain.
▶Why is the urine turbid and red in this patient?
Red colour from haematuria and turbidity from crystals/cells in the urine.
▶Why might a 64-year-old man's voiding symptoms also raise suspicion of prostatic enlargement?
Benign prostatic hyperplasia is common at this age and causes obstructive lower urinary tract symptoms.
▶Why does dehydration/low urine volume promote stone formation?
Concentrated urine raises the concentration of stone-forming salts above their solubility, favouring crystallization.
▶What does the mild proteinuria (30 mg/dL) most likely reflect here?
Minor leakage associated with haematuria/mucosal irritation rather than significant glomerular disease.
▶What is renal/ureteric colic?
Severe, waves of flank/abdominal pain caused by a stone obstructing and stretching the ureter.
▶How can acidic urine (pH 5.5) favour certain stones?
Low urine pH promotes uric-acid and calcium-oxalate stone formation.
▶What lifestyle measure best prevents recurrent calcium-oxalate stones?
Increased fluid intake to keep urine dilute (plus dietary modification).
▶Why does the sediment show many crystals but no casts?
Crystalluria reflects stone disease, while the absence of casts indicates no significant glomerular/tubular parenchymal disease.
▶What imaging is typically used to confirm and locate urinary stones?
Non-contrast CT (or ultrasound) of the urinary tract.
▶Why can a bladder stone cause an intermittent/thin urine stream?
A stone can intermittently obstruct the bladder outlet, interrupting and weakening flow.
▶What serious complication arises if a urinary stone causes high-grade obstruction with infection?
Obstructive pyelonephritis/urosepsis and acute kidney injury — a urological emergency.
▶Why does normal glucose and negative urine glucose help exclude diabetes here?
Blood glucose is normal (5.3 mmol/L) and there is no glucosuria, so diabetes is not contributing to the stones/symptoms.