Nephrology
Urinary stones and nephrocalcinosis
Prevention, stone types, hyperoxaluria, nephrocalcinosis, and practical 24-hour urine interpretation.
Urinary stones and nephrocalcinosis
Stone formation is a continuum driven by urinary supersaturation, crystallisation promoters, and inhibitors such as citrate. Urinary calcium is also a continuous risk variable rather than a single safe/unsafe cut-off.
General prevention
- Aim for fluid intake around 2.5–3 L/day when clinically appropriate, producing more than 2.5 L of urine per 24 hours.
- Keep normal dietary calcium around 1–1.2 g/day, reduce sodium chloride to about 4–5 g/day, and individualise animal protein.
- Do not routinely restrict dietary calcium in calcium-oxalate stone formers; calcium with meals binds oxalate in the gut. It can be particularly useful with enteric hyperoxaluria.
- High sodium, excess animal protein, and high-dose vitamin C can worsen risk in selected patients.
Stone types and medicines
Uric-acid stones are strongly influenced by low urine pH; alkaline citrate is the main treatment, with a monitored pH around 7.0–7.2 when dissolution is intended. Hyperoxaluria may be dietary, enteric, or primary. Struvite stones are linked to urease-producing bacteria and usually require stone removal plus treatment of persistent bacteriuria. Cystinuria requires very high fluid output and urine alkalinisation. Loop diuretics, triamterene, indinavir, carbonic-anhydrase inhibitors, and some antibiotics can alter stone risk or cause crystalluria.
Nephrocalcinosis
Nephrocalcinosis means calcium-phosphate or calcium-oxalate deposits in kidney tissue. Causes include hyperparathyroidism, primary or enteric hyperoxaluria, distal renal tubular acidosis, medullary sponge kidney, vitamin-D disorders, sarcoidosis, idiopathic hypercalciuria, hypocitraturia, Dent disease, and Bartter syndrome. Evaluation is cause-specific and may include calcium/PTH, vitamin D, electrolytes, bicarbonate, urine pH and a detailed 24-hour urine collection.
Practical 24-hour urine targets
| Variable | Practical interpretation |
|---|---|
| Urine volume | Preventive target >2.5 L/24 h. |
| Creatinine | Collection completeness: women 15–20 mg/kg/day; men 18–25 mg/kg/day. |
| pH | <5.5 is very acidic; persistently high values may suggest distal RTA or infection after the clinical context is checked. |
| Oxalate | >0.40 mmol/day suggests hyperoxaluria; >0.5 suggests enteric disease; >1 strongly suggests primary hyperoxaluria. |
| Citrate | Hypocitraturia is commonly considered below 1.7 mmol/day in men or 1.9 mmol/day in women. |
The supplied Word document contains the expanded Arabic notes and source links. Download the original Word file ↗
Key points
- Prevention, stone types, hyperoxaluria, nephrocalcinosis, and practical 24-hour urine interpretation.