Risk factors for stone formation are categorized into intrinsic and extrinsic causes. Intrinsic causes include age, family history and sex. The peak age of presentation is 40-60 years old. Patients with a first degree relative with renal stones have an increased risk (RR 2.5). 3The relative risk between men and women has narrowed over the past decade from 3:1 to 1.3:1 (ibid). Obesity, fluid intake and diet are the most important extrinsic risk factors. There is a strong correlation between BMI and stone formation. A BMI of >27.5 doubles the relative risk compared with a BMI of 20-22.5. 4 Fluid intake is inversely correlated with stone formation. Consuming >2500 mls/day halves the relative risk compared with <1250 mls/day. 5 A low meat intake (<50g/day) halves the risk of stone formation compared with a high meat intake (>100g/day). 4 Perversely a low, rather than high, calcium diet predisposes to calcium stone formation. 5 PresentationThe majority of renal stones remain asymptomatic. Up to 5% of abdominal ultrasounds and CTs find incidental renal stones.6 Small non-obstructing stones within the kidney are typically asymptomatic or have mild symptoms. The most common presentation of a renal stone is loin pain caused by ureteric obstruction. The classical presentation is severe colicky pain which reaches its peak within 1-2 hours and then becomes constant. Hospital presentation within 12 hours of onset of the pain is a significant predictor of renal colic.7 The location of the stone within the ureter determines the nature of the pain. The most common sites are the pelvico-ureteric junction (PUJ), the pelvic brim and vesico-ureteric junction. PUJ stones typically present with a deep loin pain without radiation, pelvic brim stones with flank or lower quadrant pain radiating into the groin and vesico-ureteric stones with irritative voiding symptoms. Flank pain is not specific to renal stones with stones being demonstrated on CT in 34-73% of these patient. Nausea, vomiting and a change in appetite are present in approximately 50% of cases.7 Other less common symptoms of renal stones include visible haematuria, recurrent urinary tract infections and the painless passage of grit. On examination, loin tenderness may be present in up to 86% of patients.7 Flank and iliac fossa tenderness may be palpated, but there should be no signs of peritonitis. A thorough examination of patient should be performed to rule out the red flags and other differentials mentioned below. InvestigationsDetection of haematuria on urine dipstick is the most discriminating bedside investigation. It has a sensitivity for renal stones of 84%, specificity of 48%, PPV of 72% and NPV of 65%.8 It should be noted that the sensitivity is 95% on day 0 from the onset of pain but decreases to 65% by day 3.9 Low dose non-contrast-enhanced CT (CT KUB) is the gold-standard investigation for most adults, with a sensitivity and specificity of 95% and 98%.9,10 All renal stone types are detectable by CT KUB except for Indinavir stones. These rare stones form as a...
Risk factors for stone formation are categorized into intrinsic and extrinsic causes. Intrinsic causes include age, family history and sex. The peak age of presentation is 40-60 years old. Patients with a first degree relative with renal stones have an increased risk (RR 2.5). 3 The relative risk between men and women has narrowed over the past decade from 3:1 to 1.3:1 (ibid). Obesity, fluid intake and diet are the most important extrinsic risk factors. There is a strong correlation between BMI and stone formation. A BMI of >27.5 doubles the relative risk compared with a BMI of 20-22.5. 4 Fluid intake is inversely correlated with stone formation. Consuming >2500 mls/day halves the relative risk compared with <1250 mls/day. 5 A low meat intake (<50g/day) halves the risk of stone formation compared with a high meat intake (>100g/day). 4 Perversely a low, rather than high, calcium diet predisposes to calcium stone formation. 5 Differential diagnosisOther renal causes of acute flank pain include: pyelonephritis (typically fevers, rigors and vomiting with infection evident on urine dipstick); blood clot ureteric obstruction (secondary to frank Citation: Menzies-Wilson R, Folkard S, Somani B. Management of renal Stones for the non-specialist. Int J Fam Commun Med. 2018;2(2):38-41.
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