Nephrolithiasis for Health Professionals

• Nephrolithiasis refers to kidney stones
• This presentation is for allied health professionals
• Dr. Barry Cohen is the presenter, date is March 10, 2025

Objectives

• Discuss the epidemiology of nephrolithiasis
• Discuss the pathophysiology of nephrolithiasis
• Overview the types of kidney stones
• Discuss causes and risk factors
• Identify patients needing referral
• Understand the evaluation process for patients with kidney stones
• Review general and specific management strategies

Case Study

• A 50-year-old male presents with recurrent nephrolithiasis
• The patient's history includes an episode of renal colic four years prior
• ESWL was required to remove a 1.1 cm stone
• The patient reports spontaneously passing four small stones, all calcium oxalate
• The patient's physical examination is normal
• Bloodwork results were normal
• Urinalysis showed a urine pH of 5.5 with no crystals
• A 24-hour urine collection revealed low urine volume, high sodium excretion, and high calcium excretion
• Renal ultrasound shows a single 2 mm stone in each kidney

Epidemiology

• Kidney stones occur in 15-20% of all men and 7-10% of all women
• The overall incidence of kidney stones has been increasing
• Kidney stones recur in 35-50% of patients within 5 years
• Kidney stones are most common in white men and least common in black women
• Peak age happens between 40 and 60 years old
• Kidney stones may be more common than chronic kidney disease (CKD)

Pathophysiology

• Stone formation requires a high concentration of substances like calcium in urine, leading to crystallization
• Epitaxy is the ability of one crystal to grow on another, facilitating aggregation
• Deficiency in urinary inhibitors like citrate can promote stone formation
• Urinary pH plays a role in stone formation

Stone Types

• Calcium Oxalate is the most common type, accounting for 60-70% of stones
• Calcium Phosphate stones account for 10-20%
• Uric Acid stones represent 10-15% of cases
• Struvite stones make up about 4%
• Other types, like cystine stones, occur in about 1% of cases

Causes and Risk Factors of Calcium Stones

• Hypercalciuria or hypercalcemia, metabolic acidosis (especially RTA), medullary sponge kidney are possible causes
• Other causes include hyperparathyroidism and idiopathic factors
• Hyperoxaluria caused by excessive vit C ingestion or fat malabsorption syndromes
• Hypocitraturia or idiopathic factors related to acidosis or hypokalemia
• Hyperuricosuria is related to hyperuricemia or diet
• Low urine volume contributes
• Alkaline urine CaPhos promotes calcium phosphate stone formation

Causes and Risk Factors of Other Stone Types

• Uric acid stones are caused by low urine volume, hyperuricosuria, both with or without gout, and acidic urine
• Struvite stones are caused by low urine volume, UTI (upper tract), and alkaline urine
• Cystine stones are caused by low urine volume, cystinuria and are hereditary

Referral

• Patients with recurrent stone formation need to be referred
• Children with stones need to be referred
• Patients with a single stone but multiple risk factors such as family history and fat malabsorption, need a referral

Evaluation

• History should include an assessment of the onset, frequency, and severity of symptoms
• Severity includes interventions, ER visits, pain control
• Look for medical risk factors such as GI disease, RTA (Renal Tubular Acidosis), family history, and anatomical variations such as Medullary Sponge Kidney
• Review of medication, such as Vit C, Acyclovir & Topiramate
• Review fluid intake, sodium intake, animal protein intake, oxalate intake such as nuts, green veggies, rhubarb, chocolate, black tea etc & calcium intake
• Physical examination includes a general exam including blood pressure
• Lab includes routine electrolytes (K, bicarb), Ca, alb, Phos, iCal, PTH, Uric acid, U/A (pH, crystals)
• 24 hr urine for volume, Na, urea, Ca, Ox, urate, citrate, phosphate, and cystine
• Stone analysis to assess stone composure
• Imaging includes KUB, U/S, CT

Management - General

• Acute care is managed by urology
• Chronic care and prevention are managed by nephrology
• Treatment is more aggressive relative to perceived disease burden

Management - Specific

• Treat the underlying cause for calcium stones
• Increase fluid to 2.5L, low salt, animal protein, and oxalate, normal calcium and high citrate
• If serious disease, use Indapamide for hypercalciuria
• Alternately, use, amiloride as adjunct or for hypokalemia, Kcit for acidosis or hypocitraturia, Allopurinol for hyperuricosuria & Calcium citrate for enteric hyperoxaluria
• Remove any offending meds such as vit C
• Treat underlying cause for urate stones
• Increase fluid to 2.5L, low animal protein
• If serious disease, use, Allopurinol for hyperuricosuria & Kcit to alkalinize the urine
• Struvite, treat UTI
• Cystine, increase fluid intake to 4-5 L/d, alkalinize the urine with Kcit, use penicillamine and tiopronin

Returning to the Case

• A 50 yo male presents to your clinic with recurrent nephrolithiasis
• This began four years with an episode of renal colic; ultimately ESWL was requires to remove a 1.1 cm stone
• Since then, he has spontaneously passed four small stones, all composed of calcium oxalate
• The patient's physical examination is normal
• Bloodwork results were normal
• Urinalysis showed a urine pH of 5.5 with no crystals
• A 24-hour urine collection revealed low urine volume, high sodium excretion, and high calcium excretion
• Renal ultrasound shows a single 2 mm stone in each kidney

Plan

• Perform a thorough dietary review
• Advise a diet high in fluid (2-3 L/d), low in Na and animal protein, normal in calcium, and low in oxalate
• Consider indapamide to treat hypercalciuria

Take Home Points

• Kidney stones affect 20% of all men and 10% of all women, with up to a 50% recurrence rate
• Work up includes chemistry, U/A, 24 hr urine, and imaging
• Recurrent stone formers, children, and patients with an identified secondary cause require a workup/referral
• Advise a diet high in fluid, low in sodium, and low in animal protein
• Medications: indapamide (for hypercalciuria), Kcit (for hypocitraturia to alkalinize urine) & allopurinol (hyperuricosuria)