Kidney Stones for PA
Kidney Stones for Physician Assistant Licensing Exam
- Definition:
- Kidney stones (nephrolithiasis) are hard mineral deposits that form in the kidneys from substances in urine. They may vary in size and can obstruct the urinary tract, causing significant pain and complications.
- Types of Kidney Stones:
- Calcium Oxalate Stones:
- Most common (~80%). Form due to hypercalciuria, hyperoxaluria, and low urine volume. Risk factors include high dietary oxalate (e.g., spinach, nuts) and excessive sodium intake.
- Calcium Phosphate Stones:
- Develop in alkaline urine and are associated with renal tubular acidosis (RTA) and hyperparathyroidism.
- Uric Acid Stones:
- Form in acidic urine (pH <5.5) and are associated with hyperuricemia, gout, and high-purine diets (e.g., red meat, seafood).
- Struvite Stones:
- Composed of magnesium ammonium phosphate, these are associated with UTIs from urease-producing bacteria (e.g., Proteus, Klebsiella), often forming large staghorn calculi.
- Cystine Stones:
- Rare stones caused by cystinuria, a genetic disorder where excess cystine forms stones in acidic urine.
- Clinical Features:
- Renal Colic:
- Sudden, severe, sharp pain that starts in the flank and radiates to the groin. Patients are often restless and unable to find relief.
- Hematuria:
- Gross or microscopic blood in the urine due to irritation of the urinary tract.
- Nausea and Vomiting:
- Frequently accompany renal colic.
- Urinary Symptoms:
- Dysuria, urgency, and frequency may occur if the stone is near the bladder.
- Diagnosis:
- Urinalysis:
- Detects hematuria and may show crystals (e.g., calcium oxalate). If infection is present, pyuria and bacteriuria are noted.
- Non-contrast CT:
- The gold standard for diagnosis, detecting both radiopaque and radiolucent stones.
- Ultrasound:
- Preferred for pregnant patients or those needing to avoid radiation.
- Management:
- Conservative Treatment:
- For stones <5 mm, hydration and NSAIDs for pain control are recommended. Alpha-blockers (e.g., tamsulosin) may facilitate passage.
- Surgical Options:
- Extracorporeal Shock Wave Lithotripsy (ESWL) for stones <2 cm or ureteroscopy for stones in the mid or distal ureter.
- Prevention:
- Hydration: Aim for 2-2.5 liters of urine daily.
- Dietary Modifications: Low sodium, moderate calcium intake, limit oxalate-rich foods, and reduce animal protein.
- Medications: Thiazide diuretics for calcium stones, allopurinol for uric acid stones, and potassium citrate to alkalinize the urine.
Key Points
- Kidney stones are classified based on their composition, with calcium oxalate being the most common. Other types include uric acid, struvite, and cystine stones.
- Symptoms include sudden onset of severe flank pain, hematuria, and nausea. Fever may indicate infection and requires urgent evaluation.
- Non-contrast CT is the gold standard for diagnosis. Ultrasound is used in specific populations, such as pregnant patients.
- Conservative management includes hydration and pain control for smaller stones, while larger stones may require surgical intervention (e.g., ESWL, ureteroscopy).
- Prevention focuses on adequate hydration, dietary changes, and medications for patients prone to recurrent stones.