2.2 - Nephrolithiasis Flashcards
What is nephrolithiasis/urolithiasis?
Renal calculi (nephrolithiasis) and urinary calculi (urolithiasis) are masses of crystals, protein or other substances that my commonly cause urinary tract obstruction in adults
What are some risk factors for renal calculi formation?
- Age / Sex / Race
- Geographic location – rainfall, average temp., humidity, dietary patterns
- Seasonal factors
- Fluid intake- adequate water intake lowers risk
- Diet: High animal protein diet
- Occupation
- Genetic predisposition
- And co-morbidities, such as HTN, DM2, Obesity, Atherosclerosis, History of UTIs
- History of small bowel resection, gastric bypass and colectomy
- High urinary pH – MAIN risk factor for calcium oxalate and phosphate stones
- Age of development usually before 50 years of age
- Most kidney stones are unilateral
- Presence of kidney stones increases risk for CKD and MI
What medications are associated with renal stone formation:
- Colchicine
- Chemotherapy agents
- Vit D supplements
- Steroids
- Triamterene
- Indinavir- protease inhibitor
How are urinary calculi classified?
- Classified according to the primary minerals (salts) that make up the stones
- Calcium oxalate or phosphate – MOST common type (up to 85%)
- Struvite (magnesium, ammonium & phosphate) are approx. 1-5%
- Uric acid (5-10%)
- Location of the stone
What are staghorn/non-staghorn calculi?
- Staghorn calculi - large and fill the minor and major calyces (REFER TO IMAGE 1 BELOW)
- Non-staghorn calculi - variable sizes and are located in the calyces in the renal pelvis, or at various sites along the ureter (REFER TO IMAGE 2 & 3 BELOW)
How do renal calculi form?
Calculi formation is complex and is related to one of the following:
- Supersaturation of one or more salts in the urine
- Precipitation of the sales from liquid to a solid state (Crystallization)
- Stone or crystal growth through inhibiting substances
- Retention of crystal particles
What is urine supersaturation?
It is the presence of a higher concentration of a salt within a fluid (urine) than the volume is able to dissolve to maintain equilibrium; the salts form crystals that are retained and grow into stones.
What is urine crystallization?
- It is the process by which crystals grow from a small nucleus to larger stones in the presence of supersaturated urine.
- The pH of the urine also influences the risk of precipitation and calculus formation
- ****An alkaline urinary pH (>7.0) significantly increases the risk of calcium phosphate stone formation; whereas, acid urine (pH < 5.0) increases the risk of uric acid stone.
Describe how renal calculi are formed by stone/crystal growth inhibiting substances
- Substances such as potassium citrate, uromodulin pyrophosphate and magnesium are capable of crystal growth inhibition if they are not overwhelmed by the rate of supersaturation.
- Thus they can reduce the formation of calcium phosphate or oxalate stone formation
How does retention of crystal particles lead to renal calculi formation?
- This mainly occurs primarily at the papillary collection ducts.
- Most crystals are flushed through the system through ante grade urine flow, but certain situations can prevent prompt flushing of the crystals through the system, such as:
- Urinary stasis
- Anatomic abnormalities
- Inflamed epithelium within the urinary tract
- The size of the stone determines the likelihood of whether it will pass through the urinary tract and excreted through micturition:
- < 5mm stones have approx. 50% chance of passing
- 1cm or > stones have virtually NO chance of passing spontaneously
What are the subjective/physical exam findings associated renal calculi?
- There is moderate to severe pain often origination in flank and radiating to groin, usually indicating obstruction of the renal pelvis or proximal ureter
- Pain can be severe and incapacitating and be accompanied by nausea/vomiting
- If a stone is lodged in upper ureter, can produce pain referred to umbilicus.
- Gross blood (visible in urine) or microscopic hematuria (3 or more RBCs/hpf) may be present
- Testicular pain
- Costovertebral angle tenderness
- Pain not relieved by position
- Frequency, urgency, dysuria suggest stone is located in part of ureter within the bladder wall
- Acute renal failure may occur when both the collecting systems are obstructed by stones
What are some laboratory/diagnostic findings associated with renal calculi?
H&P combined with focused physical assessment and imaging studies are necessary for a complete workup
1. History should include:
- Dietary habits
- Age of first stone episode
- Stone analysis
- Presence of complicating factors
- Recent urinary tract infection
- Hyperparathyroidism history
- Recent GI or GU surgery
2. Obtain UA, including pH
3. 24 hour urine ordered to identify volume, pH, calcium, oxalate, citrate, uric acid, sodium, potassium and creatinine at minimum
4. Strain urine to obtain sample for stone analysis
5. Serum Chemistries: calcium, electrolytes, creatinine, phosphate and uric acid levels, CBC
6. Consider obtaining serum intact parathyroid hormone (PTH) as part of the screening evaluation if primary hyperparathyroidism in suspected.
What imaging studies can be done to diagnose renal calculi?
Imaging includes: (are necessary to quantify stone burden0
- Plain abdominal x-ray
- Ultrasound kidneys
- Intravenous pyelography (IVP)
- CT or MRI renal without contrast (renal stone protocol)
What are the goals of treatment for patients with renal calculi?
- Manage acute pain- PRIORITY of Treatment
- Promote stone passage – increasing urine flow rate with high fluid intake
- Reduce size of stones already formed or remove them: through percutaneous nephrolithotomy, ureteroscopy; laser lithotripsy to fragment stones for excretion into urine
- Prevent new stones from forming – adjust urine pH dependent upon stone lab analysis;
- An emergency situation can occur when obstructing kidney stones are present AND a proximal urinary tract infection. This may require emergent decompression, stone removal and IV antibiotics
How do you prevent the reoccurrence of urinary calculi?
- Increasing urine output to 2.5 L or more daily
- Avoiding colas and other soft drinks
- Avoid dietary oxalate: chocolate, beets, nuts, rhubarb, spinach strawberries, tea, wheat bran, okra
- Eat less animal protein
- Limit sodium intake
- Specific to calcium stones: maintain calcium intake of 1000-1200mg/day
