Nephrolithiasis: Clinical sciences

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Introduction0:00–0:36

Nephrolithiasis, also known as renal calculi or renal stones, is a painful condition where crystals form in the kidney, potentially causing urinary tract obstruction.
Renal stones usually form when urine becomes oversaturated with minerals and salts, including calcium, oxalate, and uric acid.
Common renal stone types include calcium oxalate-, calcium phosphate-, uric acid-, cystine-, and struvite stones. Now, if your patient presents with a chief concern suggesting nephrolithiasis, you should first perform an ABCDE assessment to determine if your patient is unstable or stable.

Unstable Patient0:36–1:40

If unstable, stabilize the airway, breathing, and circulation. Next, obtain IV access and put your patient on continuous vital sign monitoring, including blood pressure, heart rate, and pulse oximetry.
Finally, if needed, provide supplemental oxygen.Now, here’s a clinical pearl to keep in mind! Nephrolithiasis associated with a urinary tract infection is a medical emergency that requires immediate decompression and drainage.
Left untreated, it can cause complications such as pyelonephritis, renal abscess, or even sepsis. Nephrolithiasis is also an emergency when it occurs alongside renal failure, anuria, bilateral ureteral obstruction, or a single-functioning kidney.
In these cases, consult the urology team immediately.Now that we're done with unstable patients, let’s go back to the ABCDE assessment and discuss the stable ones.

Stable Patient1:40–2:17

In these individuals, first, obtain a focused history and physical examination and order a urinalysis. Patients with nephrolithiasis typically present with an acute onset of excruciating flank pain, along with hematuria.
They may also experience dysuria, nausea, or vomiting. The physical examination usually reveals unilateral flank tenderness, and urinalysis can show red blood cells, white blood cells, and crystals in the urine.
If your patient presents with these findings, you should suspect nephrolithiasis. Next, order a non-contrast helical CT scan of the abdomen and pelvis to check for stone presence.

Suspect nephrolithiasis2:17–3:17

If there’s no stones on the scan, then consider alternative diagnoses. Alternatively, if the CT scan reveals a stone, that confirms the diagnosis of nephrolithiasis.
Now here’s a clinical pearl to keep in mind! When suspecting nephrolithiasis, a helical CT scan is the preferred imaging choice over both X-rays and ultrasound, because it can detect both radiolucent and radiopaque stones as small as 1 mm.
Additionally, this imaging method can identify hydronephrosis. X-rays can only detect larger radiopaque stones; while ultrasound can detect hydronephrosis, but it is not reliable for identifying stones beyond the proximal ureter.Now, once you diagnose nephrolithiasis, your next step is pain management.

Pain management3:17–3:43

This can be achieved with an intravenous nonsteroidal anti-inflammatory drug, or NSAID, such as ketorolac. Avoid opioids whenever possible, as NSAIDs provide effective pain relief and have fewer adverse effects.
Opioids are reserved for patients with contraindications to NSAIDs, severe kidney function impairment, or those with inadequate pain relief with NSAIDs.After pain management, review the CT scan to assess the stone size, which will guide treatment.

Stone ≥ 6mm 3:43–4:05

If the stone measures 6 millimeters or more, it's unlikely to pass on its own, so you should consult the urology team to discuss treatment options.
These can include extracorporeal shock wave lithotripsy, or endoscopic removal. On the other hand, if the stone is less than 6 millimeters, it’s possible that it might pass on its own.

Stone < 6mm 4:05–5:15

In this case, observe your patient for spontaneous stone passage for 4 weeks and instruct them to strain their urine using a calculi strainer, and save any stones they pass.
Additionally, consider prescribing alpha-blockers, such as tamsulosin, as this can help relax the ureteral smooth muscle to facilitate stone passage.
Next, assess whether or not the stone has passed after 4 weeks. If there is no evidence of stone passage within this time frame or if the patient continues to experience symptoms, obtain a urological consult for extracorporeal shock wave lithotripsy or endoscopic removal.
Also, keep in mind that patients with unpassed renal stones are at a high risk for developing hydronephrosis. So make sure you follow these patients with a renal ultrasound every 2 weeks, to ensure there’s no hydronephrosis or proximal ureteral obstruction.
On the flip side, if the stone passes, no further consultations are needed. Now, no matter whether the stone is removed by the urology team or passed on its own, you should always assess the stone type in order to find the best way to prevent recurrence!

Assess the stone type5:15–5:41

This involves ordering labs, including a 24-hour urine collection for urinary pH and levels of calcium, oxalate, citrate, uric acid, and phosphorus.
Additionally, order a urine microscopy, and renal stone composition analysis. If the 24-hour urine test shows high levels of urine calcium and oxalate, low levels of urine citrate; the stone composition analysis reveals calcium oxalate; and urine microscopy reveals envelope or dumbbell-shaped crystals, you can diagnose calcium oxalate stones.

Calcium Oxalate Stone5:41–6:20

Treatment involves thiazide diuretics to lower urine calcium excretion, potassium citrate to alkalinize the urine, as well as a diet that is low in sodium, oxalate, and non-dairy animal protein.Alternatively, if 24-hour urine reveals high urine calcium and phosphate; low urine citrate; a pH greater than or equal to 6.5; and urine microscopy shows amorphous wedge-shaped crystals in a rosette pattern, diagnose calcium phosphate stones.

Calcium Phosphate Stone6:20–7:18

In this case, the treatment is primarily based on thiazide diuretics to reduce urine calcium excretion and a low-sodium diet.
Now, here’s a clinical pearl! Serum calcium levels are often included in the workup of renal stones to screen for hyperparathyroidism.
If they’re elevated, check parathyroid hormone levels to evaluate for primary hyperparathyroidism, as well as 25-hydroxy vitamin D levels to evaluate for secondary hyperparathyroidism due to vitamin D deficiency.
Both these conditions are commonly associated with the development of calcium phosphate stones.Next, if labs indicate a urine pH of 5.5 or lower and urine microscopy reveals rhomboid-shaped crystals, diagnose uric acid stones.

Uric Acid Stone7:18–7:59

First-line treatment involves urine alkalinization with potassium citrate, and a low non-dairy animal protein diet. If the first-line treatment fails, you may give a xanthine oxidase inhibitor like allopurinol to decrease serum uric acid production.
Additionally, it’s important to optimize management of underlying conditions like diabetes, obesity and gout, since uric acid stones are commonly observed in these patients.Now, if urine microscopy shows hexagon-shaped crystals, and stone composition analysis confirms cystine, diagnose cystine stones.

Cystine Stone7:59–8:28

First-line treatment for preventing their recurrence involves urine alkalinization using potassium citrate, along with a low sodium and low non-dairy animal protein diet.
If first-line treatment fails, chelating agents like penicillamine, which bind to cystine, can be considered.Finally, if labs demonstrate a urine pH over 8, and urine microscopy reveals coffin lid-shaped crystals, diagnose struvite stones, also called magnesium ammonium phosphate, or triple-phosphate stones.

Struvite Stone8:28–9:44

Struvite stones are commonly associated with urinary tract infections caused by urease-producing bacteria, so treat any concurrent infection and take measures to prevent future urinary tract infections to minimize stone recurrence.
Now, here’s a high-yield fact to keep in mind! Struvite stones form within the lumen of the renal pelvis and extend into one or more of the renal calyces.
These stones are often quite large and take on a classic staghorn appearance on imaging, and can create the potential for obstruction.
Therefore, urological consultation for stone removal is often necessary. And finally, one last clinical pearl!
Regardless of stone type, adequate fluid intake is effective for preventing future stone formation. So all patients should be encouraged to drink enough fluid to dilute urine and maintain a urine output of at least 2.5 liters every 24 hours.
Alright, as a quick recap… Once you suspect nephrolithiasis, order a non-contrast helical CT scan. If the CT scan reveals a stone, diagnose nephrolithiasis and initiate pain management, primarily with IV NSAIDs.

Review9:44–10:45

Next, assess the stone size. For stones measuring 6 millimeters or more, consult the surgical team for extracorporeal shock wave lithotripsy or endoscopic removal.
If the stone is less than 6 millimeters, observe your patient for spontaneous stone passage for 4 weeks. Sometimes the stone passes on its own; but if not, or if the patient continues to experience symptoms, again, consult the urology team.
Now, in all individuals, no matter whether their stone is removed by the surgery team or passed on its own, you should order urine studies to differentiate between different stone types, including calcium oxalate, calcium phosphate, uric acid, cystine, and struvite stones.
Nephrolithiasis: Video, Causes, and Symptoms | Osmosis