What is the appropriate workup for a patient with nephrolithiasis (kidney stones)?

From the Guidelines

A kidney stone workup should begin with a comprehensive history and physical examination, followed by urinalysis and basic blood tests, and imaging studies typically starting with a non-contrast CT scan or renal ultrasound, as recommended by the most recent guidelines 1. The initial evaluation of a patient with suspected kidney stones should include a thorough medical history, physical examination, and laboratory tests such as urinalysis to check for blood, crystals, and signs of infection. Basic blood tests including serum calcium, phosphorus, uric acid, creatinine, and electrolytes are essential to identify metabolic abnormalities.

• Imaging studies are crucial in the diagnosis of kidney stones, with non-contrast CT scan being the gold standard for initial imaging in patients with acute onset flank pain and suspicion of stone disease, according to the American College of Radiology 1.
• For patients with their first kidney stone, these initial tests are usually sufficient. However, recurrent stone formers should undergo a more extensive metabolic evaluation including 24-hour urine collection to measure volume, pH, calcium, oxalate, citrate, uric acid, sodium, and creatinine, as recommended by the American College of Physicians 1.
• Stone analysis, when available, provides valuable information about composition to guide prevention strategies. Based on these results, specific interventions can be recommended, such as increased fluid intake (2-3 liters daily), dietary modifications (reduced sodium, animal protein, and oxalate), or medications like thiazide diuretics for hypercalciuria, allopurinol for hyperuricosuria, or potassium citrate for hypocitraturia.
• The American Urological Association also recommends obtaining a non-contrast CT scan on patients prior to performing percutaneous nephrolithotomy (PCNL) and a urinalysis prior to intervention, with urine culture if urinary tract infection is suspected 1.
• Overall, a comprehensive approach to kidney stone workup and management helps identify underlying causes and develop targeted prevention strategies to reduce recurrence risk.

From the Research

Kidney Stone Workup

• The initial evaluation of kidney stones involves excluding concomitant infection, imaging with a non-contrast computed tomography scan, and consideration of medical expulsive therapy or surgical intervention depending on stone size and location 2.
• The use of non-contrast computed tomography (CT) scans is recommended for the diagnosis of kidney stones due to its high sensitivity and specificity 3.
• Stone size and location are significant factors in determining treatment outcomes, with larger stones and those in certain locations being more likely to require further treatment 4.
• Metabolic evaluation is also an important part of the workup, with increasing fluid intake recommended to reduce the risk of recurrence 2.
• The mean attenuation value (MAV) of the stone, as measured by CT scan, may be a useful predictor of treatment success, with higher values indicating a lower likelihood of successful treatment 4.

Imaging and Diagnosis

• Non-contrast helical CT is a valuable tool in the diagnosis of kidney stones, allowing for rapid and accurate diagnosis without the need for contrast media 3.
• The use of non-contrast-enhanced CT scans may not provide significant advantages over kidney-ureter-bladder (KUB) films in all cases, but can be useful in certain scenarios 4.
• Imaging studies should be used to guide treatment decisions, taking into account factors such as stone size, location, and density 4.

Treatment and Management

• Medical expulsive therapy or surgical intervention may be considered depending on stone size and location 2.
• Extracorporeal shock wave lithotripsy (ESWL) is a safe and efficient treatment option for urinary stone disease, with an overall stone-free rate of 85% in one study 4.
• The outcome of ESWL can be influenced by factors such as stone size, location, and density, as well as the skin-to-stone distance (SSD) and mean attenuation value (MAV) of the stone 4.

Note: The study 5 is not relevant to the topic of kidney stone workup.