Nephrolithiasis - Kidney Stone Disease

Indications for Testing

Testing should be considered when an individual presents with signs and symptoms of nephrolithiasis, is diagnosed with a kidney stone, or has a recurrence of stones. Patients tend to present with pain in the back, abdomen, or groin, nausea and/or vomiting, fever and chills, or other symptoms of a urinary tract infection, including blood in the urine, cloudy urine, a frequent urge or inability to urinate, or pain with urination.  In younger children, the signs may be more subtle and include irritability and changes in urinary habits. 

Criteria for Diagnosis

Diagnosis of nephrolithiasis is confirmed when a stone has passed, has been extracted or destroyed, or has been identified by imaging studies. Urinalysis that demonstrates hematuria can also help to confirm the diagnosis if the rest of the clinical picture is consistent with nephrolithiasis. 

Laboratory Testing

Metabolic evaluation and stone composition analysis are recommended for patients with recurrent stones or patients with an initial stone who are at high risk of recurrence, including those with a family history, pediatric patients, and young adult patients.  Other tests may be performed as part of an initial workup in patients with a first stone to narrow the differential diagnosis, evaluate for concomitant infection, or assess renal function.    

Initial Workup

When a patient presents with signs and symptoms of nephrolithiasis, a urinalysis that includes detection of blood should be performed. The presence of hematuria can support the diagnosis of a kidney stone in the appropriate setting. In patients with a new diagnosis of nephrolithiasis, a routine metabolic panel and urinalysis in addition to a detailed medical and dietary history are a good starting point for a basic evaluation. Chemistry tests should include serum/plasma electrolytes, calcium or ionized calcium, creatinine, and uric acid. The results could indicate an underlying medical condition that may be associated with kidney stone disease. Urinalysis should include a dipstick with pH and microscopic evaluation for crystals. If the urinalysis is suggestive of a urinary tract infection, a urine culture should be performed.  

Further Metabolic Evaluation

Additional metabolic testing should be performed in patients at high risk of stone recurrence or who have a personal history of stones. Testing for concentrations of urinary salts can be used to determine risk factors and guide treatment protocols. This evaluation should consist of one or two 24-hour urine collections (two are better) tested for volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine. If a cystine stone is found, urine amino acid analysis should be performed.  

Stone Composition

When a stone is available, particularly in the case of a patient with stone recurrence or an individual at high risk of recurrence, stone analysis should be performed. For those with recurrent stones, analysis may be performed on subsequent stones, especially if the patient is not responding to treatment or there is suspicion of a different type of stone, given that stone composition can change over time.   Stones are analyzed for heterogeneity, and the different components are tested separately. The clinically significant crystalline components identified in the specimens are reported and may guide medical or preventive management of the patient. 

Pediatrics

Comprehensive testing should be pursued in the first episode of a kidney stone in a pediatric patient due to the high risk of a metabolic disorder causing the stone formation. Stone composition analysis is recommended, if possible. Urinalysis and microscopic evaluation for crystals, urine culture, and a basic metabolic panel including calcium, magnesium, phosphorus, uric acid, and creatinine should be performed in any child with kidney stones. Evaluation of a 24-hour urine specimen for urine volume, pH, sodium, calcium, creatinine, citrate, oxalate, magnesium, phosphate, and creatinine should be performed when possible to evaluate for underlying metabolic abnormalities and other risk factors. Testing for cystinuria involves amino acid analysis for cystine, arginine, lysine, and ornithine on a urine sample and should be performed in patients with cystine stones or cystine crystals seen on microscopic evaluation of the urine.