From the Guidelines
Point-of-care urinalysis is a valuable screening tool for kidney stones, particularly when it shows hematuria, which is present in approximately 85% of kidney stone cases. The presence of hematuria, as discussed in the study by the American College of Physicians 1, is a significant indicator that warrants further investigation, including a thorough medical history and possibly imaging studies like CT scans. Other urinalysis findings that may suggest kidney stones include:
- Crystalluria, especially calcium oxalate, calcium phosphate, or uric acid crystals
- An alkaline or acidic pH, which may indicate specific stone compositions
- Pyuria, indicating inflammation
- Proteinuria, which can sometimes occur in the presence of kidney stones
It is essential to consider these urinalysis findings in conjunction with clinical symptoms such as flank pain, nausea, vomiting, and painful urination. While point-of-care urinalysis provides valuable information, it has limitations, including the inability to determine stone size, location, or whether urinary tract obstruction exists, which are crucial factors in treatment decisions. Therefore, if point-of-care urinalysis suggests kidney stones, further evaluation with imaging studies is recommended for a definitive diagnosis. This approach is supported by the American College of Physicians' recommendations for the evaluation of patients with hematuria 1.
From the Research
Poct Urinalysis Evidence of Kidney Stone
- Urinalysis is a crucial diagnostic tool for kidney stones, as it can help identify the presence of blood, protein, or other abnormalities in the urine 2.
- A study published in 1998 found that calcium oxalate crystals were detected in 27% of stone formers and 18% of control subjects in vesical urine, and in 36% of stone formers and 27% of control subjects in renal urine 3.
- The presence of uricosuria, calciuria, magnesiuria, and calcium oxalate molar product in urine can increase the risk of kidney stone formation 3, 4.
- Urinalysis can also help identify other risk factors for kidney stone formation, such as hyperuricosuria, hypercalciuria, hyperoxaluria, and hypocitraturia 4, 5.
- A nonsteroidal anti-inflammatory drug is the first drug of choice for pain management in patients with kidney stones, and medical expulsive therapy (MET) is considered first-line therapy if stones do not resolve with observation 2, 5.
Urine Test Results
- Hematuria (blood in the urine) is a common symptom of kidney stones, and urinalysis can help detect its presence 2, 5.
- Proteinuria (protein in the urine) can also be detected through urinalysis, and may indicate kidney damage or disease 2.
- The presence of leukocyte esterase or nitrites in the urine can indicate a urinary tract infection, which can increase the risk of kidney stone formation 5.
Diagnostic Criteria
- Renal ultrasonography is the recommended first-line imaging modality for diagnosing kidney stones, and is preferred in pregnant patients 2.
- Metabolic testing is recommended in high-risk patients, such as those with a family history of stones, one kidney, malabsorption or intestinal disease 2.
- Urinalysis and imaging studies can help confirm the diagnosis of kidney stones and assess for conditions requiring active stone removal 5.