If you're at risk for kidney stones or you've already experienced one of these painful little buggers, your urologist has likely drawn blood for a metabolic workup at some point. (A metabolic workup is more formally known as a comprehensive metabolic panel or CMP.)
But what is a metabolic workup for kidney stones? We asked Victoria Webber, a physician assistant in our Plymouth Care Center, to share her insights.
As with all content on our blog, the following is educational, not medical advice. Always consult your medical provider regarding your unique healthcare needs.
Could you explain what a metabolic workup for kidney stones is and what it typically includes?
VICTORIA WEBBER: A metabolic workup is a series of blood tests and a urine test for patients with a history of kidney stones that we deem to be "high risk" for developing recurrent stones or complications from stones.
Metabolic workups help us determine if there is an underlying disorder causing stone formation and guide us in preventing future stone formation through changes in diet or medications.
The metabolic workup for kidney stones includes the following:
Blood tests:
- Basic metabolic panel (BMP) – This checks electrolytes and kidney function
- Calcium
- Uric acid
- Parathyroid hormone
- Vitamin D
24-Hour Urine Test: The patient collects urine for 24 hours and brings it to a lab to be analyzed for total urine volume, citrate, oxalate, calcium, sodium, uric acid, phosphate, and other levels.
What key indicators or biomarkers do you look for in a metabolic workup for kidney stones, and what can they tell you about a patient's health?
VICTORIA WEBBER: The first value I always check is a patient's urine output since dehydration is the most common cause of stone formation. (Test your kidney stone knowledge here.)
In your experience, how crucial is a metabolic workup in kidney stone management?
VICTORIA WEBBER: The information we learn from the metabolic workup is vital for managing high-risk stone patients. This high-risk demographic includes the following:
- Patients with a history of a large stone burden or multiple kidney stones
- Patients at high risk of complications from stones (patients with a solitary kidney)
- Pediatric patients with kidney stones (note: I don't see these patients since I don't work in pediatric urology)
- Patients with a history of stones and medical, genetic, or anatomic conditions that increase the risk of future stones (e.g., gout, Crohn's disease, hyperparathyroidism, and medullary sponge kidney)
Do patients need to do any special preparations before undergoing a metabolic workup? How do these preparations impact the accuracy of the results?
VICTORIA WEBBER: You shouldn't change your diet or fluid intake before completing the metabolic workup since this could affect your results and "cover up" the reasons you're forming stones.
Remember, a metabolic workup aims to get an accurate baseline to determine what has likely been causing the stone formation. For example, if you change your diet on the day of the 24-hour urine collection, the results will not be helpful.
You should plan to do the urine test on a day when you can spend most of your time at home since you won't want to carry a jug of urine around with you all day.
You should also wait at least one month after the last stone event (i.e., surgery for kidney stones or passing a stone) before completing a metabolic workup since this will cause inaccurate results due to the recent stress on your kidneys.
Patients often have access to the results of their metabolic workups in their online portal. What advice do you have for them as they review their results, especially if any numbers fall outside the normal range?
VICTORIA WEBBER: I know it can be tempting, but don't try to interpret these results on your own. Review them with your healthcare provider because the results can be difficult to interpret and aren't always straightforward. We interpret the 24-hour urine and blood work results together (one informs the other).
How often do you run metabolic workups as part of your management for kidney stones?
VICTORIA WEBBER: The initial metabolic workup provides a baseline. If any changes are made (medications or lifestyle modifications, for example), we can repeat the workup after six months and as needed.
Is there anything else you'd like to convey about metabolic workups for kidney stones?
VICTORIA WEBBER: If you're a recurrent stone former and looking for ways to prevent future stones, discuss obtaining a metabolic workup with your provider. We're accepting new patients at GBU, so if you're in Massachusetts, feel free to reach out.
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