Can you still drink milk if you have calcium oxalate stones?

In this episode, Drs. Sophia Ambruso and Sarah Young welcome a new addition to the Kidney Essentials team, Dr. Parisa Mortaji! We also discuss why we care about nephrolithiasis (kidney stones) with a specific emphasis on calcium oxalate stones, why people form stones (hint: it's in the urine!!) as well as dietary counseling and additional medical interventions that improves stone absorption and prevents further stone formation!

Sophia Ambruso DO @Sophia_Kidney, Sarah Young MD @kidneycritic, Judy Blaine MD, Parisa Mortaji, MD

Transcript

Welcome to Kidney Essentials!

This is A Podcast for Medical students, residents and all nephro curious practitioners at the University of Colorado and beyond. We’re here to make nephrology more accessible one podcast at a time. Let’s start with introductions:

Sophie: I’m Sophie Ambruso, clinician educator at the denver VA and assistant professor on faculty at the University of Colorado. I tweet @Sophia_kidney and have no conflicts of interest.

Parisa: I’m Parisa Mortaji, hospitalist at the University of Colorado hospital.

Sarah:

Today we will be discussing kidney stones, and specifically calcium oxalate stones given these are the most common stones encountered in clinical practice. We will be focusing on history, workup, and prevention of stones.

Parisa, why don’t you start us off with a case:

Mr. Stoney is a 55 yo M with PMH of obesity and T2DM was referred to nephrology clinic by his PCP for nephrolithiasis. Patient was evaluated 3 weeks earlier after a recent ED visit for kidney stone. Thankfully, he was able to retrieve the stone which was sent off for composition analysis. Results are now back revealing calcium oxalate composition. The patient is worried whether or not he will have to give up his love for dairy products and this is his main concern he wants to address. 

So Sarah, can you tell us a little bit about the epidemiology of nephrolithiasis and why we care about it?

- Nephrolithiasis is very common and the prevalence is increasing in part 2/2 climate change and a rise in ambient temperatures

- also in the US there is geographic distribution of stones aka “stone belt” in southeast of US…joke about urologist should move south and east

- prevalence is double in men compared to women (19vs9)

Calcium oxalate is the most common type of kidney stone (~75%) that is typically bipyramidally shaped.

And why is it important for patients who have had a kidney stone to be evaluated?

·       More than half of individuals will develop recurrence within 10 years.

·       After an episode of nephrolithiasis, risk for recurrence is high: having passed a first kidney stone, patients have a risk of w15% to develop a second stone within a year and a risk of almost 50% within 10 years.

Which patients would benefit from a nephrology and/or urology consult for kidney stones?

·       Given such a high rate of recurrence as mentioned, it is recommended that all patients with kidney stones be evaluated at least once. Specialists can help determine stone composition and best next steps for stone treatment and prevention.

Okay so with that bit of background, Sophie what would you focus on in your history for this patient?

1) Detailed history is key and should focus on:

·       Number/ frequency of episodes of kidney stones

·       Medications, including vitamins and supplements

·       Thorough hx re: diet and fluid intake

·       Eval for malabsorptive conditions, h/o gastric bypass, family history of stones 

I think there is one specific dietary component our audience and our patient are curious about… CALCIUM!  How do we counsel him regarding his love for milk?  

·       The short answer is he can keep drinking milk!

·       HIGHER dietary calcium intake is associated with a LOWER risk of stone formation

o   This is due to reduction in intestinal absorption of dietary oxalate à which then leads to lower urine oxalate

·       Supplemental calcium, however, may increase the risk of stone formation

o   Why is this? ??Maybe due to timing of calcium supplements or higher total calcium consumption when taking supplements, leading to higher urinary calcium excretion

Let’s dive into other important dietary risk factors. The patient asks you how much he should drink to “flush the stones out.”

·       You want to make sure you are getting at least 2-2.5 L of fluid per day. Low fluid intake leads to decreased urinary volume which increases risk of stone formation. Good news is this fluid can include anything from water to coffee/tea/wine, but avoidance of sweetened beverages is prudent as sugar can increase urinary calcium excretion.

While taking the dietary history, the patient tells you he is drinking a spinach shake every morning to help him lose weight. Is this a problem?

o   A diet high in oxalate is one of the major risk factors for development of calcium oxalate stones. Oxalate: metabolic end-product; any dietary oxalate that is absorbed will be excreted in the urine. Spinach is one food group that is oxalate rich. Other examples include  soy products, rhubarb, nuts, sweet potatoes, and chocolate. 

Sophie, he also tells us he “has to have his red meat” at least once a day, and his salt shaker is a must have at the table. How do you respond to this?

·    Animal protein intake

o   Higher intake of animal protein may lead to increased excretion of calcium and uric acid and decreased urinary excretion of citrate

·    Sodium intake

o   High salt diet leads to decreased reabsorption of calcium and sodium in proximal tubule -> higher urinary calcium excretion

Any other dietary risk factors to be aware of?

·       Sucrose intake

o   Also leads to increased urinary calcium excretion

·       Potassium

o   Higher potassium intake decreases calcium excretion and increases urinary citrate excretion

·       Vitamin C

o   metabolized to oxalate which leads to higher levels of urinary oxalate

·       high fat diet

Sophie, what other elements in the history besides diet are important when assessing a patient with kidney stones?

·       Age, race (highest risk in middle-aged white men)

·       Obesity

·       T2DM (diabetic patients have lower urine pH which may increase the risk of uric acid calculi and higher urinary oxalate)

·       family history

o    risk is more than twofold greater with a family history of stone disease

o   primary hyperoxaluria (rare autosomal recessive disorder that causes endogenous oxalate production by the liver)

Okay so now that we have a fairly good grasp of important history elements and risk factors to be aware of, what laboratory workup-up is important?

rule out secondary causes of hypercalciuria -

·       basic labs including CBC, BMP, Ca, Ph, Mg, uric acid, UA, PTH, vitamin D 

·       Note: calcium oxalate stones are not influenced by urine pH, but keep this in mind for other stone compositions

·       24-hour urine collection (try to get 2 collections due to significant day to day variability; patient should continue normal diet for the collections): look at volume, calcium, oxalate, citrate, uric acid, sodium, potassium, phosphorous, pH, creatinine

·       Stone composition analysis

What are some disease processes that can lead to secondary calcium oxalate stones and should be ruled out with lab workup?

·       distal RTA

·       hyperparathyroidism (low calcium which is needed to bind oxalate)

·       sarcoidosis

·       malabsorptive disorders including IBD, CF, pancreatic insufficiency:

o   increased FFAs bind calcium in intestinal lumen -> calcium can no longer bind oxalate -> oxalate reabsorbed and forms stones

·       IBD (fat malabsorption – fat binds to calcium, oxalate absorbed and forms stones in kidney)

·       h/o gastric bypass (decreased calcium absorption à increased oxalate levels in urinary tract)

Let’s say secondary causes have been excluded. How do you counsel this patient to prevent recurrence of calcium oxalate stones?

Focus on modifying urine composition to reduce risk of new stone formation via diet and lifestyle changes including:

·       Increase fluid intake to achieve Urine volume at least 2L per day

·       low sodium <2.5g/d

·       Low animal protein

·       Normal dietary calcium intake (1200 mg/d), avoid excessive intake and try to avoid supplements

·       avoid vitamin C supplements

·       decrease intake of oxalate-rich foods 

·       Fat restricted diet

·       Recommendations are NOT temporary and need to be followed for a patient’s lifetime

What medications are commonly used to prevent recurrence of calcium oxalate stones?

·       Thiazide diuretics: inhibit NaCl co-transporter in the DCT. This then leads to increased proximal calcium reabsorption à decreased hypercalciuria. Maximum effect when patient adheres to low sodium diet. Can reduce recurrence by ~50%.

·       Potassium citrate: (citrate is a natural inhibitor of calcium stones); can be used if hypocitraturia detected on 24 hour urine collection

Take home points:

-        Calcium oxalate stones are the most common stone composition, making up roughly 75-80% of all kidney stones

-        A thorough dietary history should be taken to assess for consumption of high oxalate foods, inappropriately adhering to a low calcium diet, and a thorough med rec/ supplement rec (what out for vitamin c users!)

-        Urinary risk factors include a high urine calcium/oxalate, low urine citrate, and remember calcium oxalate stones are unaffected by urine pH

-        After secondary causes have been ruled out, treatment should focus on prevention of recurrence, namely through dietary and lifestyle changes, and at time with addition of certain medications

Well, I think that just about wraps it up! Thank you all so much for listening and I hope you enjoyed this podcast! Stay tuned for an upcoming podcast on ***. If there are any specific topics you want to hear about, feel free to message us on twitter!

Legal disclaimer: This podcast is for educational purposes only. The views and statements expressed on this podcast are soley those of the hosts. This podcast should not be used as medical advice or for treatment purposes