Kidney Stones, Kidney Function, Kidney Disease

Glomerular filtration is the main life sustaining kidney function, and kidney stones can cause enough damage to lower it. Usually the reduction is very modest, but sometimes stones can cause kidney failure. This means, like all diseases, stones are best prevented as early and as completely as possible.

This ‘just the facts’ version tells about what filtration is, how physicians measure it, how much kidney stones lower it, and how often that occurs.

Two longer articles give the details. One is comprehensive. The other focuses on only kidney disease, but is long.

Much of this text is redacted from the other two articles. I left out pictures, data, and links to PubMed to emphasize the main points.

The featured painting is by You Si 游思 (b. 1954), based in Shanghai, China. He is the son of two artists who lived through the cultural revolution and paints in new ways. I think his work is gorgeous but could not find a serious biography or critical study, or any museums that show his work.

What Filtration Is

Our two kidneys are each made up of about one million nephron units. A nephron is a complete and complex structure that begins its function by filtering from blood plasma a clear solution of water and small molecules. That filtrate enters the long loopy tubule of the nephron that reabsorbs a vast fraction of water and salts back into the blood leaving behind only that destined for export out of the body.

The glomerulus, a tuft of capillaries nestled in a tiny cup that drains into its tubule, performs this filtration. So we name it glomerular filtration rate, or GFR.

Blood flow and pressure from the heart drive filtration, but kidneys can regulate its rate. The cells that line the tubules regulate what fractions of innumerable individual salts and small molecules are taken back or let go into the urine.

Filtration Keeps Us Alive

Filtration rids the blood plasma of metabolic wastes, like oxalate, and permits us to excrete the extra water, salt, and all other materials we might eat or drink every day. Without filtration we need dialysis or transplantation to continue living. So this kidney function stands above all the others. When physicians speak of kidney function, they mean, and measure, filtration.

Filtration and Kidney Stones

Kidneys filter copious volumes of water and small molecules – like calcium, oxalate, citrate, phosphate, uric acid, sodium – hundreds of distinct materials. They then return most of this flood – 100 to 200 liters a day of water alone – back into the blood keeping behind only what they destine for export as urine.

Because kidneys filter such vast amounts, very subtle variations in what they take back into blood can load the urine with stone forming salts like calcium and oxalate, and cause stones. In other words, stones arise in significant measure because of subtle imbalances between filtration and reabsorption of key materials like calcium, oxalate, citrate, and water itself.

The filtering system, though powerful, is delicate. Through obstruction, infection, loss of one kidney, or surgical trauma stones can injure it. Such injuries reduce the ability of kidneys to protect the body, and when severe can lead to chronic kidney disease and even need for dialysis or transplantation.

How We Measure Glomerular Filtration

Serum Creatinine

Muscles make creatinine steadily and send it into the blood. Like almost all small molecules, kidneys filter it. Serum creatinine therefore reflects the balance between muscle production and filtration. When filtration falls serum creatinine rises. It is like your golf score – bad day, higher score. Serum creatinine gauges filtration adequately enough for clinical practice. But because kidneys not only filter creatinine but also secrete it from blood into urine, creatinine overestimates true filtration.

eGFR

To get a better estimate, scientists compared serum creatinine to true GFR in reasonably large populations and calculated the best fit between them using regression techniques. The resulting regression equation gives estimated GFR, or eGFR, from serum creatinine, age, sex, and race. This highly derived index dominates medical practice. When physicians speak of reduced kidney function they mean reduced eGFR.

Kidney Function in  Stone Formers

Average Function is modestly reduced

Our Own Patients

In our own patients, we found that stone formers have lower kidney function than normal people. The common idiopathic calcium stone formers are just slightly low. Likewise for those with primary hyperparathyroidism. But kidney function is reduced by about 20% in people who make stones because of bowel disease or diseases like renal tubular acidosis or cystinuria. Uric acid and struvite stone formers have even greater reductions.

US Health Surveys

The national NHANES data survey results showed modestly reduced kidney function in overweight people who had a history of stones. Women who formed stones had increased risk for serious chronic kidney disease, and even dialysis.

Olmsted County 

This community uses Mayo Clinic for care so records are very complete. A history of kidney stones increased risk of CKD and eventual dialysis.

Large Reviews

Two extensive reviews of all published studies – not just the few I mentioned – concluded that where ever looked for, stone forming raised risk of high blood pressure, serious chronic kidney disease, and even dialysis.

Though Increased, Kidney Disease Rates are Not High

Stones raise the risk of serious kidney disease from the very low levels in the general population to higher though still low levels. The vast majority of stone formers do well and never have problems that require special kidney care. Only rarely do stone formers need dialysis. But they can come to need such care more frequently than people who never formed a stone.

The message is obvious. Stone recurrence should be minimized through prevention efforts. Physicians who practice stone prevention need to measure eGFR appropriately, and if it begins to fall take proper steps to mitigate the causes of that fall.

Obstruction from stones always needs prompt, skilled, urological care that minimizes risk and trauma from surgery. Because silent obstruction can destroy a kidney, any symptoms that suggest new stone passage deserve urological attention.

High Blood Pressure

The NHANES and Olmsted County data show that a history of stones raises risk of elevated blood pressure. Loss of kidney function, even subtle, could raise blood pressure, and increased blood pressure can harm kidneys and reduce GFR. Unlike significant kidney disease, high blood pressure is easily treated to prevent strokes, heart disease, and kidney failure. But high blood pressure commonly escapes diagnosis and adequate treatment.

This means kidney stone prevention clinics are high blood pressure clinics, or at least a common place where high blood pressure can be first detected. All stone formers need to know their blood pressure and seek care if it is elevated.

Bottom Line

Stones are a painful and recurrent chronic disease that kidneys generally tolerate with at most a modest amount of injury and function loss. But compared to people without stones, those who make them have measurably increased risk of high blood pressure and loss of kidney function. Years of study have made clear that this disease demands attentive treatments aimed at prevention, and that surgeons who manage stones do everything possible to preserve kidney tissue.

132 Responses to “Kidney Stones, Kidney Function, Kidney Disease”

  1. Vera Love

    Hi I am 68 I had a kidney transplant 7 years ago I still have my original 2 kidneys. My question is, can “non functioning” kidneys develop stones?
    And side question, can Sarcoidosis cause, lead to, or mimic kidney failure or disease?

    Reply
    • Fredric L Coe

      Hi Vera Love, Yes; end stage kidneys can form stones, often poorly mineralized. An ultra low dose CT will reveal those with reasonable mineral content. Sarcoidosis can cause stones and renal failure, from elevated serum and/or urine calcium, and from direct disease within kidneys. I hope these answers are helpful, even if a bit tentative for lack of detailed information. Regards, Fred Coe

      Reply
  2. Elizabeth

    I am 58. I just had my 3rd kidney stone soundwave surgery. The 1st was 4 years ago and the 2nd a year ago. My stones tested to be calcium oxalate the first time. I still have smaller stones in both kidneys. I have developed osteoporosis in the past few years.

    I am changing to a low or no oxalate diet. What can I do to dissolve the smaller stones so they don’t get larger and have to do the soundwave surgery again? The surgery seems to be more painful and longer recovery each time.
    Thanks

    Reply
  3. Francis

    Hello Dr. I have been diagnosed of bladder and kidney stones. My two kidneys are having stones.
    Can all be removed together? What’s the best way of treating the stones? I’m afraid of undergoing an operation. Is there any alternative?

    Reply
    • Fredric L Coe

      Hi Francis, Your urologist will have to decide, but in general one would remove bladder and renal stones at one time if possible. The reason for the stones, and prevention of more is paramount. Here is a good primer of how to proceed. Above all, get the stones analysed! Regards, Fred Coe

      Reply
  4. Matthew

    Doctor,
    I had a two uric acid stones removed with laser lithotripsy. One was in my prostate, the other a 9mm stone in my left renal pelvis. I am obese. I have hypothyroidism and gout. My blood pressure is currently not high and I don’t yet show prediabetes.

    I am trying to understand so e things that have happened since the surgery, but I don’t yet have the vocabulary to discuss them.

    1. My ankles were swelling quite a bit prior to the kidney stone being removed. This subsided after the stone was removed.
    2. I was secreting an abnormal amount of sebum, or some other substance through my skin. My head was a greaseball. After my stones were removed, this was seriously reduced.
    3. The substance my skin was secreting would get in my eyes and leave them with a burning feeling. When I tasted it, it tasted very sharp. Almost like a lemon but not so pleasant. After the surgery, this stopped.
    4. My energy and alertness levels seem to be up after the surgery.

    I wouldn’t think this could’ve affected my physiology so radically, but it seems as. Where can I look to understand what has happened and why?

    Reply
  5. rahul tanwar

    My father 53 yrs old have stones in both the kidneys. GFR rate is 28ml/min for both kidneys combined. The uric acid is 6.9mg/do and creatinine is 6.9mg/dl. Doctor has mentioned that they will be operating in 2 days. He even mentioned about possibility of nephroctomy. Though he mentioned that they will be keeping a one month period before removing kidney. Is it possible to improve the functionality of kidney with stone removal?

    Reply
    • Fredric L Coe

      Hi Rahul, I do not have enough information to really help here. But if stones are obstructing his kidneys or causing infection their removal may well improve kidney function.I hope so. Regards, Fred Coe

      Reply
  6. Aditya

    Hi, my friend is 17 year old. He eats non veg to considerable extent. His uric acid is 7.5 mg/dL and urine analysis reveal calcium oxalate crystals (+) in urine but the creatinine is 0.88 mg/dL, eGFR is 121 ml/min, urine normal in colour and not experiencing any pain. Should ultrasound scan be considered to rule out the possibility of kidney stone ? What could be possible reasons for calcium oxalate in urine, is it only the non vegetarian food a contributing factor ? Can calcium oxalate crystal be formed in urine without kidney stones ? How seriously should be considered for a 17 year old.

    Reply
    • Fredric L Coe

      Hi Aditya, Such a high serum uric acid in a 17 year old is unusual and suggests such things as high blood pressure or disturbed renal function. Given the CaOx crystals his physicians may wish to measure 24 hour urine oxalate to be sure it is not high. His blood pressure would be of some import and can be measured at home with one of the many forearm digital machines now on the market. An ultra low dose CT can reveal stones far better than US and delivers very little radiation. His physicians may wish to consider it. Altogether it is the serum uric acid that most bothers me, and I am sure his physicians think the same. Regards, Fred Coe

      Reply
  7. Vj

    My friend has bilateral multiple renal stone. Now obstruction removed by stenting. But still stones are in kidney. Initially his creatinine 4.8 after stenting it reduced to 4.1. Any possibility of reduction in creatinine after removal of stone?

    Reply
    • Fredric L Coe

      Hi Vj, When the obstruction has been corrected the serum creatinine should fall to where it was before the obstruction. If that does not happen either the kidneys have been damaged by obstruction or there is another problem causing kidney disease. Primary hyperoxaluria or other very high oxalate conditions are always a worry in this kind of situation. I imagine his/her physicians are already looking at urine oxalate. There are other possibilities as well. Regards, Fred Coe

      Reply

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