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.

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

  1. Moheb

    Forget to mention I am 38 years old

    Reply
  2. Moheb

    Hi,
    I have been complaining for burning after urinating for some time. And I develop sand stones frequently the first ones were 4 years back and then every 3 months I do have the same condition sometimes they are oxalate and sometimes are uric acid. Last blood test showed eGFR 84 and creatinine 1.11 . Doctor said no problem as long as no protein or there are no clues in the urine and blood tests for CKD. There is hameturia from time to time around where the numbers around 50 but the microscopic results shows negative WBC or RBC.
    I forget to mention I did US and CT before and only tiny sand stones are found.
    Should I worry about my kidney and how can I prevent recurring stones?
    Thanks

    Reply
  3. Lynne

    Hi,
    I am a 55 year old, white, female and was experiencing right side pain which sent me to the ER. My metabolic panel showed the following and I am wondering if this is a cause for concern?
    BUN-12
    Creatinine-1.07
    BUN/Creatinine Ratio-11
    GFR- 57
    Had a renal catscan which showed
    “Imaging through the left kidney reveals possible mild dilatation of the lower pole collecting system. There may also be a slightly prominent extrarenal pelvis on the left. There is no evidence for renal mass or calculus on the left side.”
    Have had two dilation’s done for urethral stricture was having difficulty starting a stream, spraying, straining. Procedures helped and am much better in that area. I thank you for your time.

    Reply
    • Fredric L Coe

      Hi Lynne, I am not clear if you have stones or not. The CT seems to show no stones, but does show dilation of a lower pole collecting system. This is not clear to me, but perhaps your urologist understands it. Your pain was right sided but there is no mention of the right kidney on CT. Urethral stricture will not cause your reduced eGFR (57). The cause of the right sided pain seems unknown. I guess I would want to know what caused the pain, and why your eGFR is reduced – high blood pressure, diabetes, other? Regards, Fred Coe

      Reply
  4. Genevieve Rosewood

    Hello – My Creatinine Serum Clearance is 61.31, have had two episodes with kidney stones about 10 years ago and past them successfully. Having middle lower right back pain for a few months now and wondering if there is an obstruction. Am female, 69 years old. Do you think it’s time to see a doctor? Thank you.

    Reply
    • Fredric L Coe

      Hi Genevieve, The value you quote is estimated GFR (eGFR) calculated from your serum creatinine, and your value is just at the border of stage 2 and stage 3a chronic kidney disease. But in fact, millions of people are being labeled as chronic kidney disease by this calculation and almost all are simply older with older kidneys and not kidney disease if by disease we mean an abnormality from the expected course of aging. Even so, if you have had stones and you have pain suggesting a stone, obstruction is possible and it is essential your physician determine this. So please bring yourself to your physician and let her/him decide if things are abnormal or not in your urinary tract. Regards, Fred Coe

      Reply
  5. Steve

    I have Wegeners desease and Sjogrens syndrome. Have frequent stone blockage. They are 90% phosphate stones. My average gfr over the past year is around 48% but have dipped in the low 30’s during stone occurrences. I have never passed one as they have always been surgically removed but was wondering if I could try or is it too dangerous to have blockage for that long with already reduced kidney function. Just hate having all these lithotripsy procedures.

    Reply
    • Fredric L Coe

      Hi Steve, Given your underlying diseases, renal tubular acidosis does seem very likely. Kidney function loss may well be worsened by the phosphate crystallization. As for letting stones block your kidneys, it would be very unwise. Prevention of stones from acquired RTA is no small matter, and no trials exist given the small numbers of patients. This article gives a lot of background about RTA and also about ways to reduce stones. High fluids, and perhaps a thiazide type diuretic like chlorthalidone + potassium chloride to replete potassium losses might help. This is complex medicine, and your physicians no doubt realize that. Regards, Fred Coe

      Reply
  6. 133odete

    I’m 30 years old and my GFR is very low for my age, only 73 mL/min/1,73 m² but I don’t have any other disease associated like diabetis or high pressure. Ultrassound detected a small stone of 2.8 mm in the lower part of the kidney and nothing else abnormal. The stone never caused me any pain and I just discover its presence by the ultrassound. Sodium and potassium are in normal rate in blood and the urine test did not show the presence of protein. What can be causing my GFR to be so low? Also I don’t remember of having any urine infection. Help me please, I’ve been concerned about it for more than a year.

    Reply
    • Fredric L Coe

      Hi 133odete, Your situation is complex: reduced calculated GFR using serum creatinine, no urine protein excess, and a small stone in one kidney by ultra sound with, I presume, normal size kidneys with normal tissue density. The latter two points are important. Blood pressure is normal, no diabetes. I would think you should have a nephrologist as one of your physicians, so she/he can sort this out. Possibly, serum creatinine is not a good marker for your GFR as some people do not secrete it and their blood values give false estimates. Possibly your kidney size or density on US are not normal. Possibly you have some cause of stones that is also a cause of kidney disease such as a very high urine oxalate level – 24 hour urine testing can tell this. A renal specialist is trained to get your answer, and I would urge you get one. Regards, Fred Coe

      Reply
      • 133odete

        The US showed that my kidneys are in normal size and density. Also I already saw a nephrologist that ordered a creatinine clearance that showed the result of 73 mL/min/1,73 m². Probably my problem is high urine oxalate as you said and my nephrologist has already ordered a 24 hour urine testing to see the oxalate levels. Also I had already found some oxalate crystals in previous urine testing that I made in the past. So I think you may be right. Another question: can bowel problems as gluten sensivity cause oxalate to raise in urine? Assuming it’s a bowel problem with no other problem associated, can I revert the situation improving my bowel and raise my GFR again?

        Reply
        • Fredric L Coe

          Hi 133odete, If your urine oxalate is high, and high enough to have injured your kidneys the problem is very significant. Bowel disease can raise urine oxalate if you have true gluten enteropathy. The problem with oxalate induced kidney disease is that lost function does not always return as fully as one would hope. So discovery and reduction of urine oxalate is imperative. Regards, Fred Coe

          Reply
  7. Nisar

    Sir iam 22 iwas diagnosed with kidney stones 3 years back now also 5 mm 6mm stone’s creatinine level is 1.5
    My doctor says it is normal it is due to stones shall i believe him

    Reply
    • Fredric L Coe

      Hi Nisar, Your serum creatinine is high and that may reflect obstruction by a stone. I imagine your urologist has checked for this, which is very important. If there is no obstruction, your physician should consider causes of stones that also cause reduced kidney function. The most important of these is primary hyperoxaluria that is detected from the 24 hour urine. The other causes are numerous and your physician knows them and can determine if any are present. Your physician knows you case and I do not. Possibly you have recently passed a stone, or had surgery or shock wave treatment or infection, and any of these can lower kidney function briefly. If that is the case, your creatinine will fall to normal. Regards, Fred Coe

      Reply
  8. Pete Lincoln

    I have 1 kidney having removed the right kidney due to RCC. Pathology reported I also had diabetic glomurosclerosis. After nephrectomy eGFR dropped from 73 to 36. A recent ultrasound detected a 7 mm stone in left kidney. It did not show up on presurgical FUB X-Ray (4 months ago) so my urologist says it does not require treatment. This sounds wrong. My nephrologist says its no concern because its enclosed within the parenchyma but this does not make much sense. My concern obviously is possible obstruction with only 1 kidney. That would not be good.

    My urine pH has been running 5.5-6 so I suspect its a uric acid stone which explains why it does not show on X-Ray.

    I also have proteinuria and a recent MRI says I have a number of tiny renal cysts but no mention of the stone, and perhaps neither is related to the stone. At 7 mm it was unlikely to have passed without my notice. I also have lower back/side pain that comes and goes and is not exercise related.

    If I understand your posts I should probably be dealing more aggressively with the stone and hopefully get some improvement or at least stability to renal function with removal and preventive treatment. May have to check with another urologist and run some of your stuff past him/her.

    Reply
    • Fredric L Coe

      Hi Pete, It sounds like diabetic kidney disease is a major issue for you, and your nephrologist is no doubt doing all she/he can to ward off further loss of function. In a diabetic with a stone like yours uric acid is a very high likelihood. Your physician can tell using the CT scan and measuring the radiographic density of the stone. Although potassium alkali may be limited from your reduced kidney disease and the effects of diabetes on renal potassium handling raising urine pH to dissolve uric acid and prevent stones and potential surgery are both important. I would ask your nephrologist about the matter. MRI will not show stones reliably. Regards, Fred Coe

      Reply
    • Fredric L Coe

      Hi Pete, It sounds like diabetic kidney disease is a major issue for you, and your nephrologist is no doubt doing all she/he can to ward off further loss of function. In a diabetic with a stone like yours uric acid is a very high likelihood. Your physician can tell using the CT scan and measuring the radiographic density of the stone. Although potassium alkali may be limited from your reduced kidney disease and the effects of diabetes on renal potassium handling raising urine pH to dissolve uric acid and prevent stones and potential surgery are both important. I would ask your nephrologist about the matter. MRI will not show stones reliably. Regards, Fred Coe

      Reply

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