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.

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

  1. Uthamanan Kuppusamy

    After stent installed for kidney stone..gfr is 60. Will it improve. Done after stone stuck at ureter.

    Reply
  2. Cristina

    Hello. I do have kidney stones and had surgery to blast them away several years ago. The stone was fragmented and not fully destroyed. I was not happy about the outcome. 4 years later I got Basic Metabolic panel and eGFR 60. I am 43 and waiting for a follow up at the end of the month. Should I be worried and if I remove any kidney stones will that improve my kidney function?

    Reply
    • Fredric L Coe, MD

      Hi Kristina, GFR will increase to the extent that it is being lowered by an obstructing stone. That it is so low means that both kidneys are involved, as obstructing only one kidney with the other one normal, gfr would be 80% or more of normal. So obstruction is the big worry and your urologist needs to minimize the length of the obstructed interval. Regards, Fred Coe

      Reply
  3. Anil

    I faced lithotripsy in 1995 PCNL in 2009 and now larg staghorne stone 3cm with multipls GFR 9.5%.
    Is it because of stone? Should I go for nephroctomy ? Right kidney is functioning 50%

    Reply
    • Fredric L Coe, MD

      Hi Anil, I gather the kidney with the staghorn stone has 9.5% of function. The judgment about removal of the stone vs. kidney requires an assessment of the radiographic images – is there functioning kidney but obstruction is impairing function, or is there just little remaining kidney tissue. Your surgeon makes that judgment. Regards, Fred Coe

      Reply
  4. Martha Doty

    I have a question. I have had chronic stones since I was 21, for the past 30 years. I currently have them bilaterally, and am passing one on the left which has a uretal stricture, and a larger stone of 4mm on the right. My GFR dropped from 87 to 51 in early August and has stayed no higher than 58. I am achy, itchy, hurting, and wondering if the GFR drop is part of the reason. Should I be concerned about a further drop? I have systemic lupus as well. Thank you!

    Reply
  5. Joni

    How common is it for a person’s kidney to completely fail from a large kidney stone? My sister has very severe MS and lost most of her feeling from her waste down, so last year her urologist diagnosed her with a large kidney stone. Since she could not feel it, the Urologist was fine with letting it be. So now we fast forward to this year, and her kidney has lost 100% of its functioning, she’s been in and out of the hospital with infections, near death, and they are just now deciding to take out that kidney completely since all function is gone. She is only 41 and living in a nursing home. Her quality of life is so low anyway. We are just so upset about this. I don’t understand why a urologist would let a person with neurological problems continue on with such a large stone to the point they lose a kidney.

    Reply
    • Fredric L Coe, MD

      Dear Joni, I am afraid it is not rare. Large stones obstruct the kidney and obstruction can destroy that kidney. I imagine her physicians felt the surgery was excessive given her general state, but a common outcome is sepsis from the obstructed kidney as I imagine happened here. At this stage removal is more or less necessary. Stones in her remaining kidney need care, because it will be her sole renal support. Regards, Fred Coe

      Reply
  6. Heidi

    My daughter has had trouble with filtration since she was young. She’s 24 and has had many stones and stents. Her Dr prolonged her getting one stone removed and I fear this has done damage. Now she has more stones now causing Low kidney functioning and alot of blood in her urine and it’s Friday. They put off helping her. She was told to go to the ER if she sees blood. No call back from urology. Please advise. She’s not feeling well at all

    Reply
    • Fredric L Coe, MD

      Hi Heidi, It sounds like your daughter has lost some kidney function because of obstruction from stones. That is unfortunate. Protecting her kidneys against obstruction is a main role for her urological surgeons, and if they are having difficulties in doing this they might want to help her find additional help at a kidney stone center – usually in medical school hospitals. It soulds like that may be the case, and that additional consultation is important. Regards, Fred Coe

      Reply

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