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As a naturopathic doctor with a practice focusing on kidney health, I am often called upon by other holistic practitioners to collaborate with the renal issues of their patients' care. The first question most practitioners have is does the patient actually have a kidney issue?" There can often be a fine line between a healthy kidney and a kidney we need to be concerned about. Once we've identified that there is a problem, how can we support a compromised kidney?
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Most people use the eGFR number to gauge the percentage of renal function, but it is good to know how this number is arrived at and why it does not apply to all patients equally. The eGFR is a derived number that comes from plugging four values into a formula. Those four values are creatinine, age, gender, and race. Most labs will automatically calculate eGFR with the metabolic panel, but if it is not listed one can go to the National Kidney Foundation page for kidney professionals to calculate a patient's eGFR at https://www.kidney.org/professionals/KDOQI/gfr_calculator. This guide will also indicate if a referral to a nephrologist is warranted.
As age is part of the calculation of eGFR, the formula does not work well for the very young and the very old. Using this formula, a 70-year-old white male with an acceptable creatinine of 1.3, would have an eGFR of 55. While some loss of filtration is part of aging, this would not be a pathology. Traditional Chinese medicine would call it a loss of jing. Many elderly patients become needlessly panicked looking at their eGFR on a blood test, as it will always be low with the elderly. They might also become stressed when some labs use 1.0 at the high end of normal for creatinine, instead of 1.3. While they would benefit from a kidney-friendly diet and lifestyle, if the creatinine is under 1.3, it is within an acceptable range.
Even if the creatinine is elevated in the elderly, the first question I ask is how well hydrated were they at the time of the blood draw. As creatinine is measured per volume unit of blood, dehydration will cause the creatinine to be more concentrated in the urine.1 Proper hydration may be an ongoing struggle with older patients. Sometimes with a retest after good hydration we can shave off several tenths of a point off the serum creatinine.
After inquiring about hydration, the next question I ask is how is the blood pressure running. Filtration within the kidney takes place across a pressure gradient, just as the more one squeezes a sponge the better it cleans. The kidney's natural tendency is that when the filtration is low, the blood pressure goes up. However, if the blood pressure is very low, whether due to over correction with medication, shock, or adrenal insufficiency, this can raise creatinine.2 In practice, a patient with a creatinine of 8.0 would seem to be headed straight for dialysis. However, this patient's blood pressure was 90/60. Raising his blood pressure, the creatinine came down to 6.0. This is not a miracle by any means, but enough to delay dialysis several months.
Besides the elderly, very fit men may run a high creatinine. As creatinine is a breakdown product for muscle tissue, increased muscle mass will cause a higher baseline creatinine. Creatinine may be as high as 1.6 in a fit young man without indicating renal pathology. When in doubt, the blood test Cystatin C can be used as an alternative to creatinine. Cystatin C is not dependent on muscle mass like creatinine, and it can be used to calculate eGFR.3
Along with high creatinine, there are usually other indicators that may be off with progressed kidney disease. If one suspects kidney problems, there is usually a predictable pattern or some reason why the patient is not presenting typically. One should expect to see an elevation of BUN, as BUN and creatinine tend to track together. BUN comes from dietary protein, and it will be a direct indicator of how much protein the patient has recently ingested. As such it is more variable than creatinine. Dietary protein may go up and down, but muscle mass is relatively constant. A high BUN without any other indicator of kidney weakness is due to a high protein diet. A high creatinine with a low BUN is probably due to the patient going to an extreme cutting out protein in the diet. The BUN/creatinine ratio is often listed on the metabolic panel. Normal range is generally 10 to 20, and creatinine should track with BUN as it requires protein to maintain muscle mass. If the patient has a very high or a very low ratio, it's good to find out why.
Besides high BUN, there may be renal anemia due to a lack of erythropoietin. This will show with a low hemoglobin, hematocrit, and RBC. However, this only happens with advanced kidney disease after the creatinine has started to rise. If anemia occurs before this, suspect another cause. It is worth noting that dehydration will cause an elevation of hemoglobin and hematocrit, so the renal anemia may not be initially apparent.4 It's good to note if there is a high or low MCV or an elevated RDW, to see if the patient is in need of B12 or iron. It may also be useful to run an iron panel, particularly if the patient has cut out all animal protein.
Another indicator with advanced kidney disease is an elevation of potassium. While healthy kidneys expel potassium in the urine, a very weak kidney is not able to do this, and potassium will rise. This may not be the case however, if the patient is consuming foods of low nutritional value and just doesn't have much potassium intake. Potassium sparing diuretics can also throw this number off. Surprisingly sodium usually stays in homeostasis as the body tightly regulates it. Sodium may even run low if there are adrenal or thyroid issues.
As the kidneys regulate the blood pH, expect to see indicators of renal acidosis. One should also expect to see a low CO2 level as the body becomes too acidic and the lungs try to compensate by expelling carbon dioxide. The kidneys maintain alkalinity of the blood by expelling metabolic acids in the urine. A urinary pH of 6.5 to 5.5 generally indicates that the kidneys are keeping up with this function. With advanced kidney disease, the kidneys are no longer maintaining the pH, and the urine will have a pH closer to 7.0. The patient is mostly passing water with the urine and acidic wastes are not being properly filtered out. (Extreme protein deprivation or extreme water intake may also cause a neutral urinary pH.5)
With kidney trouble, expect to see a high blood pressure or a highly variable blood pressure. When the whole mechanism of blood pressure control is damaged in advanced renal disease, hypertension can be difficult to manage. Frequent checking at different times and in different settings is useful to see a pattern. The patient who is very troubled with their health concerns may have sympathetic dominance and white coat" hypertension. It's helpful for the patient to have a self-inflating blood pressure monitor and keep their own log. (In practice, the units with a forearm cuff have appeared more reliable than those that attach at the wrist.)
Although these other indicators reinforce the seriousness of the patient's condition, the primary indicator is creatinine. When creatinine does rise, it often catches patients by surprise. Patients often tend to attribute this rise to some condition in the recent past and expect a quick fix. But usually the conditions were building for years, if not decades before trouble was apparent.
Most young adults start out with approximately 1 million nephrons in each kidney. Starting as early as age 18, these filtering units break down as part of normal aging. People may lose as much as 1% of their total nephrons in a single year. Usually this is not a problem as we have reserves in our kidney. But if there is a disease process causing progressive damage to the kidneys, this loss is accelerated. In the initial stages this isn't a problem. Some of the nephrons are lost, and the remaining functional nephrons just work harder to keep up with the demands of the body. This is a kidney in a state of hyperfiltration, with fewer and fewer nephrons working overtime.6 This state can go on for years, and normal creatinine is maintained. There's no indication on the blood test that the kidneys are working hard to maintain filtration and keep up this creatinine.
Eventually the kidneys reach a point where they can't work any harder and the creatinine goes up. This may happen incrementally with the creatinine inching up a tenth of a point at a time or it may be a sudden jump. Patients may be in denial about the seriousness of the condition. They may have experienced acute kidney stress or dehydration that elevated the creatinine and, once the situation was addressed, the creatinine returned to its normal baseline. Now, they expect that once this situation is addressed that the kidneys will once again return to normal.
Some patients fail to grasp the progressive nature of chronic kidney disease. FSGS, focal segmental glomerulosclerosis, is a particularly difficult degenerative condition of the kidneys. A patient with FSGS asked me to uncover the cause of her high creatinine. Why would a patient with the most deadly form of nephrotic syndrome be asking this? She had had FSGS for 10 years and to her thinking it was okay; the creatinine was always normal, and her life was unaffected. No one had explained that the kidneys were not all right, and for 10 years there was a gradual, insidious breakdown of kidney tissue.
Once there is a critical loss in the number of functional glomeruli, histopathological changes take place, and the kidneys become scarred as excessive demands are placed on them.7 Proteinuria is a hallmark of all types of nephrotic syndrome such as IgA nephropathy, FSGS, and lupus nephritis. But as the kidneys are damaged, even diabetic nephropathy and hypertensive damage will show some proteinuria as the kidney loses structural integrity.8 Cardiovascular stress will also start to become a long-term concern.
Besides chronic kidney disease, other conditions can put the kidneys in a state of hyperfiltration. Age-related kidney decline can happen in the absence of any pathology, with more nephrologists looking toward conservative care rather than dialysis for life extension.9 Morbid obesity can also put the kidneys into a chronically overworked state of hyperfiltration. Although more muscle mass produces more creatinine, all metabolically active tissue produces wastes that must be handled by the kidneys. Hyperfiltration can also be the result of congenitally small kidneys or a low birth weight.10 Another group facing hyperfiltration is kidney transplant donors. With a reduced number of glomeruli, supporting their single kidney becomes important.11
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