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The kidneys play a vital role in clearing body wastes and maintaining body fluid levels. Therefore, it is essential to have knowledge about the causes of kidney damage and avoid those habits that can harm your kidneys, such as a lack of fluid intake or sleep.
Kidney Tests: Serum Creatinine and EGFR
The normal clearance of certain excess or potentially toxic elements from the body occurs within healthy kidney tissue. Under certain conditions, slowed or even absent clearance of these substances may result.
The rising levels of certain toxic molecules may cause a progressive lack of appetite, nausea, vomiting, itching, difficulty with thinking, coma, and even death. Although, a harmful condition, such as changes in the concentration of specific ions or even a buildup of fluid, may occur and lead to kidney malfunction or damage relatively quickly.
While there are exceptions, most situations in which the kidneys fail to function properly are not accompanied by a perceivable discomfort. So, in scenarios in which kidney dysfunction or damage is suspected, one must look for changes in certain laboratory tests.
One marker that can be measured to determine a person’s kidney filtration activity is the blood concentration of a substance called creatinine, the serum creatinine level.
In the setting of either an acute kidney injury (AKI), in which the kidney tissue has been recently impaired or damaged, (1) or a chronic kidney disease (CKD), in which permanent damage to kidney tissues has been established for a long time, (2) the serum creatinine level will usually be higher than expected.
This is because injured or damaged kidney structures, usually renal glomeruli, will less effectively remove creatinine from the blood, leading to a reduction in the creatinine clearance. Therefore, an increase in serum creatinine is almost always indicative of a reduction in the glomerular filtration rate (GFR).
Because this correlation is relatively strong, a variety of equations have been developed that utilize an individual’s serum creatinine level in addition to a few other individual characteristics to estimate GFR (eGFR).
Given that many situations may occur, which can lead to kidney injury and permanent kidney dysfunction, it is useful to discuss these conditions within a commonly used framework by physicians. The terms prerenal, intrinsic renal, and postrenal are used in the categorization of the various causes of kidney harm. (3)
A prerenal state is a condition in which kidney dysfunction has occurred because of inadequate blood flow to the kidney tissue.
Conditions in which kidney blood flow may become significantly reduced include those in which a significant amount of fluid has been lost from the body, such as:
- Copious skin losses (excessive sweating)
- Gastrointestinal losses (vomiting, diarrhea)
- Vascular losses (bleeding)
- Renal losses (excessive urination not occurring as a natural result of excessive fluid intake)
A prerenal state can also evolve rather quickly if normal water and salt intake are significantly restricted.
Symptoms and signs
Although the kidneys themselves will not necessarily cause pain in the setting of a prerenal state, warning signals that a prerenal state is present include:
- Feeling of lightheadedness or “feeling faint” (especially present when arising from a supine or seated position)
- Palpitations or a faster heart rate than usual
- An increased sense of thirst
- Drier than normal mucous membranes
- Diminished skin turgor
- Decreased urine output
- The production of a darker or more concentrated-appearing urine
Avoiding excessive fluid losses or a prolonged reduction in fluid intake is the best way to avoid a prerenal state.
Because the optimal fluid status of an individual may be highly variable and based on a number of preexisting health conditions, it is important to discuss this issue with a physician if the person is considering changing their present intake of water or salt.
It is vital to note that in some instances, a higher intake of fluid than is normally consumed may lead to very harmful consequences, including a dangerous imbalance of the blood’s sodium concentration, higher blood pressure, and congestive heart failure.
Overall, however, in most individuals, a prerenal state can be avoided successfully if activities that may be thought to enhance fluid losses are considered carefully prior to them occurring.
- For individuals who exercise vigorously or are to be exposed to conditions in which sweating may be significant, taking in extra water and salt prior to the fluid losses may mitigate entirely whatever change in kidney blood flow that may have otherwise occurred.
- During a prolonged activity in which fluid losses may occur at a higher rate than normal, drinking enough water accompanied by a small amount of salt or a balanced electrolyte beverage so that urination occurs at least every 2–3 hours can ensure in most cases that the overall fluid status of the body is being maintained.
If a person suspects they may be developing or have developed a prerenal state, quick fluid restoration is advised in most cases. (4)
In cases where oral restoration is not practically possible (such as when a person is vomiting), fluid replacement is best accomplished in the hospital setting under the guidance of medical experts using intravenous fluids.
However, it is important to note that water does not efficiently correct an underlying deficit in kidney blood flow. Instead, in most cases, a combination of water and salt is much more effective. An example of this occurs in cases of intravenous fluid administration.
In the home setting, taking enough fluid and salt (such as with salty foods including pickles, olives, and soups) to promote a higher blood pressure generally acts to correct a mild prerenal state.
Habits to avoid
- Performing an activity in which excessive fluid losses occur without replacing lost fluids quickly and adequately.
- Using only water (and not a combination of both water and salt) to correct a prerenal state.
- Continuing prescribed medications used to treat high blood pressure (hypertension) in a situation in which low blood pressure has newly occurred (as with many prerenal states). In such a situation, it may be wise (always with the specific guidance of a person’s physician) to consider a reduction in normally administered medications to allow critically low blood pressure to be avoided.
Intrinsic Renal Conditions
An intrinsic renal state is a condition in which kidney damage has occurred but not due to lack of adequate kidney blood flow (a prerenal state) or obstruction of urine outflow (a postrenal state).
As with both prerenal and postrenal conditions, an intrinsic renal state will eventually lead to a loss of GFR.
Intrinsic renal conditions are sub-categorized into those impacting primarily:
- The filters of the kidney (glomeruli)
- The blood vessels within the kidney (vasculature)
- The small tubes that connect the glomeruli to the area within the kidney that collects newly made urine (tubules)
- The space adjacent to the glomeruli, vasculature, and tubules within the kidney (interstitial space)
Many diseases can cause dysfunction and damage to any of the specific areas (glomeruli, vasculature, tubules, interstitial space) within the kidney.
These conditions may cause disease found in many other parts of the body, while others may be confined chiefly to the kidney tissue. These conditions may be:
- A result of a maladapted immune system
- A result of a renal adaptation to a systemic disease
- A result of toxic or even allergen exposure
Symptoms and signs
In cases in which an intrinsic renal condition may also impact parts of the body in addition to the kidney tissue, a multitude of symptoms or signs may develop, such as:
- Shortness of breath
- Chest discomfort
- Joint or muscle aches
- Changes in cognition
The symptoms or signs present in situations in which the kidney tissue is primarily affected may be profound or quite minimal initially. Many conditions in this category may be associated with either protein or blood in the urine. These can be readily detected with basic urine tests.
In many cases, an individual may note that the urine, even casually observed, may either contain excessive foam or bubbles (which may indicate the presence of excessive protein) or be very dark or “cola-colored” (which may indicate the presence of blood).
Although not especially common, some patients with certain intrinsic renal conditions may report the onset of flank pain.
In some cases of intrinsic renal damage, prevention is not practically possible. However, many actions that might lead to an intrinsic renal state can be avoided.
- Potentially harmful activities include the chronic or excessive use of certain potentially nephrotoxic agents. Common over-the-counter agents include nonsteroidal anti-inflammatory drugs (NSAIDs), proton pump inhibitors, and calcium supplements.
- The use of certain prescribed medications may also lead to nephrotoxicity, although harmful effects are not certain to occur in any specific individual.
- Medications that are associated with intrinsic renal AKI events include certain antimicrobial agents, chemotherapeutics, and iodinated radiocontrast agents.
In addition to the use or overuse of certain over-the-counter and prescribed drugs, smoking has been associated with the development of CKD and accelerates the progression of CKD once established. (5) Additionally, smoking cessation has been associated with a slower rate of CKD progression.
Specific actions that a person may actively take to prevent or slow the progression of a preexisting CKD include:
- Optimizing control of systemic diseases that may impact CKD (such as hypertension, diabetes mellitus, and obesity). (6)
- Controlling hyperuricemia or a high serum uric acid level, which can cause gout. Lowering uric acid to goal range (such as <7.0 mg/dL) has been shown to improve kidney prognosis. (7)
- Controlling metabolic acidosis, which is the presence of a low serum bicarbonate level that has occurred not in response to a low amount of dissolved CO2 in the blood.
- Modifying dietary protein to be approximately 0.6–0.8 g/kg/day. (8) Plant proteins are felt to be overall superior for kidney heath compared to animal proteins.
- Using certain medications in specific medical situations. Commonly used medications to reduce the progression of CKD include angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs).
Some specific causes of intrinsic renal states may be treated with specific medication, such as those that might target a component of the immune system that is acting to produce kidney damage.
In all cases, the management of either AKI or CKD arising from an intrinsic renal state involves ongoing surveillance, identification, and correction of a number of complications that may ensue with the progressive loss of kidney function. These include:
- Fluid overload
- High blood pressure
- High potassium concentration
- Metabolic acidosis
- High uric acid concentration
- Disorders related to calcium, phosphorus, vitamin D, and parathyroid hormone levels
Habits to avoid
- Chronically or excessively using any over-the-counter medication, which may be nephrotoxic, without physician guidance and kidney monitoring to ensure the ongoing safety
- Excessively consuming salt in the setting of poorly controlled blood pressure
- Excessively consuming sugar in the setting of poorly controlled diabetes mellitus
- Excessively consuming calories in the setting of obesity
- Excessively consuming foods or beverages that promote uric acid formation in the setting of hyperuricemia
- Excessively consuming protein (especially animal-derived) in the setting of CKD
A postrenal state is a condition in which kidney dysfunction or damage has occurred because of either an incomplete or complete blockage of the outflow of urine from either one or both kidneys.
As with both prerenal and intrinsic renal conditions, a postrenal state eventually leads to a loss of GFR.
Any process that impedes the outflow of urine from a kidney or kidneys causes a postrenal state. Common causes include:
- An obstructing kidney stone may commonly be located within the kidney or within the tube (ureter), connecting the kidney to the bladder.
- An obstructing tumor, such as might arise from the kidney, ureter, bladder, and structures adjacent to the ureters or bladder.
- Bladder dysfunction may occur as a result of medication side effects or neurologic dysfunction.
Symptoms and signs
- For patients with partial urine outflow obstruction of one or both kidneys, urine output may increase as a result of changes to the affected kidney’s ability to concentrate the urine it is producing.
- With complete urine obstruction of one kidney, overall urine output may not change as the contralateral, non-obstructed kidney will tend to produce a urine volume to maintain the body’s fluid equilibrium.
- With complete obstruction of both kidneys, urine output will cease entirely.
- In many (but not all) cases, flank pain will occur along with the postrenal state. Flank pain may range from mild to extreme, and radiation of the pain to the groin may also be present.
- Blood may be present in the urine, and it is sometimes frank (notable with only casual observation).
- In the setting of infection arising from the obstruction to urine outflow, additional symptoms and signs related to the infection may be present and include fever, chills, rigors, nausea, vomiting, and altered mentation.
In the case of an obstructing kidney stone, one goal that should be accomplished following the obstruction’s immediate treatment is to prevent the formation of future stones.
Additionally, a study of the urine to measure the various components that contribute to stone formation may also be helpful. (9)
In the cases of certain tumors, routine cancer surveillance, as indicated by practice guidelines, will tend to identify certain cancers earlier, thus decreasing the chance of tumor-related urine outflow obstruction.
For patients with abnormal urine frequency or the perception of incomplete bladder emptying following urination, an evaluation by a medical professional trained in such scenarios may more quickly identify and correct a problem before its evolution to cause the postrenal state.
As there are many different types of stones, there are different specific remedies to employ in the case of a postrenal state caused by a kidney stone.
Therefore, guidance from a trained expert in stone disease (usually a nephrologist or urologist) is crucial to quickly identify the correct dietary or medication solution to be initiated.
Generally, however, for stone formers without specific contraindications, increased fluid consumption is advised so that the overall concentrations of urine constituents, which may coalesce to form crystals, will be lowered, thus reducing the chance of stone formation.
For obstruction caused by other non-stone issues, cessation of the offending medication that has caused bladder dysfunction or treatment of ureteral compression via ureteral stenting may lead to quick restitution of relatively normal urine flow.
For tumor-related issues impacting urine outflow, targeted therapies to reduce tumor mass will help alleviate the situation.
Habits to avoid
- Ignoring thirst or consuming relatively little fluid chronically may lead to a relatively low fluid balance within the body and a relatively concentrated urine production. In some individuals, this situation may promote the formation of kidney stones.
- Ignoring a change in urine output without an obvious explanation. In certain situations, less urine output (or even more urine output) may result from urine outflow obstruction. An individual should promptly seek medical attention to have the postrenal state confirmed or ruled out.
- Ignoring a change in urination quality. As above, changes in urination quality may be a symptom of the postrenal state. A decreased urine stream, more frequent urination, and a sensation of incomplete bladder emptying may all be perceived with bladder dysfunction or bladder outflow compromise.
It is imperative to modify your lifestyle habits to preserve your kidney’s health, and thus your overall well-being. This is more so important with advancing age as the risks of kidney stones and damage increase in old age.