Latest / Common Sense Health / Kidneys Aren't Just Plumbing: Here's What They Really Do
Transcript
- Stephen: Hello. Most people think the kidneys are basically fancy plumbing. They make urine. You go to the toilet and that's it. So job is done. But that is a bit like saying the brain is just a lump that stops your hat falling down. Technically there is some anatomy involved, but we are missing quite a lot of the story. The kidneys are not simply urine making organs. They are involved in blood pressure control, fluid balance, electrolyte regulation, acid base balance, hormone production, red blood cell production, vitamin deactivation, toxin clearance, and even glucose production during fasting. And what have the kidneys ever done for us? But anyway, they do make urine. That's true. But urine is really just the product of this much bigger set of jobs. Every day your kidneys filter huge amounts of blood. They decide what to keep, what to remove and how much sodium to hold on to, how much potassium to get rid of, whether you need more or less water, whether your blood is becoming too acidic and whether your blood pressure needs adjusting. They are constantly working in the background doing a kind of biochemical administration job that nobody notices until the office catches fire. And this is where blood testing can become a little bit misleading. I'm not trying to scaremonger, but when people have kidney function checked, the usual markers are things like creatinine and EGFR. Creatinine is a waste product that comes largely from muscle metabolism, and EGFR is an estimated glomerular filtration rate. In simple terms, EGFR is an estimate of how well your kidneys are filtering your blood. Now, that sounds straightforward. If the kidney blood is normal, the kidneys must be fine. But that's not necessarily true. One of the really important things to understand is that we have two kidneys and they have quite a lot of spare capacity. If one kidney is healthy while the other kidney is declining, the healthier kidney can actually compensate. It can work harder, filter more and keep the overall blood result looking fairly normal. So if one kidney is doing a brilliant job and the other is quietly struggling, sadly the standard blood test may not clearly show that problem. The lab result is usually showing you the combined performance of both kidneys. It is not always telling you how each individual kidney is doing. So that means a person could have a problem affecting one kidney, such as scarring or reduced blood supply, obstruction, reflux damage, stones, structural abnormalities. And yet their blood tests may look still surprisingly reassuring. This is not because the because the blood test is useless. It is because the body is clever. ⁓ Clever compensation can hide this decline. This is especially true in the earlier stages. Kidney disease can be very quiet. It does not always announce itself with dramatic symptoms. Often there is no pain, no obvious change in urination and no clear sign that anything is wrong. By the time creatinine rises significantly or eGFR drops clearly, may already have been a meaningful loss of kidney function. Trends matter a single blood test can be useful, but it is only a snapshot What you really want to know is whether someone's kidney markers are stable over time Improving or gradually drifting in the wrong direction And when assessing eGFR from bloods, it is also worth mentioning cystatin C You creatinine based eGFR can be affected by muscle mass, diet, body size ethnic background, age, sex and protein intake Someone with more muscle mass may naturally produce more creatinine. Someone eating a low-carb ketogenic or carnivore diet may also need their blood results interpreted in the context because diet and body composition can influence some of the markers. So this is why interpreting bloods in the context of a carnivore or ketogenic way of eating is really crucial. Cystatin C tends to be a more accurate marker for estimating your kidney function because it is less influenced by muscle mass and the protein intake, then the creatinine test. It is not perfect because no test is perfect, but it can be very useful as an additional marker when you want a clearer picture. So if someone is concerned about kidney function, especially if their creatinine looks a bit confusing, cystatin C can be worth discussing with your doctor or clinician. But blood tests are only one part of the picture. Urine testing can be incredibly useful too. One of the early signs that the kidney filters are under stress is protein leaking into the urine. In particular, albumin in the urine can be an early warning sign of kidney damage, especially in people with diabetes or high blood pressure or metabolic syndrome. A urine albumin to creatinine ratio, often called ACR, can pick up signs of kidney stress that may not be obvious on a standard blood test. Foamy urine can sometimes be a clue that protein is present, although it is not diagnostic on its own. Blood in the urine, in urine volume, waking up frequently at night to pass urine, pain when passing urine, or changes in urinary flow can all be relevant. Some of it is explainable as well. a problem. Now again, none of these symptoms automatically means kidney disease, but they are part of the wider picture. And then there is blood pressure. The kidneys and blood pressure are deeply connected. The kidneys help regulate blood pressure through sodium balance, fluid balance, and hormonal systems such as the renin angiotensin-aldosterone system. High blood pressure can damage the kidneys and damage kidneys can worsen blood pressure. So you end up with a very unhelpful biological game of tennis where each side keeps trying to smash the ball back harder. This is why blood pressure should not be ignored when thinking about kidney health. If someone has persistently high blood pressure, it is worth asking whether they are carbohydrate intolerant or they're having too many carbs. Is their kidney involvement? Is their sleep apnea? Is their excess alcohol? Is their chronic stress? Is their medication contributing? Is there an issue with sodium and fluid handling? You see, you just need a lot of joined up thinking. The kidney is not separate from the rest of the body. It's plugged into metabolism. It's plugged into blood pressure, vascular health, hormones and inflammation. Now, another symptom people often ask about is flank pain. The kidneys sit towards the back of the body, either side of the spine underneath the lower ribs. Pain in that area is often described as flank pain. Kidney related flank pain can happen. with kidney stones or infection, some sort of obstruction, swelling, trauma or sometimes cysts. It may be dull and persistent or it may be severe and colicky, especially with stones. Anyone who has had a kidney stone will usually describe the pain in a way that makes you feel grateful for every boring day you have ever had. But it is important to be sensible here. Not all back pain is kidney pain. Muscles, ribs, discs, nerves and posture can all cause pain in the area but persistent flank pain especially if it comes with fever, vomiting or blood in the urine, pain passing urine or feeling very unwell should be taken pretty seriously. So ⁓ kidney infections can also become serious very quickly. Stones can obstruct the urine flow, blood in the urine needs proper assessment. so many things. So flank pain is not something to panic about but it is also not something to ignore if it is persistent severe. or comes with other symptoms. Swelling can also be a clue. If the kidneys are struggling to manage fluid and sodium properly, well fluid can accumulate. This may show up as swelling in the ankles or the feet or the hands or around the eyes. Some people may notice puffiness in the face, especially in the morning. And fatigue can also occur, particularly when kidney dysfunction affects a reflopoietin production. ⁓ EPO is what it's called, for short, is a hormone made by the kidneys that tells the bone marrow to produce red blood cells. If the kidneys are not producing enough EPO, anemia can develop. That can lead to fatigue, breathlessness, weakness, and poor exercise tolerance. And this is another example of why the kidneys are not just urine organs. They are involved in oxygen transport because they influence red blood cell production. They are involved in bone health because they activate vitamin D. They are involved in cardiovascular health because they regulate blood pressure and fluid balance. And they're involved in mineral balance because they handle calcium, phosphate, sodium, potassium and magnesium. They're involved in acid based balance because they help regulate blood pH. So when kidney health declines, the effects can be wide ranging. Now, if we're talking about chronic kidney disease, have to talk about type 2 diabetes because type 2 diabetes is one of the biggest drivers of kidney disease worldwide. And if we strip it right back, diabetes is a condition of chronically elevated blood glucose or what we call carbohydrate intolerance. Over time, persistently elevated glucose levels, they damage small blood vessels and the kidneys are full of tiny, delicate filtering structures that depend on a healthy The filtering units of the kidneys are called nephrons. Within these nephrons are glomeruli, which is Latin for a ball of yarn, and tiny filtration structures. These structures are not designed to be battered year after year, but high glucose and high insulin and inflammation and oxidative stress and glycation and high blood pressure, eventually damage is going to occur and protein may start leaking into the urine and blood pressure may rise. filtration may become abnormal. Now at first, the kidneys may actually hyper filter, meaning they work harder and filter more than they should. And this can make the numbers look deceptively acceptable for a while, but over time, that extra pressure can become damaging. And this is why metabolic health is kidney health. If someone has type two diabetes or pre-diabetes or central obesity or high blood pressure, fatty liver, high triglycerides or a long history of high sugar intake, the kidneys deserve attention long before anything dramatic happens. Now the good news is that improving metabolic health can make a major difference. Reducing chronically high blood glucose, lowering insulin demand, improving blood pressure, reducing visceral fat, improving inflammatory markers and removing the constant dietary assault of processed carbs and sugar. ⁓ can all support kidney health. And this is where a low carb or ketogenic or carnivore approach can be very powerful for some people, especially when it helps reverse type 2 diabetes or dramatically improve blood glucose control. But again, blood results need to be interpreted in context. If someone is eating more protein or has more muscle or has changed their diet substantially, creatinine and urea may need a more thoughtful interpretation rather than the sort of usual knee jerk. reaction. That does not mean dismiss kidney markers. It means understand them properly. Sugar and fructose are also worth mentioning here by the way. High intakes of sugar, from processed foods or fizzy drinks, fruit juices, sweets, desserts and ultra processed foods are not kind to metabolic health. Fructose is particularly interesting because it is handled differently from glucose. It is largely processed by the liver and can contribute to what people call insulin resistance. It can definitely contribute to fatty liver, raised triglycerides, uric acid production and metabolic dysfunction, certainly when it's consumed in high amounts, especially in refined or liquid forms. This does not mean a few berries are the same thing as drinking a litre of fizzy drink. They're not. But large amounts of sugar and fructose, especially in liquid form, can be a serious problem. And fruit juice is a classic example. It does have this health halo, but ⁓ Metabolically it can behave much like a soft drink. Now you can consume the sugar from several pieces of fruit in a few seconds, especially without the fibre. ⁓ Chewing and satiety that would normally slow things down if you're having actual fruit. Now if type 2 diabetes and metabolic dysfunction are major drivers of kidney disease, then reducing sugar and refined carbohydrate intake is not a side issue, it's central. And then there's a simple thing like water. And this is where we need a bit of common sense. People are often told to drink more water as though the human body is a house plant. dehydration is not good. Severe dehydration can definitely stress the kidneys. If someone is sweating heavily, exercising unwell or in a hot climate, fluid intake does matter. But that does not mean everyone should force down huge amounts of plain water all day. Overdoing plain water can dilute sodium levels, especially if someone is also eating very low salt or sweating a lot or following generic advice without considering electrolytes. Now, in extreme cases, excessive water intake can contribute to hyponatremia, which means low sodium in the blood. And that can be dangerous. The body regulates fluid and electrolytes together. Water does not work alone. Sodium, potassium, magnesium, hormones, kidney functions, blood pressure, diet and activity level, all matter. So the practical message is not drink as much water as possible. The practical message is drink appropriately. Use thirst as a guide and look at context. If you are exercising and sweating, eating low carb or in hot weather, you may need more fluid and more electrolytes, normally in the form of salt. The easiest thing to do is to add it just to mineral water. Now, if you're sitting at a desk school day or... doing what I'm doing sort of thing. Forced drinking water until your urine is completely clear may not be doing you any favors. Pale, straw-coloured urine is often a reasonable sign of hydration. Completely clear urine all day may suggest you're actually overdoing the water. Although context again always matters. For people eating ketogenic or carnival diets, electrolytes and particularly important ⁓ factor is because lower insulin levels can increase sodium loss through the kidneys. And that is one reason why people can feel weak or dizzy or headache or washed out when they first reduce carbohydrates, unless they pay attention to salt and minerals. again, context matters. Now when bloods and symptoms do not give the full answer, then imaging can also be helpful. A standard blood test tells you about overall function. know, imaging can show structure, obstruction, stones, cysts, scarring, kidney size, blood flow and whether one kidney looks different from the other. Ultrasound is often the first line imaging testing route. is non-invasive, does not involve radiation, can show kidney size, the shape, cysts, obvious blockages, swelling of the drainage system, and sometimes even stones. It can also show if one kidney is much smaller than the other, which may suggest an old injury or scarring, reduced blood supply, or even long-standing damage. ultrasound is useful but again it's not perfect but it does give you structural information but not always the detailed functional information. Now a CT scan gives much more detailed anatomical information. It can be very useful for stones and masses and trauma obstruction and complex anatomy. Some CT scans use contrast dye, which helps highlight blood vessels and tissues, but contrast does need some caution in people with reduced kidney function, for instance. So kidney markers are usually checked before any contrast is given, other problems with contrast. MRI can also be used in some kidney It gives excellent soft tissue detail and does not use ionizing radiation. Some MRI scans use ⁓ gadolinium-based contrast, also requires caution in advanced kidney disease, although the risk depends on the type of contrast and the person's kidney function. And then there are nuclear medicine scans, which can be reasonably... ⁓ sorry, not reasonably, but especially useful when you want to know how much each kidney is contributing. Now this is very relevant to the point about one kidney compensating for the other, which we mentioned at the beginning. A scan that assesses split kidney function can show whether one kidney is doing 50 % of the work and the other is doing the remaining 50%, or whether one is doing far more and the other far less. That is something a standard blood test may not reveal. So Imaging can answer a different question. Blood tests may tell you how your kidneys are doing overall, but imaging may help answer what does each kidney look like? Or is one kidney blocked, scarred, or smaller, swollen, or contributing less function than the other? Now, that difference does matter because if one kidney is declining and the other one is compensating, the overall blood result can look acceptable, like I say, until the reserve capacity starts to be reduced. This is why it's so important not to rely on one marker in isolation. Kidney health should be looked at through several lenses. Blood tests including creatinine, EGFR and ideally cystatine C where appropriate. Urine tests especially albumin to creatinine ratio. A monitoring of your blood pressure is a good idea and blood glucose and insulin resistant markers. Not a big fan of insulin resistance but fasted insulin is a good test. Symptoms such as flank pain or swelling, changes in urination, fatigue, blood in urine or recurrent infections should all be checked and imaging where the clinical picture suggests it is needed. No single test tells the whole story. The body is not a spreadsheet, even though sometimes clinicians try very hard to make it one. The big practical takeaways are fairly simple. Do not assume normal bloods always mean perfect kidney health, especially if symptoms are or if there is a reason to suspect one-sided kidney disease. Pay attention to blood pressure because it is both a cause and a consequence of kidney problems and if you have type 2 diabetes or pre-diabetes as it's known or carbohydrate intolerance, take kidney monitoring seriously. Avoid high intakes of sugar and fructose especially from processed foods and sweet fizzy drinks. Do not force excessive amounts of plain water just because someone on the internet told you that your urine must look like Evian. Hydrate sensibly and remember that electrolytes matter. Ask about urine testing, not just blood testing. Consider cystatin C if creatinine based EGFR does not seem to fit the bill and if there are symptoms like I say such as persistent flank pain, blood in urine or recurrent urinary infections unexplained swelling or changes in urination, do not just shrug because the blood test looks normal. The kidneys are quiet workers. They do not usually complain early. They compensate, adapt, and keep going, which is wonderful, until it becomes the reason we miss something important. So the aim is not to become anxious about every lab result or every twinge in the back. The aim is to be awake to the bigger picture. Kidney health is metabolic health, vascular health. blood pressure, health, hormonal health and electrolyte health all rolled into two small organs sitting quietly at the back of your abdomen. They are not glamorous. They are not trendy. Nobody's on Instagram flexing their kidneys. But they are doing extraordinary work every minute of every day. And if one of them starts struggling, the other one may heroically cover for it for a long time. That is impressive biology. But it is also why we need to look beyond the basics and think properly.