How can Doctors tell if one of your kidneys isn't working?

Submitted by FineLetMeSayIt t3_11a4rz2 in askscience

I tried to Google this and did not get any answers specific to this question. From what I understand, you really only need one kidney to survive. That's why live donors/recipients are a thing. Also, if you were born with two healthy kidneys one can pick up the slack of the other if something goes wrong. So will they only know you have a kidney problem when BOTH fail? I assume as long as one is functioning, your tests and blood work would come back normal.

EDIT: To piggyback this logic, why don't we have more 'spares' of other organs. Why is the redundancy factor only built into kidneys?

179

Comments

You must log in or register to comment.

lascivious_boasts t1_j9pxpbj wrote

The short answer is that you are correct. Routine tests, including the rate of urine production, the ability of the body to clear waste products (creatinine, eGFR, urea) may all be normal in the case of only a single kidney working.

It's not very rare to find someone with one kid ey by accident when doing a scan. These are caused by congenital issues that led to a solitary kidney or an issue in early childhood that damaged one kidney and not the other.

Occasionally there will be mild derangement of some of those values that lead to the suspicion that a single kidney is not working and the other is working much better.

In this case there are some tests that can be used. As one of the main reasons for kidneys to fail is blockages in the arteries that feed blood into them, an arteriogram can show if one kidney is getting blood while the other isn't. This can be done with an intravascular catheter, but is more commonly done with CT and arterial phase contrast. If one kidney is getting lots of blood, and something is blocking the artery to the other (renal artery stenosis) then it's a fair bet that the one not getting blood isn't working well.

Equally, structural differences can show if there is a blockage in the outflow of one kidney and not the other (unilateral hydronephrosis, where the kidney retains urine due to the pressure needed to push it through a narrow ureter).

Finally, the test that really shows this is a differential renal function test. This can be done in a variety of ways. One includes injecting a dye and seeing how much comes out of each kidney by CT scanning and looking at how much dye is in each kidney. Another involves the differential clearance of a radioactive marker.

As to why we have two of some organs and one of others: it's just evolution in action. These body shapes and functions arose and persisted because animals with these survived and thrived when others didn't.

182

FineLetMeSayIt OP t1_j9qbfjw wrote

Thank you for such a wonderfully detailed response! I guess barring an anomaly on your tests, doctors would never think to look for single sided kidney failure. I don't know enough about kidney diseases, but I thought about this because of a coworker/acquaintance who currently has to undergo dialysis. In laymen's logic, it would seem unlikely BOTH of her kidneys failed at the same time. Which means at some point one kidney was doing the job of two, but nobody noticed.

23

lascivious_boasts t1_j9qe4vg wrote

It's actually much more common for both kidneys to fail together.

The underlying causes of kidney failure tend to be systemic (that is affecting the whole body) rather than local.

The big one is diabetes, and barring a blockage in blood supply to one kidney, the main damage is in all the tiny blood vessels that feed each nephron. This usually happens equally between both sides (although occasionally the renal artery stenosis is more of a problem, in which case one side can get a stent to try to maintain its function).

Other big causes are inflammatory/autoimmune. This means anywhere there's a kidney cell/structure the damage occurs. Broadly, this affects both sides at the same time.

55

fiendishrabbit t1_j9tmiei wrote

Though not always. Had a colleague with hereditary PKD and an asymmetric progression (left kidney, non-functional and a huge amount of scar tissue. Enough that they had to remove it when transplanting. Right kidney had been pulling all the weight for the last few years and was now failing as well).

2

puahaha t1_j9qgvnh wrote

Kidney failure is also sinister because you can be asymptomatic even while function is declining until it's really bad, like less than 20~30% functionality. So not only is compensatory action like one kidney fulfilling the role of the other at play, both will have to fail to a very significant degree before you even notice.

17

paceminterris t1_j9t2ctd wrote

While it is true that it is rare to "sense" kidney function decline, it is a trivial matter to detect with blood and urine tests. If you get a blood test every year as part of routine screening, you will catch kidney disease as soon as it begins.

7

wannabe-physiologist t1_j9tkqe3 wrote

Unilateral kidney failure is possible in cases of unilateral nephrolithiasis (kidney stones) however this would be painful enough to prompt someone to go to the ED where the imaging and labs others have mentioned will be done.

In the case of unilateral nephrolithiasis you would expect to see a patient with unilateral flank pain, CVA tenderness, and the urine studies would show red blood cells in the urine. This isn’t technically kidney failure per se, but is one of the ways someone without access to care may develop it.

1

Mediocrasleep t1_j9q65al wrote

Short of imagining, we do not know which kidney is failing. We can see the overall renal health. If it declines, it will prompt some imagining studies (ie. US, CT).

Why no duplicate? Every organ consumes energy. Imagine if your trunk of your body was twice as big… you need to increase caloric intake and it would make you less mobile. The disadvantage > advantage

15

FineLetMeSayIt OP t1_j9qbuaf wrote

But if overall renal health was declining that would mean both kidneys are in jeopardy by then right? The organ energy consumption reasoning makes sense. I wonder why nature chose kidneys as the organ to double up on though. Thanks for the reply!

3

Mediocrasleep t1_j9qckpi wrote

If one kidney suddenly fails, the other kidney usually cannot compensate in time, so labs will show abnormalities. Though even with one healthy kidney, some labs are still abnormal.

But yes, a lot of times, the injuried to the kidneys are happening at the same time (hypotension, drug reactions)

Kidneys are more sensitive to damages and are smaller than other organs as well. On average.

3

fastspinecho t1_j9st4zm wrote

You have two lungs, two liver lobes, two parotid glands, two thyroid lobes, two eyes, two ears, two arms, two thumbs, two legs, two cerebral hemispheres, two gonads, two breasts, etc.

Sometimes the "doubled" organs are so close together that they are considered one (liver, thyroid, brain ...). But that's just developmental happenstance. In some people, the left and right kidneys are combined into one giant "horseshoe" kidney.

2

McHildinger t1_j9rppjj wrote

I was told that the kidneys are somehow related/associated with the ovaries/testis in a fetus, and that is why there are likely two kidneys; people born with only one kidney often only have one functional gonad.

2

Robbo_2991 t1_j9qpbe0 wrote

Here's a new one I found out over the last year. While in the womb, both kidneys can fuse together making a horseshoe kidney. Turns out I've got one. With one tube going to my bladder. It hasn't effected my life so far. But yeah.

But to answer your questions. As others have stated it'll start with blood tests, then if something is found to be abnormal with them it'll progress to an ultrasound then an MRI. That's what happened with me anyway.

7

DoctorStrangeMD t1_j9qmqz2 wrote

Generally doctors avoid invasive procedures (like using an arterial Cather - aka small tube- to inject dye) or using contrast dye in a CT if there is renal dysfunction. Those specific Dye can injure the kidney.

Step 1: blood tests, urine tests. Blood tests for creatinine estimate renal function. If it is abnormally high, this triggers a doctor to investigate more. Urine test, mainly looking for urine protein. If you are losing protein in the urine, the kidney is not functioning right but the creatinine may still be in the normal range. This does not distinguish bilateral or unilateral kidney dysfunction.

Step 2: ultrasound (possibly with Doppler) -ultrasound shows the size of the kidney. This can easily show if 1 kidney is normal and the other is missing or “atrophic.” If a kidney has not been working well for a while; it will start to atrophy. Then you know that kidney is bad. -Doppler with ultrasound can see if the arterial flow is normal and equal. This avoids contrast which can hurt the kidneys.

That’s usually all you need.

But other tests could include MAG3 scan. A nuclear study. This shows how much function is in each kidney. This would definitely show if 1 kidney was failing earlier than another

https://en.m.wikipedia.org/wiki/Radioisotope_renography

Kidney biopsy. Usually though you do not biopsy 2 kidneys. As one reply mentioned it is more common to have kidney damage to both kidneys. Because both kidneys do the same work, they are affected similarly by conditions such as diabetes and high blood pressure that stress the kidney over time.

If 1 kidney was not working well, typically it is congenital, has bad blood flow, or had a blockage that does not allow urine the leave that kidney.

6

medlabunicorn t1_j9qen68 wrote

Couple of things might happen. In the beginning stages, you might put out lots of very dilute urine as your kidneys lose the ability to concentrate urine (other things can cause this , so it’s not definitive). You might put out less and less urine, with objects called ‘casts’ that we can see on the microscope, that are caused by slow flow inside the kidneys (other things can cause this as well, so it’s also not definitive). As it gets worse, your blood chemistries will start to get out of whack, specifically creatinine and electrolytes. If your doctor is looking for kidney failure, one of the things he or she might order is a a blood chemistry panel with an estimated GFR, or glomerular filtration rate; another is a creatinine clearance test, where you collect all of your urine for 24 hours, measure the average creatinine level of your urine over that time, and compare it to the creatinine level in your blood to see if the kidneys are filtering out as much creatinine as they should be.

One kidney, by itself, can do a fine job for you if it’s fully functioning.

5

ThomasEdmund84 t1_j9rzc2q wrote

> EDIT: To piggyback this logic, why don't we have more 'spares' of other organs. Why is the redundancy factor only built into kidneys?

Its likely to do with trade-offs between the resources the human body needs to grow and maintain vital organs and also how feasible having redundancy is.

e.g. lungs are perhaps semi-redundant, obviously having one lung = much reduce physical capacity and isn't great, but we do have two.

My physics might be a little off - but I think its counter productive to have two hearts? Human digestive system already has lots of failures in its complex system so doubling up would probably mean more room for errors.

Two brains? Forget about it.

3

AtrioventricularVenn t1_j9tlu18 wrote

We do have two hearts, one for venous (low pressure) flow and one for arterial (high pressure) flow. Also, each "heart" has its own secondary pump as an additional failsafe mechanism. This is the reason why heart defects or acquired issues can go undiagnosed for several years while the individual still maintains a healthy function.

You can argue that you have at least 3 brains: left and right hemispheres, and the cerebellum. Specialization gives these 3 structures functions and architectures that blur their independence from their counterparts. Damage to any of these structures can be compensated by the others but, of course, the level of compensation varies between individuals and age.

The digestive system is a completely different story because of how embryonic development works. We (and most animals) develop around a whole that becomes our single digestive tube (or tract). We are basically worms with funny looking appendages with wiggly tiny tentacles at their ends.

1

finnky t1_j9qn92y wrote

Evolution doesn’t have an agenda. It’s just random mutation - if it works, great! If it doesn’t, does it harm the individual with it? Yes? It’ll get selected out. No? That mutation will carry on.

Kinda why some organs are in sets and some aren’t.

2

asithaed t1_j9u7pmi wrote

  1. You can check the individual function of each kidney with a DTPA scan.
  2. Yes. Serum creatinine/blood urea like tests will assess the combined function of both kidneys. They will derange only if both kidneys are damaged or one is damaged and the other cannot acutely compensate.
  3. There are many organs in the body with double units or functions in similar way but not anatomically distinguishable as the kidneys. In an advanced medical perspective kidney is the only organ that we can functionally replace 100% with iatrogenic procedures and treatment.
1

Uncynical_Diogenes t1_j9v1zj9 wrote

We have two kidneys not so that one of them can be a spare, but because they evolved from structures that were already pairs. We never gained an “extra” kidney… we still have two kidneys. In most organisms with dedicated kidney-like-organs, you will find these in pairs along the body, probably due to bilateral symmetry during embryogenesis.

Why don’t we have two of other things, for redundancy? Well, unfortunately, the best response to evolution questions is often: ”why would we?” The benefit of evolving an extra of a given organ would have to outweigh the cost. That’s putting energy and time into something that the organism ideally will never need.

Two kidneys for a human-sized organism is pretty cheap, evolutionarily speaking, for your osmotic-filtering-needs. Annelid worms have two nephridia per segment. But two stomachs, two hearts, four lungs? The “cost” rises very quickly for these structures.

That cost is very high when the only time you would need a spare is a life-threatening injury. The only benefit it confers is a higher chance of survival upon taking catastrophic damage. Organisms that sustain life-threatening injuries don’t often survive them - if you’ve taken enough damage to irreparably damage an organ, the chances of you surviving that are not particularly high, even if you have a spare.

1