What does your kidney/renal function blood test mean - also called U&E or biochem bloods
Most people get a blood test at some time or other, but what do the results actually mean and what are the doctors looking for? Understanding your blood tests properly can help you understand your own health better so you can stay as healthy as possible for as long as possible.
When it comes to your renal function we’re looking at your creatinine, urea, electrolytes and kidney function (eGFR).
Fortunately I’ve made a handy video which explains all about it right here:
To break things down in more detail I’ll tell you what we look for and then what that might mean.
Creatinine
This is a breakdown product from your muscles. Every time you move your muscles, they break down a bit and creatinine is released. Your kidneys are really amazing at filtering pretty much all of it out. However, if your kidneys aren’t functioning so well your creatinine rises.
We use this in an equation to work out your estimated glomerular filtration rate (estimated as we’re not actually measuring your kidney’s glomerulus directly - but extrapolating their function by way of creatinine). As creatinine goes up, eGFR goes down. The lower it gets, the more likely it is to be disease related, rather than just something like dehydration.
When your kidneys go wrong it is either “acute” or “chronic”. Acute = acute kidney injury, and we can treat that in the hospital. Chronic = chronic kidney disease or CKD, and that is a long process over your life staged as follows (and you can read more about it HERE).
Monitoring your eGFR over time is a good way to assess your ongoing kidney function. Things like high blood pressure and diabetes can damage your kidneys.
Urea
Another breakdown product that should be filtered out, so high urea = bad kidneys. You can also have too much protein in your diet which causes urea to rise. We see this more often these days due to all the protein shakes and protein bars that people are eating (unnecessarily!).
Electrolytes
We often put your sodium and potassium in with your kidney function. These ions are the crucial elements to how all the cells in your body work and they are tightly regulated. Potassium should always be within range. If it isn’t it’s a problem and should be explored further. Frustratingly if your blood sample is of poor quality or it was traumatic getting the blood out then your potassium will be high, because broken cells release potassium. You’ll need a repeat test.
Your sodium can go up with dehydration, but if it goes too high it’s a medical issue that needs investigation. Similarly if it drops too low you’ll need your sodium replaced and your doctor will have to figure out why your sodium is so low.