How do you know a diabetic needs dialysis?

Kidney tests. Usually it takes years of kidney damage from diabetes before you need dialysis. If you're diabetic, you should be getting kidney function and urine tests at minimum yearly, and these will tell us how well your kidneys are working and if you're heading toward dialysis. Your kidneys may be getting worse and without the tests, you might have no idea, so good f/u with your doc is key. Good luck!
Kidney function. The decision to initiate dialysis usually is based on several factors. First laboratory testing can be performed to estimate the glomerular filtration rate. In addition clinical signs are taken into account such as the presence of swelling, poor appetite, weight loss, and decreased level of functioning.