Sounds pretty serious. You should get a good physical. Are you sure it is your kidneys? Do you have FATIGUE? Ask the doctor whether or not you have any blood in urine
I spoke with a man a couple of days ago who was the son of a Vietnam Vet. So prior to his conception, the propellant with Dioxin or AO could have a 'head start' on health damage for him, too. I suspect a chemical with BUTYL or 2-butoxyethanol
This man also was in the industrial painting profession. And he was starting to notice that his kidneys hurt every time he was painting. He used good protective equipment, but now refuses to take off his face mask on the work site when urged to by his co-workers ... to 'chat'
On top of that he had been staying in the company 'bunk house' and that would cause more exposure to a harmful chemical component in paint - second hand exposure: as co-workers nearby are breathing out the chemical in their respiration, it can get into the eyes of those who are sleeping in the same room. A health hazard for fire dept personnel, etc
The chemical I looked into is said to cause autoimmune hemolytic anemia and it also appears to cause the odd assortment of symptoms of Chronic Fatigue Syndrome (CFIDS, FM, etc). Autoimmune issues in general and it targets the liver and kidneys, blood & blood forming organs, lymph system, nervous system, defats the skin, etc
The kidneys help make red blood cells (send a hormone to the bone marrow) and help make strong bones.
You didn't say what kind of work you did.
What kind of work does your mate do? ....if you are married
Do you do anything (like cleaning) that causes farting, diarrhea, 'the sniffles?' flu symptoms?
When you say kidneys, are you referring to your back or flank? Are there other signs or symptoms present? Pain caused by the kidneys is typically felt in the flank area. Pain caused by the kidneys tends to be sharp, severe and occur in waves. As opposed to dull aching pain, which is usually due to muscles, ligaments, or even vertebrae and disks in the spinal column. Musculoskeletal pain typically gets worse with movement, and is relieved by heat or massage.
Common causes of kidney pain include kidney stones, kidney infection or pyelonephritis, and any bleeding within the kidney from injury or otherwise, where the blood supply is suddenly cut off because of blockage of the artery to the kidney.
It would be best to have it evaluated by your doctor. Ultrasound or xray may be done to better visualize the structures. Take care and keep us posted.