When should I see a kidney specialist?

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A question from one of our email subscribers: Dear Dr. Michael Aaronson, I have a friend with childhood onset sugar diabetes. She is 40 years old. She takes great care of herself. She recently got an insulin pump and her sugars have been great. She exercises everyday. After seeing her primary care provider, she was told her GFR (her level of kidney function) was down to 50 (normal is 100) --this was 2 weeks ago. 6 months prior it was 56. They said they'd recheck it in 3 months.

Well, this week she got short of breath and was concerned that she was having a heart attack. She had a stress test today that went well. They rechecked her GFR though and it was 43. Her primary doctor told her if it goes below 40 she's going to have her see a nephrologist / kidney specialist. A kidney U/S showed that her kidneys were slightly smaller than normal but had good blood flow. They are rechecking her kidney function in 1 week.

Any thoughts? I wonder if the worsened kidney function is a fluke or something we should be concerned about? Thanks!

Dr. Michael L. Aaronson, MD, Renal Specialist: Thank you for asking this question. Understanding kidney function can be complex. Let me simplify. Even though we normally have about 2 million kidney filters, kidney doctors say that a person with no kidney problems has 100 filters. These 100 filters perform the job of removing toxins and fluid from the body every day. In doctor-speak, this person has a "GFR" or filter rate of 100 per cent function.

Over time, people with diabetes and high blood pressure can damage some of the filters. The woman in our case study has 50 out of 100 filters to do the job (50 per cent function). These filters have a lot of work to do, but they can get it done and a person doesn't have to get kidney dialysis.

As more and more filters get damaged, the remaining ones start to get overworked. Eventually when there are 10 to 15 filters left, the filters are unable to remove the toxins and fluid from the body, and the patient requires an external filter (a kidney dialysis filter) to get the job done.

Primary care physicians have different cutoffs in terms of the GFR the patient has to have before they are willing to consult a kidney specialist. Of course I am happy to see a patient at any level of kidney dysfunction and for any reason. However, I would much rather have 60 filters to work with than 40.

When there are only 20 to 30 filters left, my job gets harder and the chances of preventing kidney dialysis are even worse. Many nephrologists or kidney doctors would recommend consultation when the kidney function, the GFR drops below 60. This is the magic number.

A lot of things change in the body when the GFR is around 60 or below. People can become anemic, tired and fatigued. People can have major bone problems. People can have potassium and other electrolyte problems. Kidney specialists can help the primary care physician with these kidney specific issues. What's more, targets for blood pressure and cholesterol are lowered. So control becomes harder to obtain. Kidney consultants can help the primary care doctor and the patient achieve these new goal targets.

In this case, I do agree with checking a blood test in one week. However, whether or not the lower number was a fluke doesn't change the fact that this woman needs to see a kidney doctor. In addition to what was just mentioned, I would like to know if the patient has any protein or blood in her urine. If she has protein, she would be a candidate for a medications such as benazepril to help prolong the life of her kidneys -- even if her blood pressure is normal! Iron studies to evaluate for iron deficiency anemia would also be indicated. Target blood pressure should be 130/80, and I would argue that the patient should have an LDL (bad) cholesterol of 70 or below, triglyceride level of 150 or below,and HDL (good cholesterol) of 40 or above. If there is any evidence of secondary hyperparathyroidism, the person needs to be treated.

Make sure your physician tells you what your GFR is. Terms like "creatinine" have less meaning and is not enough information, because your creatinine level is only a rough estimate of your true kidney function.

Now you know if the number is below 60 you should see me. If the number is trending down quickly, even if it is above 60, you should see me. If you are concerned, you should see me. My goal at that time would be to prevent further worsening of kidney function so that you never see the kidney dialysis machine. However, it is important to note that if you do need kidney dialysis, I can help you with that.