How frequently during myeloma treatment is a urine creatinine clearance test done? Can there be renal dysfunction when the serum creatinine is normal, BUN is normal, and the creatinine level in the 24-hour urine test also is normal?
I ask this question because I recently asked my oncologist to order a creatinine clearance test. She did so, but very reluctantly. In her practice, it is never done, she told me. When the results came back, the lab had failed to do the creatinine clearance test, but did report the actual level of my urine creatinine as normal. I did not pursue the matter because I assumed that if I had some renal dysfunction, my urine creatinine level would be abnormal. However, perhaps I should not assume.
I asked for the creatinine clearance test because months ago, when one was done in my preparation for a scheduled stem cell transplant, the result came back as abnormal, although all other relevant markers were normal. This was surprising, but evidently not disturbing, to my doctors. (My creatinine level has always been at 0.7 or 0.8 and BUN as well as BUN / creatinine ratio have always been normal.)
I welcome a response from anyone who is knowledgeable about this issue.
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Re: Frequency of creatinine clearance test?
I have a BLOOD chemistry workup every time I see my oncologist, which includes the blood creatinine and creatinine clearance. I have only had a 24-hour urine test a couple of times in the 3 years since I was diagnosed.
Cathy
Cathy
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antelope1225 - Name: Cathy1225
- Who do you know with myeloma?: Myself
- When were you/they diagnosed?: May 25 2012
- Age at diagnosis: 55
Re: Frequency of creatinine clearance test?
Cathy, I must not understand what creatinine clearance means. I thought it was a comparison of the SERUM creatine level to the URINE creatinine level, taking urine volume over 24 hours into account. Am I mistaken?
Re: Frequency of creatinine clearance test?
Hi Mrozdav,
You're correct that actual measurement of the creatinine clearance is based on the calculation you described. However, you also can estimate someone's creatinine clearance based on their serum creatinine level, weight, and age, among other variables. The Wikipedia article on renal function has a good discussion of both the calculation you described and the serum creatinine-based estimate of creatinine clearance:
https://en.wikipedia.org/wiki/Renal_function#Estimated_values
It's the estimated creatinine clearance that is probably in Cathy's test results. If your own blood test results don't have such estimates, there are online calculators that will churn out creatinine clearance estimates using your serum creatinine level and other inputs you'll have to provide (age, gender, etc).
Note that it's really the glomerular filtration rate that you want to measure to assess kidney health, but it's not an easy thing to measure, so it is usually estimated using formulas that also have the serum creatinine level as one of the inputs (see the Wikipedia article for some examples). The "eGFR" (estimated glomerular filtration rate) also is often reported in blood test results, but it is once again just an estimate based heavily on the serum creatinine level.
I hope this helps at least a bit, and sorry if I'm just telling you things you already know.
You're correct that actual measurement of the creatinine clearance is based on the calculation you described. However, you also can estimate someone's creatinine clearance based on their serum creatinine level, weight, and age, among other variables. The Wikipedia article on renal function has a good discussion of both the calculation you described and the serum creatinine-based estimate of creatinine clearance:
https://en.wikipedia.org/wiki/Renal_function#Estimated_values
It's the estimated creatinine clearance that is probably in Cathy's test results. If your own blood test results don't have such estimates, there are online calculators that will churn out creatinine clearance estimates using your serum creatinine level and other inputs you'll have to provide (age, gender, etc).
Note that it's really the glomerular filtration rate that you want to measure to assess kidney health, but it's not an easy thing to measure, so it is usually estimated using formulas that also have the serum creatinine level as one of the inputs (see the Wikipedia article for some examples). The "eGFR" (estimated glomerular filtration rate) also is often reported in blood test results, but it is once again just an estimate based heavily on the serum creatinine level.
I hope this helps at least a bit, and sorry if I'm just telling you things you already know.
Re: Frequency of creatinine clearance test?
TerryH and Cathy, Thank you for your respective inputs. I am still a little puzzled, however.
Cathy, I, too, get monthly blood tests done. These check for my creatinine and eGFR , which I assume, perhaps wrongly, is what you think is creatinine clearance. My eGFR calculation (always normal, so far) is based on the MDRD equation, but the lab report states that if a patient is 70 years or older, the Cockroft- Gault equation should be used. I am 70.5 years old. It would appear that in my case the lab is not using the correct formula although staff is certainly aware of my age. In the same vein, the lab does not know my weight or height, so I do not know how they can estimate my glomerular filtration rate.
The article TerryH cited sets forth that " an unexpectedly low or high 24 hour creatinine excretion rate voids the test." That would appear to allay some of my concerns caused by my March creatinine clearance test results. The same article, however, states: " blood BUN and creatinine will not be raised above the normal range until 60% of total kidney function is lost."
My doctors seem to be relying on the monthly serum creatinine, BUN, and eGFR results to conclude that all is well with my kidneys. I suppose I am wondering whether, after a year of myeloma treatment, a visit to a nephrologist to check out my kidney function is warranted.
Cathy, I, too, get monthly blood tests done. These check for my creatinine and eGFR , which I assume, perhaps wrongly, is what you think is creatinine clearance. My eGFR calculation (always normal, so far) is based on the MDRD equation, but the lab report states that if a patient is 70 years or older, the Cockroft- Gault equation should be used. I am 70.5 years old. It would appear that in my case the lab is not using the correct formula although staff is certainly aware of my age. In the same vein, the lab does not know my weight or height, so I do not know how they can estimate my glomerular filtration rate.
The article TerryH cited sets forth that " an unexpectedly low or high 24 hour creatinine excretion rate voids the test." That would appear to allay some of my concerns caused by my March creatinine clearance test results. The same article, however, states: " blood BUN and creatinine will not be raised above the normal range until 60% of total kidney function is lost."
My doctors seem to be relying on the monthly serum creatinine, BUN, and eGFR results to conclude that all is well with my kidneys. I suppose I am wondering whether, after a year of myeloma treatment, a visit to a nephrologist to check out my kidney function is warranted.
Re: Frequency of creatinine clearance test?
Hi TerryH and mrozdav.
I learned something new! I didn't realize that the creatinine clearance is a comparison of serum creatinine level to the level in urine.
My blood test does describe it as the estimated creatinine clearance. I have heard that the estimated creatinine clearance is an estimate of the percent of your kidney that is functioning. So 33 is an estimate that 33 percent of your kidneys are functioning properly.
Right, Terry?
Cathy
I learned something new! I didn't realize that the creatinine clearance is a comparison of serum creatinine level to the level in urine.
My blood test does describe it as the estimated creatinine clearance. I have heard that the estimated creatinine clearance is an estimate of the percent of your kidney that is functioning. So 33 is an estimate that 33 percent of your kidneys are functioning properly.
Right, Terry?
Cathy
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antelope1225 - Name: Cathy1225
- Who do you know with myeloma?: Myself
- When were you/they diagnosed?: May 25 2012
- Age at diagnosis: 55
6 posts
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