So here goes:
I go get blood tests of creatinine and cystatin. Then I get the results. They tell me that my eGFR is barely passing. A little lower and I am classified as having CKD.
Here are the results:
Because of this condition, my blood volume is much lower than normal. Given that my blood volume is lower, the colloids/substances in my blood would be more concentrated. This is why my RBC, hemoglobin, and hematocrit is on the high side. And this also why my serum LDH is higher than range (even if my hsCRP and ESR values are normal). It reasons that my creatinine and cystatin c values would also be more concentrated, and thus readings would be higher.
The eGFR calculations based on creatinine, or on creatinine and cystatin c, are based on the assunption of normal blood volume only (as I would assume here, not sure though). Applied to my situation, the estimates would make my estimated GFR appear lower than what it really is.
To back up my statement, I went back to a 24hr urine collection I had done a year and a half ago (Okay, not very recent, but I can take another one when I get a chance). Based on this, I was able to calculate a creatinine clearance of 105 ml/min (I don't know why it doesn't include ml/min/1.73m2 though).
Given that kidney produces its own creatinine and this would bump the creatinine clearance by about 20%, I would divide this value by 1.2, such that 105/1.2 = 87.5 ml/min
Compared to the eGFR from creatinine and cystatin c, which is 61, there is a large discrepancy.
Now, let's assume that normal blood volume is 5 liters, and my blood volume is only 4 liters. If I normalize the my serum creatinine and cystatin c values:
creatinine would go down from 115.70 to 115.7 (4/5) = 92.6, and
cystatin c would go down from 1.19 to 1.19 (4/5) = .95
If I used these values and plugged them in into the calculator at GFR Calculator, my eGFR would be 82 ml/min/1.73m2.
This would align more closely would my creatinine clearance value of 87.5 ml/min.
Please let me know if I'm making sense here. Aren't these eGFR estimates hokey when the people who use it don't properly account for factors that would invalidate eGFR values? And hence, aren't they liable to cry wolf by telling people they're worse off than they really are? And wouldn't people be treated for nonexistent conditions?
@Dan Wich @Blossom @tara @ecstatichamster @DaveFoster @Rafael Lao Wai what do you think?
p.s. Maybe the eGFR is correct, but shouldn't my blood volume naturally lead to a lower GFR just the same, and maybe there is really no cause for alarm for my lower GFR? After all, the total amount of creatinine in my system isn't really higher, right? And my kidneys are still excreting creatinine at a healthy rate, as evidenced by the 24hr urine collection.
I go get blood tests of creatinine and cystatin. Then I get the results. They tell me that my eGFR is barely passing. A little lower and I am classified as having CKD.
Here are the results:
- Serum creatinine only
- creatinine- 106 umol/L (range 59- 104)
- eGFR- 62.76 ml/min/1.73m2 (range 85-125)
- Serum creatine and cystatin C
- creatinine- 115.70 umol/L (range 64-104)
- cystatin c- 1.19 mg/L (range 0.41 - 0.99)
- eGFR - 61 ml/min/1.73m2
Because of this condition, my blood volume is much lower than normal. Given that my blood volume is lower, the colloids/substances in my blood would be more concentrated. This is why my RBC, hemoglobin, and hematocrit is on the high side. And this also why my serum LDH is higher than range (even if my hsCRP and ESR values are normal). It reasons that my creatinine and cystatin c values would also be more concentrated, and thus readings would be higher.
The eGFR calculations based on creatinine, or on creatinine and cystatin c, are based on the assunption of normal blood volume only (as I would assume here, not sure though). Applied to my situation, the estimates would make my estimated GFR appear lower than what it really is.
To back up my statement, I went back to a 24hr urine collection I had done a year and a half ago (Okay, not very recent, but I can take another one when I get a chance). Based on this, I was able to calculate a creatinine clearance of 105 ml/min (I don't know why it doesn't include ml/min/1.73m2 though).
Given that kidney produces its own creatinine and this would bump the creatinine clearance by about 20%, I would divide this value by 1.2, such that 105/1.2 = 87.5 ml/min
Compared to the eGFR from creatinine and cystatin c, which is 61, there is a large discrepancy.
Now, let's assume that normal blood volume is 5 liters, and my blood volume is only 4 liters. If I normalize the my serum creatinine and cystatin c values:
creatinine would go down from 115.70 to 115.7 (4/5) = 92.6, and
cystatin c would go down from 1.19 to 1.19 (4/5) = .95
If I used these values and plugged them in into the calculator at GFR Calculator, my eGFR would be 82 ml/min/1.73m2.
This would align more closely would my creatinine clearance value of 87.5 ml/min.
Please let me know if I'm making sense here. Aren't these eGFR estimates hokey when the people who use it don't properly account for factors that would invalidate eGFR values? And hence, aren't they liable to cry wolf by telling people they're worse off than they really are? And wouldn't people be treated for nonexistent conditions?
@Dan Wich @Blossom @tara @ecstatichamster @DaveFoster @Rafael Lao Wai what do you think?
p.s. Maybe the eGFR is correct, but shouldn't my blood volume naturally lead to a lower GFR just the same, and maybe there is really no cause for alarm for my lower GFR? After all, the total amount of creatinine in my system isn't really higher, right? And my kidneys are still excreting creatinine at a healthy rate, as evidenced by the 24hr urine collection.
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