Curious...SD point

[tantemorte]

I'm really curious....what is the standard deviation point in GFR?
Definition AND number.
I think I get the definition but I can't seem to find the actual number.

[Clark]

Interesting question. It's known to vary from lab to lab and test to test in the same individual, but I don't know if that variance is characterizable as other than error. The are also constants in the estimate techniques from historical curve fitting exercises with unquantified applicability to an individual now. Or are you asking about the mean and standard deviation for the entire human population? "Normal" in the literature is 100-130 ml/min/1.73m2 for up to age 40, but this is not a normal distribution around a mean, it's a functional definition. Higher is unaddressed in the literature, and may be meaningless as a statistical distribution as it is not sampled in any rigorous way. Lower is studied as potential renal insufficiency, typically diagnosed due to presentation of symptoms of complications. In almost all disease presentation, including normal aging, deterioration occurs at some progressive rate. Injury, or amputation, as we experience, is a sudden change.

There are many variables in judging GFR. A lot are addressed in
KDOQI Clinical Practice Guidelines for Chronic Kidney Disease: Evaluation, Classification, and Stratification
PART 4.  DEFINITION AND CLASSIFICATION OF STAGES OF CHRONIC KIDNEY DISEASE
GUIDELINE 1. DEFINITION AND STAGES OF CHRONIC KIDNEY DISEASE
http://www.kidney.org/professionals/kdoqi/guidelines_ckd/p4_class_g1.htm

[tantemorte]

No,I'm asking specifically about the standard deviation point...as in 2 standard deviation points below the GFR for an age group.
What is & how much is a standard deviation point?

[Clark]

So, that would rely on adequately sampling the population of interest to parameterize the distribution. The report I linked to has some of that detail, but I don't know of any studies that have the rigor needed to get you what you're seeking. As I said, the threshold values are functionally based, not statistically defined, so I don't know if anyone's ever gone looking for the nature of the distribution. Most people are never tested, those who are tested are generally tested only as a diagnostic tool indicated by adverse symptoms, if the testing technology and medical expertise are even available. This is a biased sample, and not even all of these results have been well recorded or sampled worldwide throughout history to reveal trends in symptom presentation, medical testing practice, technology diffusion, or actual end stage renal disease prevalence. That would be interesting, and useful in policy and medical practice standard development, even if it didn't reveal the normal distribution of GFR in the unsampled, healthy or untreated majority of the population.

[tantemorte]

"Most programs now use 80 mL/min/1.73 m2 as their cutoff, although 25% of programs now require the creatinine clearance be within two standard deviations of the mean creatinine clearance for the donor's age"

What does this mean? I need an actual example,as in,if creatinine is X then standard deviation is Y.

It says standard...that usually means something already set in some way or another,especially if it's being used to determine donor eligibility. I've found this phrase used in several publications now & I really want to understand it but googling it is no help.
Perhaps one of the doctors on here could explain it.

[tantemorte]

http://www.kidney.org/professionals/kdoqi/guidelines_ckd/Gif_File/kck_t25.gif

I mean,this is the only thing I can find.

So according to this, in the age range of 30-39 females the mean GFR is 107,the standard deviation is 21 so does that make a potential donor eligible in that age group with a GFR as low as 65??

[Clark]

Again, it's about functionality, not just where one falls in the distribution of values in the population. This makes it unlikely, to the point of irresponsibility, that any transplant center would approve a donor candidate to proceed with a GFR < 90.

[tantemorte]

Actually, a lot of center use the international cut off point of 80GFR,including mine (& mine took me with a GFR of 78-80 as a 32 yr old--not that I would've agreed to it,had they told me it was that low instead of telling me it's 100)....& I've heard of a number of donors who were even under 80,especially older (50s-60s) ones. You can see why it's such a point of curiosity to me.