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Creatinine level repost
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diitto posted:
Hi... I have Renal Artery Stenosis of the right kidney, discovered in 2003. That kidney has shrunk away and the nephrologist decided long ago to let it go (not enough function remaining to make it worth trying to open the artery... Before fading away that right kidney drove my blood pressure to toxic levels (220/135) which did some damage to the left kidney and we have been carefully monitoring function since...

A couple of years ago, the blood chemistry lab my doctor uses changed the limits for serum creatinine from old limits of 0.8 - 1.3 mg/dL to new limits of 0.61 - 1.24 mg/dL? (mean shifted down from 1.05 to 0.93 and entire range made a little bit larger, old range of 0.5 increased to 0.63)


When the old limits were in place, my creatinine ran between 1.3 and 1.6? When the new limits went into effect, for reasons unknown, my creatinine readings suddenly fell right into the middle of the new spec? So far so good I guess? I have now had four tests (about once every 6 months) against the new limits and those results have been (in chronological order)


0.96 mg/dL
0.91 mg/dL
1.08 mg/dL
1.16 mg/dL


Yesterday I got the 1.16 results and I asked the nephrologist if she was concerned about the last three readings having gone from 0.91 (great) to 18% higher for the 1.08 and then another 7% higher for today's 1.16 reading? After all, higher is not good?


She said she was NOT concerned, that changes of +/- 10% aren't really real (just within measurement error)... But she doesn't really stare at the numbers like I do... (She obviously sees these numbers a lot and makes quick judgements about what matters and what is within normal error bars). But note that the change a couple of tests ago from .91 to 1.08 certainly WAS greater than 10% (it was an 18% change)...


Anyway, does anyone have any thoughts about serum creatinine level changes like I am reporting here???? Any feedback would be much appreciated...


thanks.. bob...
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John-SKPT responded:
I think that the neph ia right about the 10% acceptable lab variance. That's been a rule of thumb for a long time; tests just are not perfect snapshots when you are watching a long-term trend.

On top of the lab variance, you have to account for the body's own variability: hydration, exercise, time of day, etc.

Personally I always found the second decimal place a little silly. The lab that I've been getting numbers from over the last 10 years reports the numbers that way, but for practical purposes the docs at that hospital just ignore the second digit (1.10 and 1.15 are both counted as 1.1).

The four numbers that you cite are, for all practical concerns, the same. 1.1 to 1.4 is worth looking at, but 1.0 to 1.1 or 1.2 probably is insignificant.


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