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Reciprocal creatinine plots (AKA 1/creatinine vs time) - why internists should understand this concept.
#5goodminutes #KashlakChief @thecurbsiders I hope @kidney_boy will comment and correct any errors
First, this is not a perfect concept, but it is useful for 3 reason. The concept follows from the observation that for most patients, GFR decreases linearly.
Since the creatinine clearance formula has creatinine in the denominator, we can use 1/creatinine as a substitute for estimated GFR. Thus these plots show us the usually relentless progression to ESRD in most patients with significant CKD.
The first reason to understand these plots is to predict the progression to ESRD, so that we can prepare the patient for dialysis or transplantation. Once one has sufficient data, one can extrapolate the line so that one can estimate the time for the need for ESRD treatment.
This website offers a pdf download to make your own plots for patients. edren.org/pages/handbook…
Second, when patients have a "newly elevated" creatinine we can use these plots to determine whether the new creatinine is the normal progression of their CKD or an acute elevation. This explains why I dislike the term "baseline" creatinine. I prefer most recent creatinine.
CKD patients often have creatinine levels that "fall below the line" of progression. This knowledge should invoke an important differential dx. My quick list - obstruction, volume contraction, toxins (especially meds, especially NSAIDs), any normal cause of ATN, infection.
We see two common examples of this use. Some patients get admitted after greater than one year from their last "touch" with the system. Their most recent creatinine was 2.2, and now their creatinine is 2.8.
In such patients, we should not assume an acute event w/o considering the previous progression of their CKD. Of course, we should always ask if the patient could have an acute insult, but if nothing is obvious, we can more easily slow down investigation if the graph fits.
Finally, as we read the literature on CKD, many studies use the slope of this plot as an indicator of delaying progression of CKD. If you read the ACE-I or ARB studies with diabetic CKD you will see this measure.
You will often see a plot if 1/creatinine vs time that shows a flattening of the line starting with the intervention group compared to the steady downward graph of the placebo group.
I hope this brief introduction to these plots may help you understand the literature, the expected progression of CKD and better understand when the patient needs preparation for ESRD management.
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