Using 1/creatinine to assess the possibility of AKI
Many patients with CKD have a slowly progressive decline in function. Often these patients get admitted with a higher creatinine than their previous documented creatinine. We then often quickly label them as having AKI. But we should also consider the possibility that the patient’s new creatinine represents continued deterioration of their CKD.
While not perfect (few if any formulas used for renal disease or fluid and electrolyte disorders are), we can graph 1/creatinine versus time to get a reasonable estimate of expected progression. Here is the idea. For a majority of patients the endless progression to end stage progresses in a straight line of 1/creatinine versus time. One can find this concept used in the trials that showed that ACE-I or ARB slowed the progression of diabetic nephropathy. The investigators calculated the curves slope before and after intervention. A slower slope gave evidence that the drugs delayed the inevitable progression to end stage.
If we have access to records (as we do at the VA system), we can draw a line representing the previous serum creatinines. Extrapolating that line allows us to estimate what the patient’s creatinine would most likely be on admission. A significantly higher creatinine suggests AKI on CKD.
As an example, let’s assume a patient has diabetes mellitus and proteinuria. We have creatinine measurements every 6 months:
Time in months
Creatinine
1/Creatinine
0
1.2
0.83
6
1.3
0.77
...
Source: DB's Medical Rants - Category: Internal Medicine Authors: rcentor Tags: Medical Rants Source Type: blogs
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