A man with severe leg painBMJ 2019; 365 doi: https://doi.org/10.1136/bmj.l1301 (Published 22 May 2019) Cite this as: BMJ 2019;365:l1301
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A case of a man with acute lower limb compartment syndrome was published in the Journal : BMJ 2019;365:l1301
A table of relevant investigations was included. The patients creatinine was above the upper limit of normal (45-89umol/l). This was described as constituting acute kidney injury (AKI). To constitute an acute kidney injury a greater than 26umol/l rise above base line is required. For this to be stated within accepted definition, a recorded base line result for the patient would be needed. The baseline may not have been known and wasn’t stated.
The table included the patients estimated glomerular filtration rate (eGFR). The use of eGFR was derived for use in chronic kidney disease and should be limited to areas where it has been validated. Its use in acute illness is discouraged by UK Renal association and other national bodies, as eGFR is not validated in this context.
The ‘e’ in e as the eGFR stands for estimated (stated in full in the table). This estimation is based a number of assumptions, including a stable serum creatinine, and excluding situations when the serum creatinine is changing rapidly, as in acute kidney injury. As this patient was acutely unwell the eGFR should not be regarded as an appropriate or relevant result.
The relationship of creatinine to GFR is complex, variable and prone to mis-interpretation. The eGFR is based on the serum creatinine and has further limitations. The use of the eGFR in unintended cirucumstances can lead to error and as in this case should not be used in the acute context.
Some hospitals have chosen not to include eGFR report as an item in patients attending hospital in order to avoid this confusion. Unfortunately this has not been a uniform practice and routine use of eGFR has can be found being reported in many hospitals automatically in patients where it is not appropriate.
For example, the laboratory can provide the calculated or eGFR on any measured creatinine even when the patient has a true GFR of zero, and is functionally or practically anephric.
The discussion of the case emphasizes potential AKI, importance of fluid resuscitation and electrolyte balance. The case is also linked to CPD and learning modules.
Given the creep of eGFR reporting in hospital (as demonstrated by its inclusion in the table of relevant investigations), some discussion of the use and deficiencies of this metric would enhance the learning from this case.
When using a test, it’s important to know your limitations.
Competing interests: No competing interests