Renal function test (RFT) is probably a misnomer: while this group of tests does assess renal function, it is routinely ordered for reasons other than investigating the kidneys. “U+E”, for urea and electrolytes, is probably a more common name for these tests.
Hereunder the author will continue to misrepresent RFTs, but he does acknowledge that the electrolyte studies would have been better discussed elsewhere.
Component tests:
To maintain at least some accuracy, we will deal with the assays for renal function and then the other components of the renal function panel.
Glomerular filtration and other markers of renal function
The best indicator of glomerular function, and thus kidney function, is the glomerular filtration rate. Unfortunately assessment of the GFR is restricted to an academic exercise because we have no suitable endogenous marker to use in routine laboratory testing.
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- Serum creatinine (Female: 45-90μmol/L; Male: 60-110μmol/L)
- eGFR
- Serum urea (2.4-7.5mmol/L) Called, by the Americans, blood urea nitrogen - BUN
The electrolytes in U+E
- Serum potassium (3.6-5.2 mmol/L)
- Serum sodium (135-145 mmol/L)