Glomerular filtration rate (GFR)
This is a blood test that measures kidney function – the higher the GFR, the better the kidney function, the better.
A normal GFR number is 90-120 ml/min.
The GFR is used to:
The GFR is also used to place any person in a stage of CKD – the higher the stage (i.e. lower GFR) the worse the kidney function (and disease).
Note 1. CKD1 really means normal (or very nearly normal) kidneys, i.e. little/no evidence of kidney disease
Note 2. CKD1 and CKD2 should be considered risk factors for CKD, rather than a disease
Note 3. Hence being told you ‘have’ CKD1-2 (a ‘disease’) is unnecessarily frightening.
A ‘normal’ uACR level is lower than 3 mg/mmol.
uACR stands for the urinary albumin-creatinine ratio. Albumin is a protein, and this number reflects the amount of protein in the urine. All humans have a little protein in the urine. But if it goes up, it’s is a sign of strain on the kidneys, and sometimes chronic kidney disease (CKD).
So, for this test, a lower number is better. A uACR level of 3-30 mg/mmol is called ‘microalbuminuria’ (= small amount of albumin in the urine). But it can be a sign that you will get higher levels of albuminuria later in the course of CKD.
There are three levels that carry these names:
Note 1. As with CKD1 above, A1 is normal, i.e. no evidence of kidney disease
Note 2. Being told you ‘have’ A1 albuminuria is also unnecessarily frightening.
The urinary ACR levels (‘A1-3′) are combined with the CKD stage (Grade or ‘G 1-5’) to estimate the outlook for someone with CKD – i.e. likelihood of eventually needing dialysis or a kidney transplant – with a higher G and/or higher A, indicating a worse outlook.
In other words, CKD can be described in one patient as ‘CKD G4 A3’, and this has a worse outlook than for a patient with ‘CKD G2 A1’. So a higher level of albuminuria worsens the outlook as does a lower GFR.
But. ACR is often more predictive of outcome than CKD stage.
Hence. A patient with ‘CKD G2 A3’ (GFR 65 ml/min (G2) but heavy albuminuria (A3)) may be at higher risk than someone with ‘CKD G3A A1’ (GFR 45 ml/min (G3A) and no albuminuria (A1)).
We have described what your blood GFR and urine ACR mean, and how they are connected.
As described above, some levels of these classifications are not diseases – in fact they are normal states.
So being labelled as having one (e.g. ‘CKD1-2’ or ‘A1’ ACR) is unnecessarily frightening. Doctors need to explain these issues carefully.
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