What does my blood GFR and urine ACR mean?

What does my blood GFR and urinr ACR mean – and how are they connected?

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 eGFR number is 90-120 ml/min.

What is GFR used for?

The GFR is used to:

• Diagnose CKD
• Monitor – changes in kidney function over time
• Decide – whether you need dialysis or a kidney transplant.

GFR and CKD Stage

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.

Urinary ACR

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 mg/mmol or higher is called ‘microalbuminuria’ (small amounts of albumin in the urine). It can be a sign that you will get higher levels of albuminuria later in the course of CKD.

Categories (levels) of albuminuria/uACR

There are three levels that carry these names:

• A1 = <3 mg/mmol. Normal, as it is normal to have a very small amount of albumin (and protein) in the urine
• A2 = 3-30. Mild albuminuria
• A3 = >30. Moderate-to-severe albuminuria.

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.

5 CKD stages: and how GFR and ACR are connected

These 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’ (red zone below), and this has a worse outlook than for a patient with ‘CKD G2 A1’ (yellow zone below). So a higher level of albuminuria worsens the outlook as does a lower GFR.

This table shows how urinary ACR and GFR affect the outlook for CKD. The green areas above really mean no significant kidney disease.

Summary

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.