(Notes from BMJ learning module)
Criteria for nephrology referral
- eGFR <30
- A sustained eGFR drop of >25% with change of CKD stage, in a 12 month period
- A sustained eGFR drop of >15 in 12 months.
- An ACR 70 mg/mmol or more, unless related to diabetes mellitus
- An ACR 30 mg/mmol or more with haematuria.
The cutoff between CKD 3a and 3b is eGFR 45. Which is actually easy to remember, since it’s half way and goes with the pattern of dividing into slots of 15. 45 – 59 is 3a, 30 – 44 is 3b.
The full classification then adds A1, 2 or 3 for albuminuria. ACR ❤ is A1 (normal), 3 – 30 is A2 (high), and >30 is A3 (very high).
There is debate about the clinical significance of CKD 3aA1 (no kidding) and it is suggested that patients with this level should have a serum cystatin C test, also known as an eGFRcystatin C – apparently that may come back as 60 or greater even when usual levels are at 3a, in which case the patient doesn’t have CKD 3. eGFRcystatin C can be affected by uncontrolled dysthyroidism.
eGFR can be overestimated in patients with very low muscle mass (frailty or amputation).
Dialysis is normally started (in the UK, at least), at an eGFR of 9.
Acute kidney injury (AKI)
This is diagnosed by either
- an increase in serum creatinine of 26.4 mmol/l or greater
- an increase in serum creatinine of 50% or greater.
eGFRs below 60 should be repeated within 14 days to exclude AKI.
Correction for Afro-Caribbean ethnicity
The factor is 1.159.
More sensitive than PCR at lower levels, but either will work at higher levels. The bit about the first urine of the day is actually not vital unless you suspect orthostatic proteinuria (which causes proteinuria on all except the first sample of the day – it’s more common in the young and usually resolves by the third decade).
There is up to 40% variation between different samples, which is why a raised ACR should always be checked with a second sample.
Patients with hypertension and ACR > 30 mg/mmol, or normotension and ACR >70, should be put on ACE inhib or ARB.
If combined with systemic symptoms, may indicate systemic inflammatory process – check inflammatory markers and if they are raised refer to nephrology even if eGFR normal.
If combined with proteinuria, refer, as above.
The evidence for a renoprotective effect (apart from the antihypertensive effect) exists only in two groups:
- Patients with diabetes plus albuminuria >3 mg/mmol
- Patients with albuminuria >30 mg/mmol
NICE advises offering ACE inhibs/ARBs to patients with the following:
- Diabetes + ACR > 3 mg/mmol
- Hypertension + ACR >30 mg/mmol
- ACR > 70 mmol.
Drops in renal function on taking: If the drop is less than 25% and the rise in creatinine less than 30%, repeat blood test in another 1 – 2 weeks, continuing the same dose of the drug meanwhile. If either the eGFR drop or the creatinine rise is greater than those cutoffs, stop the drug and refer to nephrology to exclude functional renal artery stenosis.
Systolic 120 – 129, diastolic <80
- Diabetes + CKD, or
- ACR >70 mg/mmol
Systolic 120 – 139, diastolic <90
- CKD + hypertension, but no diabetes and ACR <30 mg/mmol.
(So is there a target for non-diabetics with CKD, hypertension, and ACR between 30 and 70? They seem to be falling between those two stools at the moment.)
CHD prevention in CKD patients
NICE recommends all CKD patients should be offered Atorvastatin 20 mg for primary prevention. Aspirin increases the risk of minor bleeds in CKD, but not major; it is recommended where secondary prevention is needed.
May be a harmless finding. Four or more cysts per kidney are required for a PCK diagnosis.