38. Laboratory diagnosis and monitoring of chronic renal diseases
Chronic kidney disease (CKD), previously called chronic renal failure is defined as the presence of either kidney damage or decreased kidney function for more than 3 months. Decreased kidney function is measured by decreased GFR.
Classification
CKD is classified according to the GFR and the degree of albuminuria:
| GFR category | GFR (mL/min) |
|---|---|
| G1 | > 90 |
| G2 | 60 – 89 |
| G3a | 45 – 59 |
| G3b | 30 – 44 |
| G4 | 15 – 29 |
| G5 | < 15 |
We usually call stage G4 and G5 “chronic kidney failure”, while stage G5 is referred to as end-stage kidney disease (ESKD).
Albuminuria can be categorized either by measuring the total albumin amount in a 24-hour urine sample, or from a single sample where the ratio between albumin and creatinine is measured.
| Albuminuria category | Albumin excretion rate (AER) (mg/24 hours) | Albumin creatinine ratio (ACR) (mg/mmol) | Old term |
|---|---|---|---|
| A1 | < 30 | < 3 | – |
| A2 | 30 – 300 | 3 – 30 | Microalbuminuria |
| A3 | > 300 | > 30 | Macroalbuminuria |
As such, a person with GFR of 43 and AER of 100 is stage G3bA2. A person with a GFR of 100, AER of 5, and polycystic kidney disease has stage G1A1 CKD.
The following laboratory alterations may be present:
- Elevated creatinine and urea, decreased eGFR
- Hyperkalaemia
- Hypocalcaemia with hyperphosphataemia
- Metabolic acidosis
- Dyslipidaemia (especially triglycerides)
- Elevated PTH
- Proteinuria
- Haematuria
Hyperkalaemia can be a problem in CKD, because of the decreased renal elimination of potassium and because of the RAAS inhibitors’ tendency to cause it. Treatment may be necessary.