Kidney function tests
Also known as: urea and electrolytes, renal function tests, renal profile
Creatinine and urea are waste products the kidneys should clear; how much builds up in blood shows how well they are filtering. Creatinine is converted into an estimated filtration rate (eGFR), the standard measure of kidney function.
- Abbreviations
- U&Es, U&E, RFT
- Kind
- Test panel
- Categories
- Kidney & urinary, Chemistry & metabolic
- Specimen
- Serum
- Method
- Chemistry analyser, Calculation from other results
- Component tests
- Creatinine and eGFR, Creatinine and eGFR
- Terminology
- LOINC 24362-6
- Type
- Blood test
- Sample
- Blood from a vein
- Used for
- Kidney function, dehydration, electrolyte balance, drug monitoring
- Measures
- Urea, creatinine, eGFR, sodium and potassium
- Result
- A panel of numeric values with laboratory reference intervals, plus an eGFR read against staging thresholds
Why is it used?
- Screening people with diabetes or high blood pressure
- Before contrast scans and many drugs
- Swelling, reduced urine, tiredness, nausea
- Dehydration, vomiting, diarrhoea
- Monitoring ACE inhibitors, diuretics, lithium and NSAIDs
What does it measure?
| Component | What it measures | A higher value may be seen in | A lower value may be seen in |
|---|---|---|---|
| Creatinine Cr | Muscle waste product cleared by the kidney | Reduced filtration, dehydration, high muscle mass | Low muscle mass, pregnancy |
| eGFR (estimated glomerular filtration rate) eGFR eGFR | Estimated filtration rate | Normal in the young | Chronic kidney disease, acute kidney injury |
| Urea urea | Protein waste made by the liver, cleared by the kidney | Kidney impairment, dehydration, gut bleeding, high-protein diet, steroids | Liver disease, malnutrition, pregnancy |
| Sodium Na | Main extracellular ion; reflects water balance | Water loss without replacement | Excess water, SIADH, thiazides, heart or liver failure |
| Potassium K | Main intracellular ion; sets cardiac excitability | Kidney impairment, ACE inhibitors, ARBs, spironolactone, haemolysed sample | Vomiting, diarrhoea, diuretics, steroids, salbutamol |
A high or low value can be associated with several different situations; the result is interpreted with other results, symptoms, history and clinical findings.
How is it performed?
Venous blood; usually paired with a urine protein test.
Specimen. Venous blood (serum); usually paired with a urine sample
Do I need to prepare?
None; avoid heavy exercise or a large meat meal the day before if possible.
What do the results generally mean?
| Finding | What it may indicate |
|---|---|
| Rising creatinine over hours to days | Acute kidney injury: dehydration, sepsis, obstruction, drugs; usually reversible if caught |
| eGFR below 60 on repeated tests | Chronic kidney disease, staged 3-5 by the value |
| High urea, normal creatinine | Dehydration or gut bleeding rather than kidney damage |
What can affect the result?
- Hydration, recent vomiting or diarrhoea and intravenous fluids
- Muscle mass, diet (meat), creatine supplements and exercise
- Sample handling: a squeezed, delayed or haemolysed sample raises potassium
- Medicines: ACE inhibitors, ARBs, diuretics, NSAIDs, trimethoprim, lithium
Medicines. ACE inhibitors, ARBs and potassium-sparing diuretics raise potassium and creatinine; loop and thiazide diuretics lower potassium and sodium; NSAIDs, lithium and contrast can reduce filtration; trimethoprim raises creatinine without harming the kidney.
What can the test not tell you?
- The cause of kidney impairment or whether it is reversible
- Protein or blood in the urine, which need urine tests
- Total body potassium or sodium, only their blood concentration
eGFR is an estimate; it is inaccurate at extremes of muscle mass, in pregnancy and in rapidly changing illness. Half of kidney function can be lost before creatinine leaves the normal range.
Other tests commonly used with it
Medicines monitored with this test
Each medicine page cites the official document that names this test in its monitoring plan.