Kidney Function Tests (Creatinine, Urea)
The kidneys filter waste products from the blood and remove them in the urine. Kidney function tests measure some of these waste products, mainly creatinine and urea, to show how well the kidneys are working. They can detect kidney problems long before any symptoms appear.
At YGOPH, these tests are requested for pregnant women with high blood pressure or pre-eclampsia, before CT scans with contrast, for children who are severely dehydrated or have kidney disease, and for patients taking medicines that can affect the kidneys. Our paediatric nephrology clinic uses them to follow children with conditions such as nephrotic syndrome.
What do kidney function tests measure?
Creatinine is produced by the muscles at a fairly steady rate and removed by the kidneys; when the kidneys filter less, its level rises. Doctors use it to estimate the glomerular filtration rate (eGFR), a measure of the kidneys' filtering capacity. Urea comes from the breakdown of proteins and rises with kidney problems, dehydration or bleeding in the gut. Uric acid is often added in pregnancy, as it may rise in pre-eclampsia.
- High blood pressure or pre-eclampsia in pregnancy
- Severe diarrhoea, vomiting or dehydration, especially in children
- Swelling of the face or legs, or protein in the urine
- Before a CT scan with contrast or certain medicines
- Monitoring of diabetes, sickle cell disease or HIV treatment
Good to know
Creatinine and eGFR
Normal creatinine depends on muscle mass, so it is lower in children and women than in men, and it naturally falls during pregnancy because the kidneys filter more. A value that looks normal for another adult may therefore be abnormal in a pregnant woman, which is why results are always interpreted by a doctor.
Urea and uric acid
A high urea with a normal creatinine often points to dehydration. Uric acid is useful in the follow-up of pre-eclampsia and gout. Your doctor may also request electrolytes and a urine test for protein to complete the assessment of your kidneys.
Children's kidneys
Kidney problems in children include urinary tract infections, congenital malformations, nephrotic syndrome and complications of severe malaria or dehydration. Reference values for creatinine vary with age and height, and the paediatric team estimates kidney function using formulas designed for children.