Understanding Kidney Disease: Function Tests, Biomarkers and Imaging

In a standard health check, kidney health is one of the basic items assessed. Kidney health is important because the kidneys help the body eliminate metabolic waste products. Through blood and urine tests that evaluate the kidneys' waste-filtering function and whether the kidneys are excreting excessive protein, it is possible to identify whether the kidneys have been damaged. Below are the items used to assess kidney health during a health check. Not all health check plans include every item listed below, so please read the plan details carefully before purchasing. 

What are the functions of the kidneys? 

The kidneys are part of the urinary system. The two kidneys are located at the back of the abdomen, just below the ribcage (known as the “retroperitoneal” space).  

The main functions of the kidneys include: 

• Filter blood to reabsorb water, glucose (sugar), amino acids, sodium and potassium 
• Excrete metabolic waste products such as urea, uric acid, creatinine, excess water, broken down fragments of medications, hormones and vitamins 
• Producing hormones that help maintain stable blood pressure 
• Over 90% of erythropoietin (a hormone that promotes increased red blood cell (RBC) productions) is produced by the kidneys, and red blood cells transport oxygen throughout the body 
• Producing vitamin D to maintain healthy bones and muscles 

When should kidney function be checked? 

• Blood in urine (haematuria) 
• Difficulty urinating 
• Frequent urination 
• Painful urination 

Types of kidney function tests 

Blood tests 

• Serum creatinine: Creatinine is a substance produced by the normal wear and tear of muscles. Creatinine levels in the blood vary depending on age and body size. If creatinine levels exceed 1.2 in women or 1.4 in men, this may be an early sign of abnormal kidney function. As kidney disease progresses, creatinine levels in the blood will rise.
  
• Glomerular filtration rate (GFR or estimated GFR [eGFR]) : This test evaluates the kidneys' ability to clear waste from the blood. It is calculated (estimated) based on serum creatinine levels, adjusted for age and sex. Normal GFR varies with age (decreasing as age increases). A normal GFR value is 90 or above. A GFR below 60 indicates that the kidneys are not functioning properly. Once GFR drops below 15, treatment for kidney failure, such as dialysis or kidney transplantation, is likely to be required.
• Blood urea nitrogen (BUN) : After eating, protein in food is broken down into urea nitrogen. A normal BUN level is between 7 and 20. As kidney function declines, BUN levels rise. 
  

Imaging tests 

• Ultrasound: An ultrasound scan helps measure kidney size and check whether there are any kidney abnormalities , such as kidney stones or tumours.
• CT scan: A CT scan uses x-rays and computer processing with or without intravenous contrast dye to provide a more detailed examination of whether the kidneys have any stones or structural abnormalities. 
  

Urine tests 

• Urinalysis: This can be divided into microscopic examination of a urine sample and dipstick or urine test strip testing. If abnormalities are detected in the dipstick test, such as excessive protein, blood, pus, bacteria, or sugar in the urine, the  respective indicator blocks will change colour accordingly. Urinalysis helps detect various kidney and urinary tract diseases, including chronic kidney disease, diabetes,  infection, and  stones.
  • Urine protein: Excessive protein in the urine is called proteinuria. A positive dipstick test (1+ or higher) should be confirmed using a more sensitive dipstick test (such as an albumin-specific dipstick) or quantitative measurement (such as the albumin-to-creatinine ratio).
  • Microalbuminuria: People at higher risk of kidney disease, such as those with diabetes or hypertension, should have this test or an albumin-to-creatinine ratio test if their standard proteinuria dipstick test is negative, to confirm their condition.
  • Albumin-to-creatinine ratio (ACR): Albumin is the most common type of protein found in urine. A higher albumin level in the urine may indicate that the kidneys are not functioning properly. It is calculated by dividing the urinary albumin level by the urinary creatinine level.
    • Normal range: An ACR below 30 
    • Moderately increased albuminuria: An ACR between 30 and 300 
    • Severely increased albuminuria: An ACR above 300  

• Creatinine clearance: This test compares creatinine levels in a urine sample with creatinine levels in the blood to show how much waste the kidneys can eliminate per minute. 

Kidney biopsy 

A kidney biopsy involves inserting a fine needle through a small incision into the kidney to extract a small piece of kidney tissue for laboratory analysis. It is an invasive procedure but does not require open surgery. A doctor may request a kidney biopsy in the following situations:

• To make a more accurate assessment of the type and severity of kidney disease the patient has, in order to provide appropriate treatment and determine treatment effectiveness  
• To assess the extent of kidney damage 
• To identify the reasons why a kidney transplant is not performing well 

OT&P Healthcare recommendation 

Kidney health is extremely important to the body's overall health. In addition to urine tests during health checks that can provide insight into kidney health, patients with chronic conditions such as diabetes, high blood pressure, or kidney failure should have targeted kidney function tests performed regularly according to their condition. If you have any questions about kidney health, you can consult our family doctors for an initial assessment or see a specialist for follow-up. 

Read More

• What Should a Full Body Check Up Cover?

References

1. National Kidney Foundation. Tests to Measure Kidney Function, Damage and Detect Abnormalities. Retrieved March 1, 2023, from https://www.kidney.org/atoz/content/kidneytests. 

2. Cleveland Clinic. Kidney Function Tests. Retrieved March 1, 2023, from https://my.clevelandclinic.org/health/diagnostics/21659-kidney-function-tests.

3. 中文大學何善衡泌尿中心. Kidney Function Tests抽取腎組織穿剌檢查程序簡介. Retrieved March 1, 2023, from https://urologycentre.com.hk/zh-hant/diseases/detail/information-on-renal-biopsy.