Liver Function and Kidney Function Tests

What are the Liver and Kidneys?

Both the liver and kidneys are vital body organs, essential for survival.

The liver is in the upper abdomen and part of the digestive system. The liver cells (hepatocytes) remove and break down products such as harmful chemicals and medicines from the blood making them harmless. Their other functions include production of proteins, enzymes, bile, and blood clotting factors; storage of vitamins; and regulating blood sugar levels and hormones.

The two bean-shaped kidneys are below the ribs, either side of the backbone. They are made up of many functioning units (the nephrons) that each have a filter (the glomerulus), which remove waste products and excess fluid from the blood and make urine. They also produce hormones that regulate blood pressure and red blood cell production, and produce a form of vitamin D.

What are Liver Function and Kidney Function Tests?

Liver function and kidney function tests check that these vital organs are working properly and that there are no signs of damage or disease. They can also indicate disease outside of the liver and kidneys. Any deviation from the normal range can be detected by measuring blood levels of the different substances produced in the liver and kidneys. Early detection and subsequent treatment of abnormalities are key to keeping disease and other problems from either arising or progressing to serious conditions.

What are the main Liver Function and Kidney Function Tests?

A liver function test typically measures:

• Enzymes made by the liver, namely alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transpeptidase (GGT). Some of these enzymes also occur in other tissues
• Bilirubin, a waste product excreted in bile, formed when the liver breaks down haemoglobin in red blood cells
• Proteins made in the liver (albumin and globulin) and the total protein in the blood.

Sometimes, the blood clotting factor prothrombin is also measured (this is not included on our panel).

A Kidney function test includes:

• Electrolytes (ions or electrically charged particles), namely sodium, potassium, chloride, and bicarbonate
• Urea, a waste product excreted in urine, formed from the breakdown of proteins
• Creatinine, a waste product excreted in urine, made by muscles.

The rate blood is filtered by the kidney glomeruli in the process of urine production (the estimated glomerular filtration rate; eGFR) is also measured.

Why is a Liver Function and Kidney Function Test important?

The results of these function tests indicate the general health status of the liver and kidneys, as well as other organ function. They can be used for investigation of symptoms, diagnosis of disease, monitoring liver and kidney function, monitoring the effect of medicines and other treatments, and to screen for signs of liver or kidney disease.

Liver function tests check blood levels of enzymes and proteins. The enzymes ATL, AST, and ATL helps break down amino acids and proteins into energy for the liver cells. GGT helps the liver break down medicines and toxins. Albumin and globulin are important transport molecules needed for many functions including the body's immune (defence) system. Bilirubin is excreted via the bile in stools.

Kidney function tests check blood levels of the electrolytes, urea, and creatinine. The electrolytes are important for normal body function, including nerve and muscle function (sodium and potassium), body water content (sodium and chloride), and the acid-base (pH) balance in blood and tissues (chloride and bicarbonate). Almost all urea and creatinine are filtered out of the blood and excreted by the kidneys; therefore, blood urea and creatinine levels are good indicators of how well the kidneys are working.

Please note that on our postal kit panel, we cannot measure Potassium levels, as the changes in the biochemistry of the sample while in transit will render this reading unreliable. There may be minor changes in the biochemistry of the sample affecting the other electrolytes, but the doctor is able to take this into account when providing an interpretation of your results.

Who should monitor their Liver Function and Kidney Function?

Liver function tests check for disease or damage to the liver. The tests are performed if you present to your doctor with signs and symptoms that potentially suggest a problem with your liver. These include a yellowish skin and eye whites, tender abdomen, nausea/vomiting, diarrhoea, dark urine, colour change to stools, and tiredness. These tests are also important if you have a family history of liver disease, have a diagnosis of liver disease (e.g., cirrhosis, gallstones, or cancer), take medicines or recreational drugs that cause liver toxicity, drink alcohol excessively, or have been exposed to or have hepatitis virus.

Likewise, kidney function tests assess the kidneys for disease or damage. Your doctor may request these if you have signs and symptoms of kidney disease, such as swollen wrists, ankles, thighs, stomach, or face; back pain; urine that is an abnormal colour, bloody, or foamy; reduction in the amount of urine during urination; or change in frequency of urination. These tests are also important if you have risk factors affecting kidney function, including diabetes, high blood pressure, cardiovascular disease, obesity, or a family history of kidney disease, have kidney disease, receive dialysis, or use recreational drugs.

How to test for Liver Function and Kidney Function?

These liver function and kidney function tests are done using a blood sample from a vein. A test kit is supplied by The Online Clinic for you to take to a partner phlebotomy service convenient for you. Your blood sample is then sent to our laboratory in the pre-paid envelope. Test results are sent to one of the doctors at The Online Clinic, who will provide an interpretation of your results. You will also receive a PDF of your full lab report. Please note that self-collect blood samples are not valid for this assay.

What do Liver Function Test and Kidney Function Test results indicate?

The results of your liver function and kidney function tests are interpreted considering your signs and symptoms, risk factors for disease, and other medical conditions. These tests indicate whether the liver and kidneys are functioning normally or if there is liver and/or kidney dysfunction, damage or disease.

With regard to liver function tests, raised levels of ALT, AST, ALP, and GGT indicate liver inflammation and cell death. GGT is particularly useful in detecting damage caused by medicines/other drugs and alcohol, while increased ALP suggests blocked bile ducts. A raised bilirubin level typically occurs when bile ducts are blocked (e.g., by gallstones), preventing bile passage to the intestine, but may also occur in cases of excess breakdown of red blood cells. Albumin levels tend to be low when there is extensive liver cell death, malnutrition, kidney disease, and inflammatory conditions. Low globulin levels may mean liver or kidney disease; high levels indicate infection, inflammatory or immune disorders or certain blood cancers.

Regarding kidney function tests, the electrolytes sodium, potassium, chloride, and bicarbonate may each increase or decrease for many reasons and any changes are often linked. Problems with kidney function can cause an electrolyte imbalance that can seriously affect the fluid balance and pH balance of blood and tissues. Raised urea and/or creatine levels indicate kidney damage, disease or failure, a decrease in blood supply to the kidneys (e.g., narrowing of the renal artery), or an obstruction to the flow of urine (e.g., kidney stones or prostate problems). Increased creatinine levels may also suggest muscle damage.

What are normal Liver Function Test and Kidney Function Test results?

The levels of the different factors measured in your blood are compared with their reference range, which indicates the minimal and maximal levels considered to be normal. Reference ranges may slightly vary between laboratories. Your doctor will let you know if your results are within the normal range or if they suggest liver or kidney dysfunction, damage or disease or another condition.

How to maintain or achieve good Liver Function and Kidney Function

To keep or improve the health of your liver and kidneys:

• Maintain healthy life style habits, with balanced meals low in saturated fat, regular exercise, keeping a healthy body weight, stopping smoking, and by drinking alcohol moderately
• Your kidneys will particularly benefit from drinking plenty of fluids, and controlling blood sugar levels and blood pressure; avoiding exposure to hepatitis virus (e.g., close contact with infected people) and the avoidance of recreational drugs will benefit the liver
• You should have regular liver and kidney function tests if you are at high risk of liver or kidney disease

Reviewed by: Dr Loraine Haslam MBBS, DRCOG, DFSRH, LoC SDI, LoC IUT, MRCGP
GMC registration number: 4524038
Date: 1 March 2024
Next review: 28 February 2026
All UK registered doctors can have their registration checked on
The Medical Register at the GMC website.