Liver function test and kidney function test are both slightly misleading names. Most of a liver panel measures damage rather than function, and the central number on a kidney panel is a waste product whose level depends as much on your build as on your kidneys. Once you know which line is telling you what, both reports become much easier to read.
The liver panel
The enzymes are an injury signal
Liver cells contain enzymes. When cells are inflamed or dying, those enzymes leak into blood and the level rises. That tells you cells are being damaged; it does not tell you how well the organ is working.
- SGPT, also written ALT, sits mainly in the liver, so it is the more specific of the two.
- SGOT, also written AST, is also present in heart and skeletal muscle and in red cells. A hard gym session, a muscle injury or a difficult blood draw can raise it with a perfectly healthy liver.
The relationship between them is a clue. An AST more than twice the ALT points towards alcohol-related liver injury. An ALT higher than the AST is the usual pattern of fat in the liver, the condition renamed in 2023 from non-alcoholic fatty liver disease to metabolic dysfunction-associated steatotic liver disease, or MASLD. It is now the most common reason for a mildly abnormal liver panel in an otherwise well adult, and it travels with insulin resistance, high triglycerides and weight around the abdomen rather than with alcohol.
ALP and GGT are about bile flow
Alkaline phosphatase (ALP) rises when bile drainage is obstructed. It also comes from bone, and rises normally in growing children and in pregnancy from the placenta. GGT is what separates those: a raised ALP with a raised GGT points at the biliary system, while a raised ALP with a normal GGT points at bone. GGT is also sensitive to alcohol and to several medicines.
Bilirubin, and the harmless cause
Bilirubin comes from the breakdown of red cells and is reported as total, direct and indirect. A raised direct fraction suggests the liver or bile ducts are struggling to excrete it. A raised indirect fraction points either at red cells breaking down faster than usual, or at Gilbert's syndrome.
Gilbert's syndrome is an inherited, entirely benign difference in how bilirubin is processed. It affects a few per cent of people, shows up as a mildly raised indirect bilirubin with every other liver value normal, and becomes more obvious when you are fasting, unwell, dehydrated or under strain. It needs no treatment. It is worth recognising precisely because it otherwise gets re-tested for years.
The lines that do measure function
Albumin is made by the liver, and a falling albumin over months suggests reduced synthetic capacity. Prothrombin time or INR reflects clotting factors the liver produces, and is one of the more sensitive markers of serious impairment. Total protein sits alongside them.
This is why enzymes alone can mislead in both directions. In advanced cirrhosis, where there are fewer cells left to leak, ALT and AST can be normal or even low while the liver is failing.
The kidney panel
Creatinine is filtered, but it is also produced
Creatinine is a waste product of muscle metabolism, cleared almost entirely by the kidneys. That makes it a good filtration marker with one large caveat: how much you produce depends on how much muscle you carry.
A small, elderly, frail woman can lose a substantial share of her kidney function with a creatinine still sitting inside the printed range. A young man who lifts weights can sit slightly above it with completely normal kidneys. The number is read differently for different bodies, which is exactly the problem eGFR exists to solve.
eGFR, and why one reading is not a diagnosis
Estimated glomerular filtration rate converts creatinine into an estimate of filtration, adjusted for age and sex, using the 2021 CKD-EPI equation that removed the older race coefficient. An eGFR below 60 matters, but chronic kidney disease is defined by an abnormality that persists for at least three months, and a single low reading has many temporary explanations: dehydration, a course of painkillers, a contrast scan, or any acute illness. The correct response to one unexpected result is usually a repeat, not a diagnosis.
Cystatin C is an alternative filtration marker that does not depend on muscle mass, and it is the test to reach for when creatinine cannot be trusted: very low or very high muscle mass, limb loss, or advanced liver disease.
Urea, and the ratio
Blood urea, or BUN, moves with hydration, protein intake, steroid use and bleeding into the digestive tract as well as with kidney function. Read against creatinine it helps separate a kidney that is under-perfused, typically from dehydration, from one that is intrinsically damaged. Uric acid is reported alongside and relates to gout, diet and kidney handling rather than to filtration itself.
The test that finds it earliest, and gets skipped
Damage to the filtering membrane leaks small amounts of albumin into urine long before creatinine moves. A urine albumin test, usually expressed against urine creatinine as a ratio, turns abnormal above 30 mg/g, and in diabetes and high blood pressure it can do so years ahead of any change in the blood tests. It is inexpensive, needs a urine sample rather than a needle, and is the most commonly omitted test in routine diabetes follow-up. International guidance is unambiguous that anyone at risk should have both a filtration estimate and a urine albumin measurement, not one of the two.
Preparation that changes these numbers
- Heavy exercise in the 24 hours before raises creatinine and AST. A creatine supplement raises creatinine independently of kidney function; mention it.
- A large protein meal shortly before the draw lifts urea and creatinine.
- Alcohol in the previous 24 hours affects GGT and triglycerides.
- Painkillers of the anti-inflammatory type, taken regularly, affect kidney values.
- Supplements matter more than people expect. Herbal preparations, weight-loss products, high-dose vitamins, protein powders and liver tonics are a genuine cause of raised enzymes. List everything you take, prescribed or not.
What a mildly abnormal result usually means
A single mild enzyme rise in someone who feels well is common, and fatty liver explains most of them. What it deserves is a repeat after six to eight weeks with attention to weight, alcohol and sugar in between, alongside your doctor's judgement on whether anything further is needed. Yellowing of the eyes or skin, dark urine, pale stools, persistent vomiting, swelling of the legs, a sharp fall in urine output or enzymes several times the upper limit are a different matter, and belong in front of a doctor promptly rather than in a repeat test.
Both panels sit on almost every package we run, and the tests are grouped under liver and kidney on the test page. The Kidney Health Profile is the fuller version for anyone with diabetes or high blood pressure, and a sample can be collected at home. As always, the report goes to the doctor who knows the rest of your history.
- Liver
- Kidney
- Reading reports
