Liver Function

Total protein measures the combined amount of all the proteins circulating in your blood, which fall into two main groups: albumin and globulins. This test provides a broad overview of your body's protein status, reflecting both how well your liver is producing proteins and how effectively your kidneys are retaining them. Understanding your total protein level matters because blood proteins perform an extraordinary range of jobs. They transport hormones, vitamins, and medications to where they are needed, help your blood clot when you have a cut, fight off infections through antibodies, and maintain the fluid balance between your blood vessels and surrounding tissues. A healthy total protein level is a reassuring sign that these essential systems are working as they should. Your liver is the main protein factory in your body, responsible for producing albumin and many of the globulins that circulate in your blood. Think of it like a well stocked warehouse: as long as the liver is healthy and you are getting enough protein from your diet, the shelves stay full. Meanwhile, your kidneys act as quality-control filters, making sure that useful proteins stay in the blood rather than being lost in your urine. The balance between production by the liver and retention by the kidneys determines your overall total protein level. Several factors can influence your reading. Dehydration can temporarily concentrate your blood proteins, making the total appear higher than it truly is, while overhydration can have the opposite effect. Your diet plays a role too, prolonged low protein intake can gradually reduce levels. Intense exercise, illness, and certain medications may also cause shifts. If you have been unwell recently, your globulin levels might be temporarily raised as your immune system responds. If your total protein result is higher or lower than expected, your GP can help interpret it by looking at the albumin and globulin breakdown alongside your other results. This gives a much clearer picture of what might be driving any change and whether further investigation would be useful.

Albumin is the most abundant protein in your blood, making up roughly sixty per cent of your total blood protein. This test measures how much albumin is circulating in your bloodstream, and it serves as a valuable indicator of both liver health and overall nutritional status. Healthy albumin levels matter enormously because this protein is a genuine multitasker. It acts as a transport vehicle, carrying hormones, vitamins, calcium, and certain medications through your bloodstream to wherever they are needed. Just as importantly, albumin creates what is known as oncotic pressure, a gentle pulling force that keeps the right amount of fluid inside your blood vessels rather than letting it leak into surrounding tissues. When albumin levels are healthy, your circulation stays well balanced and your tissues receive a steady supply of the substances they need. Your liver produces albumin continuously, releasing it into the bloodstream at a steady rate. From there, it circulates for roughly three weeks before being broken down and replaced. Because your liver makes albumin and your kidneys prevent it from being lost in urine, this marker effectively tells you something about how both organs are performing. It is also what scientists call a negative acute-phase reactant, which means that during periods of inflammation or illness, your body naturally dials down albumin production temporarily, so a lower reading does not always mean something is wrong with your liver. Your albumin level can be influenced by your diet, particularly if protein intake has been low for an extended period. Dehydration can push the reading up slightly because the blood becomes more concentrated, while overhydration can dilute it. Intense physical training, recent illness, surgery, and certain chronic conditions can all cause temporary dips. Pregnancy also naturally lowers albumin due to increased blood volume. If your albumin level comes back outside the expected range, it is worth discussing with your GP. They can look at it alongside your other protein markers, liver enzymes, and kidney function tests to understand the full picture and advise on any next steps.

Globulin refers to a diverse family of proteins in your blood that includes antibodies, transport proteins, and enzymes. This test measures the total amount of globulins circulating in your bloodstream, and it is usually calculated by subtracting your albumin level from your total protein. Knowing your globulin level is important because these proteins are central to two of your body's most critical functions: immune defence and the transport of essential substances. Your antibodies, also known as immunoglobulins, are globulins that recognise and neutralise bacteria, viruses, and other threats. Other globulins carry iron, hormones, and fats through your blood to the cells that need them. A healthy globulin level suggests that your immune system is functioning well and that your transport networks are running smoothly. Your immune cells produce the antibody portion of globulins in response to anything they perceive as foreign, while your liver manufactures many of the transport globulins. Think of globulins as a combined security and logistics team: one division patrols for threats, while the other ensures vital cargo reaches its destination. When your body is fighting an infection or dealing with inflammation, it ramps up globulin production, which is why levels can rise temporarily during illness. Conversely, when the immune system is underperforming, globulin levels may dip. A number of factors can shift your globulin reading. Recent infections, vaccinations, and inflammatory conditions can all cause a temporary rise, as your immune system produces more antibodies. Chronic conditions affecting the liver or kidneys may also influence levels. Dehydration can concentrate your blood proteins and push the result upward, while malnutrition or conditions that suppress the immune system may lower it. Your GP will often look at the balance between albumin and globulin, known as the A/G ratio, because this can provide additional insight into what might be happening. If your globulin level is outside the normal range, a conversation with your GP is a sensible next step. They can consider it alongside your albumin, total protein, and any relevant clinical signs to determine whether further investigation would be helpful.

ALT (Alanine Transferase, sometimes written ALAT) is an enzyme found almost exclusively inside liver cells. Because it is so liver-specific, it is widely regarded as the single most reliable marker for detecting stress or damage to liver tissue. When liver cells are healthy and intact, very little ALT leaks into the bloodstream. When they are irritated, inflamed, or dying, ALT spills out, and the blood level rises. This is why ALT is one of the first markers to move when something is putting pressure on your liver, often before you notice any symptoms. A helpful way to picture ALT is to think of it as a warning light on a dashboard. Your liver is an extraordinarily busy organ, processing everything you eat, drink, and absorb, producing the proteins your body depends on, and filtering out toxins. Inside its cells, ALT plays a role in converting amino acids into glucose, a process called gluconeogenesis that helps keep your blood sugar steady between meals. As long as the cells stay intact, ALT does its work quietly. If the cell membrane is damaged, ALT escapes into the blood, and the level you see on your result rises accordingly. ALT is sensitive to a broad range of common lifestyle factors. The most frequent causes of mildly raised ALT are non-alcoholic fatty liver disease (often linked to excess weight, insulin resistance, and a diet high in refined carbohydrates), alcohol above sensible limits, and certain medications, including statins, paracetamol at high doses, some antibiotics, and anti-epileptics. Supplements are an underappreciated contributor: high-dose vitamin A, green tea extract, kava, and some bodybuilding and weight-loss supplements are well documented to raise ALT. Viral hepatitis (A, B, C, E), autoimmune liver conditions, and muscle damage from very intense exercise can also push it up. ALT is usually interpreted alongside AST and GGT to clarify the source of the problem. If your ALT is raised, your GP will consider the context, your alcohol intake, medications, supplements, weight changes, and other liver markers, before recommending next steps. Mild, stable elevations are often lifestyle-related and respond well to changes over a few weeks or months. Persistent or significant elevations may warrant further investigation, including a liver ultrasound or hepatitis screening.

ALP (Alkaline Phosphatase) is an enzyme produced by several tissues around the body, but two sources matter most: the liver (specifically the cells lining the bile ducts) and bone (specifically the cells that build new bone, called osteoblasts). Smaller amounts come from the intestines and placenta. Because ALP has two main origins, interpreting a raised result depends entirely on working out which source is responsible, and that is where other markers on your panel become essential. A useful way to think about ALP is as a combined readout from two systems. In the liver, it is concentrated in the tiny ducts that drain bile from the liver to the digestive tract. If those ducts are blocked, inflamed, or pressed upon, the cells lining them are stressed and release more ALP into the blood. In bone, ALP is released whenever bone-building activity is high, during normal childhood and teenage growth, during pregnancy, while a fracture is healing, and in certain bone conditions like Paget's disease. This is why ALP is naturally much higher in growing children and in pregnant women, and why a raised ALP should not be assumed to come from the liver without further thought. The standard way to decide the source is to look at ALP alongside GGT. GGT is a liver-and-bile-duct enzyme, it is not made by bone. So a raised ALP with a raised GGT strongly suggests a liver or bile duct origin, while a raised ALP with a normal GGT points to bone as the source. Other factors can also influence ALP: vitamin D deficiency often causes mild elevations as the body tries to mobilise bone to maintain calcium levels, eating a fatty meal shortly before a blood test can transiently raise ALP from the intestinal form, and certain medications (some antibiotics, anti-epileptics, and hormonal contraceptives) can nudge it up. If your ALP is out of range, your GP will use the rest of your panel, GGT, bilirubin, calcium, vitamin D, and liver enzymes, to work out whether it reflects liver or bile duct activity, normal bone turnover, or something worth investigating further. A low ALP is uncommon and can occasionally reflect zinc deficiency, malnutrition, hypothyroidism, or (rarely) an inherited condition called hypophosphatasia.

AST (Aspartate Transferase, sometimes written ASAT) is an enzyme found inside the cells of several tissues, most significantly the liver, heart, and skeletal muscle, as well as the kidneys and red blood cells. Unlike ALT, which is almost exclusive to the liver, AST is multi-source. That makes it less specific on its own but very informative when interpreted alongside other markers. A raised AST tells you something in the body is releasing the enzyme, the job is to work out which tissue. Inside the cell, AST plays a role in amino acid metabolism, helping to convert amino acids into building blocks for energy and other molecules. It works alongside ALT in the same pathway. When cell membranes are damaged by inflammation, injury, or overuse, AST leaks into the bloodstream. Because it is particularly concentrated in heart and muscle cells, an intense workout, a long run, heavy resistance training, or a muscle injury can raise AST for a day or two after the event, even in someone with a perfectly healthy liver. The real diagnostic power of AST comes from the AST:ALT ratio. Because ALT is liver-specific and AST is multi-source, their relationship gives a pattern. In non-alcoholic fatty liver disease (NAFLD), the ratio is usually less than 1, ALT runs higher than AST. In alcoholic liver disease, the ratio flips: AST is typically more than twice ALT (a ratio above 2), because alcohol preferentially damages mitochondria where a lot of AST is stored. Acute viral hepatitis tends to raise both roughly equally. A marked AST rise with normal or mildly raised ALT often points to muscle rather than liver, for example after a heavy gym session, prolonged exercise, or in rhabdomyolysis. If your AST is raised, your GP will consider the context: recent exercise, alcohol, medications, and the AST:ALT ratio alongside GGT and ALP. In many cases, mild elevations reflect lifestyle factors and resolve on their own. Persistent or marked elevations warrant further investigation to identify the source and underlying cause.

GGT (Gamma-Glutamyl Transferase, often shortened to Gamma GT) is a liver enzyme concentrated in the cells lining the bile ducts and, to a lesser extent, throughout the liver itself. Its main role in the body is to help transport amino acids across cell membranes and to support the production of glutathione, one of your body's most important antioxidants. Clinically, GGT is one of the most sensitive markers available for detecting early changes in liver and bile duct health, it often responds to lifestyle pressures well before ALT or AST move. Picture the bile ducts as a network of drainage pipes carrying bile from the liver down into the digestive tract. The cells lining those pipes are rich in GGT. When the liver or bile ducts are irritated, blocked, or under chemical stress, those cells release GGT into the bloodstream. Because GGT is so easily provoked, it acts like an early-warning light, responsive to things that have not yet done enough damage to trigger the more slowly-moving enzymes. That sensitivity is both its strength (early detection) and its weakness (it can rise for reasons that turn out to be benign). The factor GGT is most famously sensitive to is alcohol. Even moderate regular drinking can push GGT up, and it typically comes back down within a few weeks of meaningfully reducing intake. This makes GGT a useful and honest feedback signal, and it responds quickly enough that many people find the change encouraging. GGT is also raised by non-alcoholic fatty liver disease (often linked to excess weight, insulin resistance, and a diet high in refined carbohydrates), by bile duct obstruction or inflammation, and by a number of medications, including certain anti-epileptics, some sleep medications, warfarin, and oral contraceptives. Herbal supplements can also be a factor. GGT is almost always interpreted alongside ALP to distinguish liver or bile duct problems from bone problems (GGT is not made by bone), and alongside ALT to work out whether the liver as a whole is inflamed. If your GGT is raised, your GP will consider the context, your alcohol intake, medications, weight, and other liver markers. Many raised GGT results respond well to specific, achievable lifestyle changes. Where the elevation persists or is significant, further investigation such as a liver ultrasound may be appropriate.

Bilirubin is a yellow-orange pigment produced when your body breaks down old red blood cells. Red cells live for around 120 days, and as they are retired, their haemoglobin is dismantled and the iron is recycled. What is left over becomes bilirubin. The liver picks it up from the blood, chemically modifies it so that it dissolves in bile, and sends it out into the digestive tract, where it contributes to the characteristic brown colour of stools. Measuring bilirubin tells you how well this whole recycling and clearance chain is working. Bilirubin initially circulates in an "unconjugated" form, insoluble in water and carried attached to albumin. The liver converts it into a soluble "conjugated" form that can be excreted in bile. Bilirubin can therefore accumulate for three broad reasons: too much red cell breakdown (haemolysis), the liver struggling to process it, or a blockage downstream preventing bile from leaving the liver (gallstones, a stricture, or tumour in the bile ducts). When bilirubin builds up significantly, the pigment deposits in the skin and the whites of the eyes, causing the yellow tinge known as jaundice. One thing worth knowing is that a mild, isolated rise in bilirubin is extremely common and is very often caused by Gilbert's syndrome. Gilbert's is a harmless inherited variation in which the liver enzyme that conjugates bilirubin works slightly less efficiently. It affects roughly 5% of adults, runs in families, and causes no symptoms other than occasional mild jaundice. Levels characteristically fluctuate and can rise during fasting, illness, dehydration, or poor sleep. Because Gilbert's is so common, a mildly raised bilirubin picked up incidentally, with completely normal ALT, AST, GGT, ALP and a normal full blood count, is almost always Gilbert's rather than liver disease. The pattern across your other markers separates the causes. Raised bilirubin with raised ALT and AST suggests liver cell damage, raised with ALP and GGT suggests bile duct obstruction, raised with low haemoglobin, high LDH and low haptoglobin suggests haemolysis. If your bilirubin is raised, your GP will look at the whole picture to decide whether any further investigation is needed.

Sex hormone binding globulin, known as SHBG, is a protein produced mainly by your liver that acts as a transport vehicle for sex hormones, particularly testosterone and oestrogen, as they travel through your bloodstream. While SHBG is not a hormone itself, it plays a crucial role in determining how much of your sex hormones are actually available for your body to use. Understanding your SHBG level adds important context to your testosterone and oestrogen results and can reveal subtleties that those markers alone might not show. Imagine SHBG as a fleet of taxis carrying passengers around a city, the hormones are the passengers, and while they are in the taxi, they cannot get out and do their jobs. Only the hormones that are free, not bound to SHBG, can enter your cells and have an effect. When SHBG levels are high, more hormones are bound up and fewer are available to tissues; when SHBG is low, more hormones circulate freely. This means that even if your total testosterone or oestrogen looks perfectly normal, your SHBG level could mean you effectively have too much or too little active hormone reaching your cells. Your body adjusts SHBG production in response to a variety of signals, making it a sensitive barometer of metabolic health. A number of factors can influence your SHBG levels. Oestrogen tends to increase SHBG production, which is why women generally have higher levels than men and why hormonal contraceptives can raise SHBG significantly. Conversely, carrying excess body weight, particularly around the abdomen, tends to lower SHBG, as does insulin resistance. Thyroid function also plays a part, an overactive thyroid can push SHBG up, while an underactive thyroid can bring it down. Age, liver health, and certain medications further contribute to the picture. If your SHBG level is outside the expected range, your GP can look at it alongside your free and total sex hormone levels to assess whether your hormonal balance is working well for you.