The Lab Library

SDMA is a blood marker of how well the kidneys are filtering. It rises earlier than creatinine — often while a pet still looks completely well — so a value creeping up over successive tests, even one still inside the reference range, is the signal worth watching rather than any single reading.

Creatinine is a muscle waste product cleared by the kidneys, so a raised level points to reduced kidney filtration. It's a late signal — it only climbs once a large share of kidney function is already lost — so it's read alongside SDMA and urine concentration, and the trend over time matters more than a single figure.

Urea is a protein waste product the liver makes and the kidneys clear, so a raised level can reflect reduced kidney filtration. But it's easily swayed by hydration, diet and gut bleeding, so it's interpreted alongside creatinine and SDMA rather than on its own.

Phosphorus is a mineral balanced by the kidneys, gut and bone. It tends to rise as kidney disease advances, and keeping it in the lower part of the range is a central goal of kidney care — so a climbing phosphorus in a kidney patient is an important, actionable signal.

Urine specific gravity measures how concentrated the urine is — how well the kidneys are holding on to water. Dilute urine alongside rising blood kidney markers is far more meaningful than either finding alone, which is why a urine sample is essential to interpreting kidney results.

The UPC ratio measures how much protein is leaking into the urine, corrected for how concentrated that urine is. Persistent proteinuria is one of the strongest predictors that kidney disease will progress, so a UPC that stays above the normal range — or drifts upward over repeated samples — is worth acting on early, often before other kidney markers move.

Potassium is held within tight limits because both high and low levels directly affect the heart and muscles. The kidneys and adrenal glands are its main regulators, so an abnormal value points there — and a markedly high potassium, in particular, can be a medical emergency.

Sodium tracks the balance between salt and water in the body — so it's really a marker of water balance as much as salt. It shifts with hydration, kidney handling and some hormonal conditions, and both high and low values are read in that context rather than as 'too much' or 'too little' salt.

Chloride moves largely in step with sodium and helps describe the body's acid-base balance, so it's interpreted alongside the other electrolytes rather than alone. Its main independent value is in acid-base assessment, where a chloride out of step with sodium is the informative finding.

The sodium-to-potassium ratio is a derived value that acts as a screening flag: a low ratio (classically under 27) is the recognised prompt to consider Addison's disease. It's a red flag to investigate, not a target to optimise.

FGF-23 is a phosphate-regulating hormone that often rises before creatinine in feline kidney disease. IRIS guidance uses it to decide which cats with early CKD benefit from dietary phosphate restriction, so a value climbing toward the upper limit — even before creatinine moves — is worth discussing with your vet.

Klotho is a protective protein, made largely by the kidneys, that links kidney function with inflammation, bone and musculoskeletal health — and lower levels track chronic kidney disease and ageing. It is a research assay with no routine clinical reference range in dogs or cats, so it is surfaced as an emerging signal only.

Cystatin C is a small protein filtered freely by the kidneys, so it corroborates early kidney decline alongside SDMA and creatinine — and, unlike creatinine, it is not swayed by muscle mass. Canine and feline reference intervals remain lab-dependent, so it is read as a corroborating trend rather than against a fixed threshold.

ALT is an enzyme that lives inside liver cells and leaks into the blood when those cells are stressed or damaged, so a raised ALT points towards the liver. A single mild elevation is common and often passes; a sustained or rising level across repeat tests is the more meaningful signal, and the height of the number does not reliably tell you the cause.

ALP is an enzyme that rises with liver and bile-system changes, but in dogs it also climbs with steroids, some medicines, bone growth and hormonal conditions — so it's quite non-specific and is read together with ALT and GGT rather than alone. In cats, by contrast, almost any ALP rise is meaningful.

GGT is an enzyme that points more specifically at the bile system than ALP, so a rise here helps separate liver-and-bile changes from the bone and steroid effects that also lift ALP. It's usually read as a partner to ALP and ALT rather than on its own.

Bilirubin is the pigment left over when old red blood cells are broken down; the liver processes it and sends it out in bile. A clear rise causes the yellow tinge of jaundice and points to one of three things — accelerated red-cell breakdown, liver disease, or blocked bile flow — and always warrants prompt veterinary attention.

Albumin is the main protein made by the liver; it holds water inside blood vessels and carries many substances around the body. A low albumin is the meaningful finding — it can reflect reduced liver production, loss through the gut or kidneys, or inflammation — which is why it helps tie several body systems together.

Total protein is albumin plus all the globulins (mostly antibodies) added together. Because two very different proteins are combined, the total is only the headline — it's the split between albumin and globulin that tells the story, so both unusually high and low values are worth understanding.

AST is an enzyme found in both liver and muscle, so it's read alongside ALT to judge whether a rise is coming from the liver or from muscle. When AST and ALT climb together it points to the liver; when AST rises with muscle markers, it points to muscle.

Bile acids test how well the liver is actually working — its function — rather than whether liver cells are leaking enzymes. That means they can flag reduced liver function or a portosystemic shunt even when ALT and ALP look normal, which makes them a powerful second-line liver test.

Glucose is blood sugar, central to screening for diabetes. A single high reading is hard to interpret on its own — stress alone can raise it, especially in cats — so a persistent trend matters more than one value, and fructosamine is used to confirm the picture.

Fructosamine reflects the average blood glucose over the previous two to three weeks, so it sees straight through the momentary spikes — especially stress spikes in cats — that make a single glucose reading hard to trust. It's the number used to confirm diabetes and to judge whether treatment is working.

T4 (thyroxine) is the main thyroid hormone, and it sets the body's metabolic pace. The direction of an abnormal result points to different diseases in the two species — a low T4 raises underactive thyroid in dogs, a high T4 raises overactive thyroid in older cats — so which way it moves is the whole message.

Unlike in people, cholesterol in dogs and cats is read mainly as a clue to hormonal and metabolic conditions — thyroid disease, Cushing's, diabetes — rather than as a heart-attack risk. So a high cholesterol is a prompt to look at the endocrine system, not the arteries.

Calcium is held under tight hormonal control, so a persistently abnormal value — high or low — is meaningful and points to hormonal, kidney or, less often, cancer-related processes. Both extremes matter, and a truly abnormal calcium usually earns a focused work-up.

Free T4 is the unbound, active fraction of thyroid hormone — the part actually available to the tissues. Because it's less swayed by unrelated illness than total T4, it's used to confirm a thyroid picture that total T4 has raised, and to see past the 'sick euthyroid' trap.

NT-proBNP is a substance the heart muscle releases when it is stretched or strained, so a rising value can flag heart disease before outward signs appear. It's a screening and triage tool — high values prompt imaging (an echocardiogram) rather than a diagnosis on their own.

Troponin is released when heart-muscle cells are injured, so a raised level signals active cardiac stress or damage. It's read alongside NT-proBNP and the physical exam — NT-proBNP reports strain, troponin reports injury — and it's very sensitive, so even small rises are taken seriously.

GDF-15 is a stress signal released by cells under strain, and in humans it is one of the strongest single-marker predictors of frailty and mortality. It is measurable in dogs and rises in preclinical heart disease — but there is no established canine or feline reference range, so it is read as a direction of travel, never judged against a threshold.

B12 is a vitamin absorbed in the lower gut, so a low level can signal a gut or microbiome problem — and, unusually for a lab finding, it's one you can often correct directly with supplementation. That makes a low B12 both a useful clue and an actionable one.

Folate is a vitamin absorbed in the upper gut, so reading it alongside B12 (absorbed lower down) helps pinpoint where in the digestive tract a problem sits. Both extremes carry meaning, and the pattern of the two vitamins together is more useful than either alone.

TLI checks whether the pancreas is producing enough digestive enzymes. A low value is the defining test for exocrine pancreatic insufficiency (EPI) — a treatable cause of weight loss despite a big appetite — so it turns a frustrating, mysterious problem into a manageable one.

The Dysbiosis Index is a quantitative PCR measure of gut bacterial balance from a faecal sample — the validated microbiome test, distinct from consumer wellness sequencing. It gives the gut a single number, but it is read against a laboratory-specific scale rather than a universal reference band.

CRP is a protein that rises quickly with inflammation anywhere in the body and falls as it settles, which makes it an excellent way to track whether an inflammatory process is improving. CRP is the dog's main inflammatory marker — cats use serum amyloid A instead.

Serum amyloid A is the cat's main inflammatory marker — the feline counterpart to CRP in dogs. It rises sharply with inflammation and falls as it resolves, so its trajectory is an excellent way to tell whether an inflammatory process is settling.

The white cell count reflects the immune system's activity. Both high and low values matter, but the total is only the headline — the pattern across the differential (which types of white cell have changed) tells you far more than the number alone.

Neutrophils are the immune system's front-line responders to infection and inflammation, and they are usually the largest part of the white cell count. Shifts here — up or down — help characterise what the total count is reacting to, and a supporting detail called a 'left shift' adds important context.

Haematocrit is the proportion of blood made up of red cells — the body's oxygen-carriers. A low value means anaemia; a high one usually means dehydration or, less often, overproduction. Both ends carry meaning, and the trend and the reticulocyte count tell you what kind of process is at play.

Haemoglobin is the oxygen-carrying pigment packed inside red blood cells, and it tracks closely with the haematocrit. Together they describe how well the blood is carrying oxygen, so a low haemoglobin is essentially another way of measuring anaemia.

Platelets are the tiny cell fragments that form clots to stop bleeding. A very low count raises a genuine bleeding risk and is taken seriously — but in cats especially, platelets often clump in the sample and make the reported number falsely low, so a low result is confirmed before it is believed.

Lymphocytes are the arm of the immune system that handles longer-term and viral responses and makes antibodies. Stress and steroids lower them, so context matters — and a persistent, marked rise is one of the flags that warrants a closer look for a lymphoid disorder.

Monocytes are the clean-up and repair cells of the immune system — they clear debris and sustain longer-running inflammation. A raised count often accompanies a chronic, healing, or tissue-damaging process, so it's read as part of the pattern rather than a diagnosis on its own.

Granulocytes are the front-line infection-fighting white cells — mostly neutrophils, plus eosinophils and basophils. Some analysers report them as a single group; the absolute count is the meaningful figure, and it's interpreted much like the neutrophil count it largely represents.

Globulins are largely antibodies, so a persistently raised value reflects chronic immune stimulation or inflammation, while a low value can signal an antibody or protein-loss problem. Read with albumin, globulin helps tell an immune process from a simple protein leak.

The albumin-to-globulin ratio is a derived value that captures the balance between the liver's main protein and the immune system's antibodies. A falling ratio flags chronic inflammation or an antibody-producing process, and it is followed as a pattern rather than optimised to a target number.

The red cell count is the number of oxygen-carrying cells in the blood, sitting alongside haematocrit and haemoglobin as a measure of oxygen-carrying capacity. A low value indicates anaemia; a high one usually means dehydration or overproduction — and it's read together with the red-cell indices.

MCV is the average size of the red blood cells. Small cells point towards iron issues or chronic disease; large cells often accompany a regenerative response to anaemia. It's one of the red-cell indices used to characterise what type of anaemia is present.

MCH is the average amount of oxygen-carrying pigment in each red blood cell. It's read together with MCV and MCHC to characterise the type of any anaemia, and it tends to track closely with cell size.

MCHC is how tightly packed the oxygen-carrying pigment is inside red cells. A low value suggests a regenerative or iron-poor picture; a high value is almost always a sample artefact, since cells cannot truly be over-filled with pigment.

RDW measures how variable the red cells are in size. A rising value is an early clue that the marrow is releasing a new population of differently-sized cells — as in a regenerative response — so it can flag change before the average indices move.

MPV is the average size of the platelets. Larger, younger platelets can indicate the marrow is actively replacing them — a useful clue when the platelet count is low. In cats this figure is often unreliable because platelets clump so readily.

Serum 25-hydroxyvitamin D is the storage form of vitamin D and, unlike in people, in dogs and cats it comes almost entirely from the diet rather than sunlight. Lower status tracks inflammation, several cancers, and cardiac and kidney disease — but laboratory methods disagree markedly, so there is no settled universal reference band.

The Nu.Q test measures circulating nucleosomes — DNA fragments shed into the blood by cancer cells — as a screen for systemic cancers such as lymphoma and haemangiosarcoma in dogs. It's a screening aid, not a diagnosis: a raised result must be confirmed with imaging or biopsy, and inflammation can raise it too.

TK1 is an enzyme released by rapidly dividing cells, so a raised serum level flags high cell turnover. Paired with CRP it forms a screening index used to look for occult cancer in apparently-healthy dogs — but it is read on lab-specific cut-offs, and it signals proliferation, never a diagnosis.

TSH is the pituitary's instruction to the thyroid, so it moves in the opposite direction to thyroid hormone. In dogs it is the key partner to T4 for confirming an underactive thyroid — a low T4 with a high TSH is the classic combination — and it's the test that helps separate true hypothyroidism from illness-related dips.

Triglycerides are the main fat carried in blood. The commonest reason for a high result is simply a recent meal, so a fasted sample is essential — but a genuinely high fasted triglyceride is worth taking seriously, because it is linked to pancreatitis and points towards hormonal and metabolic conditions.

Cortisol is the body's main stress hormone, and a single resting measurement is almost never diagnostic — it fluctuates far too much. Adrenal disease is diagnosed with dynamic tests (ACTH stimulation, LDDST) that watch how cortisol responds to a challenge, which is what makes the result interpretable.

Ionised calcium is the free, biologically active fraction of calcium — the part that actually does the work. Because total calcium is heavily influenced by albumin, ionised calcium is the measurement that confirms whether an abnormal total is real, and it's the one that matters clinically.

Magnesium is a cofactor for hundreds of enzymes and is essential for nerve, muscle and heart function. Because almost all of it sits inside cells, the blood level understates true status — but a low magnesium matters, not least because it can make a low potassium or calcium refuse to correct.

Pancreatic lipase immunoreactivity is the most specific blood test for pancreatitis, because it measures lipase made only by the pancreas — unlike the old catalytic lipase and amylase, which pick up enzymes from elsewhere. It supports the diagnosis but doesn't stand alone: imaging and clinical signs complete the picture.

Lipase is the fat-digesting enzyme, measured on most standard chemistry panels. Traditional lipase is poorly specific for pancreatitis because other tissues contribute and kidney disease raises it — the newer DGGR method performs much better, and pancreatic lipase immunoreactivity is better still.

Amylase is the starch-digesting enzyme, historically measured to investigate pancreatitis. It is now regarded as a poor test for that purpose — too many non-pancreatic sources and too easily raised by kidney disease — and it has been largely superseded by pancreatic lipase immunoreactivity.

Faecal testing screens for intestinal parasites, and modern antigen tests detect worm proteins rather than eggs — which matters because worms shed eggs intermittently, so traditional flotation misses infections. Antigen and flotation together catch considerably more than either alone.

GLDH is a liver enzyme held inside the mitochondria, deep within liver cells — so it only escapes when injury is more substantial than the surface leakage that raises ALT. Common on UK and European panels, it is a more liver-specific marker and a useful complement to ALT.

Ammonia is a gut-derived toxin that a healthy liver converts to urea before it reaches the brain. A raised blood ammonia means that detoxification has failed — pointing to a portosystemic shunt or significant liver failure — and it correlates with the neurological signs of hepatic encephalopathy.

Eosinophils are the white cells that respond to parasites and allergic inflammation, so a raised count classically points to worms, fleas, or allergic disease. A low count is usually just the body's stress response and rarely means anything on its own.

Basophils are the rarest white cells, involved in allergic and parasitic responses. They are so scarce that a low count is meaningless, and even a raised count is uncommon — when it does occur it usually travels with eosinophils and points towards parasites, allergy, or (classically) heartworm.

Reticulocytes are young red blood cells, and counting them answers the single most important question about any anaemia: is the bone marrow responding? A high count means a regenerative anaemia (blood loss or destruction); a low one means the marrow isn't keeping up.

The NLR divides neutrophils by lymphocytes to capture the balance between the immune system's front line and its longer-term arm. It's a cheap, emerging marker of systemic inflammation and stress that has shown prognostic promise — but it is highly non-specific, and a routine stress response raises it just as readily as disease.

Iron studies exist to answer one question: is an anaemia caused by true iron deficiency, or by chronic inflammation? Both lower serum iron, but they behave differently — iron deficiency raises the carrying capacity (TIBC) and empties the stores (ferritin), while inflammation lowers capacity and raises stores.

Allergen-specific IgE blood panels do not diagnose allergy — atopic dermatitis is a clinical diagnosis made by excluding other causes of itch. Their real purpose is to select which allergens to include in immunotherapy once that diagnosis is already made, which is a genuinely useful but much narrower job.

This derived ratio compares two kidney markers that behave slightly differently, which can help suggest whether a raised urea is coming from dehydration, a gut bleed, or the kidney itself. It's a soft supporting clue in pets — much less reliable than in human medicine — and never a diagnosis.

Calcium and phosphorus are regulated together, so they are read as a pair. In kidney disease the calcium × phosphorus product matters because when both run high, minerals can deposit in soft tissues — including the kidneys themselves — which is a key reason phosphate control is so central to CKD care.

The UCCR measures cortisol in urine, corrected for concentration, giving an integrated picture of cortisol output rather than a single stressed snapshot. It is a very sensitive screen for Cushing's disease — excellent at ruling it OUT, but poor at ruling it in, because stress alone raises it.

Bicarbonate is the body's main buffer against acid, so total CO₂ on a chemistry panel is essentially a measure of acid-base balance. A low value usually means metabolic acidosis — acid accumulating or bicarbonate being lost — which is common in kidney disease, diabetes and severe diarrhoea.

The anion gap is a calculated value that estimates the 'unmeasured' acids in blood. Its main job is to sort metabolic acidosis into two categories — a high gap means acid has been added (ketones, lactate, toxins), a normal gap means bicarbonate has been lost — which points to very different causes.

A urinalysis is three tests in one — concentration, a chemical dipstick, and microscopic sediment — and it transforms the meaning of blood results. Without a urine sample, kidney blood markers can only ever be half-interpreted, which is why a urinalysis is the most under-requested test in veterinary medicine.

Cognitive decline in ageing pets isn't measured by a blood test — it's screened with a validated owner questionnaire. In dogs the CCDR (Canine Cognitive Dysfunction Rating) turns everyday behaviour changes into a score that flags whether canine cognitive dysfunction ('dog dementia') is likely, so it can be recognised and managed early.

Genetic panels report predisposition, not diagnosis — carrying a variant is not the same as having the disease. Their two genuinely actionable uses are drug-safety variants like MDR1, which change medication choices today, and informed breeding decisions.