How to Read Your Pet's Blood Test Results

You get handed a printout with thirty abbreviations and a column of numbers, some flagged with an H or an L. Your vet explains it, you follow about half, and by the time you're in the car you've lost the thread.

Here's a plain-English guide to what the main values mean. This is to help you follow the conversation, not to replace it — interpretation depends on the whole picture, and a single flagged value out of context is often meaningless.

Two panels, usually

The haematology (CBC) looks at blood cells.

The biochemistry looks at organ function and chemistry.

Most vets run both, plus urinalysis, which is essential and sometimes skipped.

The blood cell panel

Red blood cells / haematocrit (HCT or PCV) / haemoglobin

How much oxygen-carrying capacity there is.

• Low = anaemia. Causes include blood loss, destruction of red cells, chronic kidney disease, chronic inflammatory disease, or bone marrow problems.
• High = usually dehydration (the blood is concentrated), occasionally a genuine overproduction.

White blood cells (WBC)

The immune cells. The breakdown matters more than the total.

• Neutrophils — raised with bacterial infection, inflammation, stress, or steroid effect
• Lymphocytes — raised in some viral disease and certain leukaemias; low with stress or steroids
• Eosinophils — raised with parasites and allergic disease
• Monocytes — raised in chronic inflammation

A raised white count means the body is responding to something. A very low count can indicate overwhelming infection or bone marrow suppression, and is more concerning than a high one.

Platelets

Involved in clotting. Low platelets mean bleeding risk. Note that in some breeds, particularly Cavalier King Charles Spaniels, platelets can appear low as a harmless breed characteristic.

The biochemistry panel

Kidney values

• Urea (BUN) — raised with reduced kidney function, dehydration, a high-protein meal, or bleeding into the gut. Not specific on its own.
• Creatinine — a better kidney marker, but insensitive. It doesn't rise until a substantial proportion of kidney function is already lost.
• SDMA — a newer marker that rises considerably earlier than creatinine. Worth asking for in older animals.
• Phosphorus — rises in kidney disease, and controlling it is a key part of managing it.

Critical point: kidney values cannot be properly interpreted without urine specific gravity. Concentrated urine with mildly raised urea usually means dehydration. Dilute urine with raised kidney values points to kidney disease. Without the urine test, you're guessing. Ask whether it was done.

Liver values

• ALT — released from damaged liver cells. Raised suggests liver cell injury.
• ALP — raised in liver disease, bile duct problems, steroid use, Cushing's, and normally in growing animals (it comes from bone too).
• GGT — more specific for bile duct problems
• Bilirubin — raised causes jaundice. From liver disease, bile obstruction, or red cell destruction.
• Albumin — made by the liver. Low with liver failure, protein-losing gut or kidney disease, or severe inflammation.
• Bile acids — a functional test, usually run separately, that assesses how well the liver is actually working

Raised liver enzymes are common and often not serious on their own. They indicate the liver has noticed something, not necessarily that the liver is failing.

Glucose

• High — diabetes, or stress. This matters in cats — stress alone can raise a cat's blood glucose substantially, so a single high reading does not diagnose diabetes. A fructosamine test, which reflects average glucose over the previous two to three weeks, distinguishes them.
• Low — a genuine emergency in a collapsed animal. Causes include sepsis, liver failure, certain tumours, and xylitol poisoning.

Proteins

• Total protein, albumin, globulin. Raised globulins suggest chronic inflammation or immune stimulation. Low albumin has several serious causes.

Electrolytes

• Sodium, potassium, chloride. High potassium is dangerous and is the key concern in a blocked cat. A low sodium-to-potassium ratio raises suspicion of Addison's disease.
• Calcium — high calcium is important, as it can be associated with certain cancers, kidney disease and parathyroid problems.

Thyroid

• T4 — high in feline hyperthyroidism, low in canine hypothyroidism. Note that non-thyroidal illness can suppress T4 in dogs, causing false lows, so results are interpreted alongside clinical signs and sometimes free T4 or TSH.

Pancreas

• Amylase and lipase are unreliable for diagnosing pancreatitis. Specific tests — canine or feline pancreatic lipase — are much better.

Why "within normal range" isn't the full answer

Reference ranges are derived from populations and are deliberately wide. They typically cover the middle 95% of healthy animals — which means some healthy animals fall outside them, and an individual can change substantially while remaining inside them.

A creatinine that has moved from 80 to 140 is a significant change, even if both numbers are technically normal. Without a previous result, that change is invisible.

This is the argument for baseline blood work while your pet is healthy. It converts a wide population range into a personal one, and it's the single most useful thing you can do to make future results meaningful.

Ask for a copy of every set of results and keep them. Compare over time. Vets do this, but only with the results they have — if you've changed practice or moved, they may not have the earlier ones.

Questions worth asking

• "Which values are you most concerned about, and why?"
• "Is this a big change from last time?" — and if there's no last time, "should we get a baseline for future comparison?"
• "Was urine tested as well?"
• "Could any of this be explained by dehydration, stress, or a recent meal?"
• "Does this need repeating, and when?"
• "Does this change what we do, or is it something to monitor?"

What blood tests don't show

Plenty. Blood work is a broad screening tool, not a comprehensive scan.

It will often not detect: early cancer, arthritis, dental disease, most gastrointestinal disease, heart disease, or many neurological conditions. Normal bloods in a sick animal do not mean nothing is wrong — they mean the problem lies elsewhere, which is itself useful information.

The practical habit

Ask for a copy every time. Keep them in one place, in date order.

A folder or a phone album works just as well. The point is that the second result is far more informative than the first, and the fifth is more informative still — but only if you kept them.