You Don't Need to Understand All of It. But You Should Know These Five.
Blood panels come with dozens of values, abbreviations, and reference ranges. It's overwhelming, and I've already given you a comprehensive breakdown in a previous article. But if you're going to remember just five numbers from your dog's blood work, these are the ones. They tell you the most about your dog's current health and future trajectory, and they're the ones I look at first when a panel lands on my desk.
1. Creatinine (and SDMA)
What it measures: Kidney function
Why it matters: The kidneys are the organs that fail silently. Creatinine is a waste product filtered by the kidneys, and when it rises above the reference range, significant kidney function has already been lost. SDMA (symmetric dimethylarginine) is a newer marker that rises earlier, potentially when only 25% to 40% of function is lost.
What to watch for: Any upward trend over time, even within the normal range. A creatinine that goes from 1.0 to 1.2 to 1.4 over three annual panels is telling a story. Don't wait for it to go "out of range" to take notice. If SDMA is included in your panel and it's above normal, take it seriously even if creatinine looks fine.
What you can do: Monitor water intake, ensure adequate hydration, request urinalysis alongside blood work, and discuss kidney supportive dietary strategies with your vet.
2. ALT (Alanine Aminotransferase)
What it measures: Liver cell health
Why it matters: ALT is an enzyme found inside liver cells. When liver cells are damaged, ALT leaks into the bloodstream. Elevated ALT tells you that something is injuring the liver, whether it's a medication side effect, toxin exposure, infection, or liver disease.
What to watch for: Elevations beyond the normal range, or a trend upward over time. Mild elevations can be caused by medications (phenobarbital, certain NSAIDs, steroids) and may not indicate serious disease. Dramatic elevations suggest more significant liver involvement.
What you can do: Review all medications your dog is taking, minimize unnecessary chemical exposures, maintain a healthy weight (fatty liver disease exists in dogs too), and follow your vet's recommendations for further investigation if ALT is elevated.
3. Total T4 (Thyroxine)
What it measures: Thyroid function
Why it matters: Hypothyroidism is one of the most common and most treatable hormonal conditions in dogs, and it's also one of the most missed. Low T4 leads to weight gain, lethargy, skin problems, and behavioral changes that are routinely attributed to "normal aging."
What to watch for: Values at the low end of normal or below normal. Note that T4 can be suppressed by other illnesses (euthyroid sick syndrome), so a low T4 in a sick dog doesn't necessarily mean hypothyroidism. A low T4 in a dog with compatible symptoms warrants a full thyroid panel (free T4 and TSH).
What you can do: Request that T4 be included in routine blood work for dogs over age five, especially predisposed breeds. If your dog has symptoms compatible with hypothyroidism (lethargy, weight gain, coat changes, recurrent infections), push for thyroid testing even if it's not "standard" at your practice.
4. Hematocrit (HCT / Packed Cell Volume)
What it measures: The percentage of blood that is red blood cells
Why it matters: Hematocrit tells you about your dog's oxygen carrying capacity and is one of the fastest ways to screen for anemia (low) or dehydration (high). Anemia can be caused by chronic disease, blood loss, immune destruction of red blood cells, or bone marrow problems. Dehydration concentrates the blood and pushes hematocrit up.
What to watch for: Values below the normal range (anemia) or above it (dehydration or, rarely, polycythemia). In the context of aging dogs, a slowly declining hematocrit over several panels can indicate chronic disease, kidney disease (the kidneys produce erythropoietin, which stimulates red blood cell production), or nutritional issues.
What you can do: Ensure your dog's diet provides adequate iron and B vitamins. If hematocrit is low, follow your vet's recommendations for further investigation. If it's high and your dog isn't dehydrated, this also warrants evaluation.
5. Blood Glucose
What it measures: Blood sugar level
Why it matters: Elevated blood glucose can indicate diabetes mellitus, Cushing's disease, or stress (stress hyperglycemia is common in dogs at the vet, so a single elevated reading should be interpreted with caution). Low blood glucose can indicate liver dysfunction, Addison's disease, or insulin producing tumors.
What to watch for: Persistent elevation across multiple readings, or elevation accompanied by increased thirst, urination, and appetite. A single elevated reading in a stressed dog at the vet may not be meaningful. If glucose is elevated, checking a fructosamine level (which reflects average blood sugar over the previous two to three weeks) helps distinguish true diabetes from stress related elevation.
What you can do: Maintain a lean body weight (obesity is a risk factor for insulin resistance). If glucose is elevated, discuss follow up testing. If you notice increased thirst and urination at home, mention it to your vet and request glucose and fructosamine testing.
How to Use These Five Numbers
- Get copies of every blood panel. Keep them organized chronologically, either digitally or in a folder.
- Track these five values over time. A simple spreadsheet or even a handwritten chart works. Plot each value at each annual test. The trend matters more than any single reading.
- Know your dog's individual baseline. Every dog's "normal" is slightly different within the reference range. Knowing where your dog typically sits helps you spot meaningful changes early.
- Ask your vet about trends, not just flags. "Is this value trending in a direction that concerns you?" is a better question than "is this normal?"
- Start tracking at age five. For large breeds, earlier. The baseline you establish now is the benchmark that makes future changes detectable.
Knowledge Is Advocacy
You don't need a veterinary degree to be an effective advocate for your dog's health. You need five numbers, the willingness to track them over time, and the confidence to ask your vet "what does this trend mean?" That combination, simple as it is, puts you ahead of the vast majority of dog owners in terms of health awareness. And your dog, who can't read their own blood work, is counting on you to pay attention. These five numbers are your most direct window into what's happening inside their body. Look through it regularly. And while you're tracking numbers, support the cells those numbers are measuring. Products like LongTails that address cellular health at the NAD+ level complement the monitoring you're doing by supporting the underlying biology.
