A cat blood panel is read in 4 passes: find the 6 values that carry most of the story, compare each with the reference interval printed on that same sheet, check the 2 kinds of marker the analyzer adds, then run 4 verification checks before you draw any conclusion. One value outside the interval is not a diagnosis; 3 values moving in the same direction across 2 tests 4 weeks apart is a pattern worth a conversation.
Reference intervals belong to the lab, not the internet
Every analyzer builds its own intervals from its own population, and the same creatinine can read normal at 1 laboratory and high at another. A cat creatinine of 200 umol/L sits inside a 71 to 212 interval on one sheet and above a 60 to 180 interval on another. Always use the numbers printed in the right-hand column of the report in front of you, and if the sheet has no intervals at all, ask for a version that does. Printed intervals usually carry the sample size behind them, often 100 to 300 healthy cats, which tells you how much room the range allows.
The 6 values to find first
Scan the page for these 6 before reading anything else. They cover kidney function, liver leakage, blood sugar, potassium, and red cell volume, which is the fastest route to knowing whether the problem is urgent.
| Value | Typical feline interval | Unit | Separated within | Common interference |
|---|---|---|---|---|
| BUN | 5.4 to 13.6 | mmol/L | 4 h | high protein meal, dehydration |
| Creatinine | 71 to 212 | umol/L | 4 h | muscle mass, ketones |
| ALT | 10 to 100 | U/L | 8 h | hemolysis, storage at room temperature |
| Glucose | 3.9 to 8.3 | mmol/L | 2 h | stress, delayed separation |
| Potassium | 3.5 to 5.8 | mmol/L | 4 h | hemolysis raises it falsely |
| HCT | 30 to 45 | percent | 6 h | dehydration, fluid therapy |
Marker type 1: the H and L flags
The analyzer prints an H or an L beside any result outside its interval, and a single H is not a verdict. Roughly 1 in 20 results from a healthy cat falls outside the interval by chance alone, so a panel of 20 tests will show about 1 flag on a well cat. Read the flag as a pointer: it tells you which line to compare with the previous report, not which disease the cat has. Two flags in the same organ group, for example BUN and creatinine together, carry more weight than 2 flags in unrelated groups.
Marker type 2: the review and sample marks
The second set of marks belongs to the laboratory, not the machine. An asterisk or a small triangle usually means a technologist looked at the result by hand, a double asterisk often flags a value confirmed on a repeat run, and a letter in the comment column codes the sample itself: H for hemolysis, L for lipemia, I for icterus. A hemolyzed sample can push potassium up by 0.5 to 1.5 mmol/L and ALT up by 20 to 50 U/L with no disease at all, which is why a potassium of 6.0 mmol/L on a hemolyzed tube gets repeated before anyone treats it.
The 4 verification checks, in order
- Name, patient ID, and 2 dates: the draw date and the report date. A gap over 24 hours at room temperature changes glucose and potassium.
- Units and conversion. Creatinine in mg/dL multiplies by 88.4 to give umol/L; glucose in mg/dL multiplies by 0.0555 to give mmol/L. A report mixing the 2 systems is a common source of panic.
- Reference intervals that match this laboratory and this analyzer, not a range copied from a website or an older report.
- Sample quality marks: hemolysis, lipemia, icterus, and any note about a short sample or a clotted tube.
Why 1 abnormal value is usually not a diagnosis
Veterinary panels are read against the cat, not against the sheet. A glucose of 9.5 mmol/L in a cat that fought the carrier for 3 minutes is stress hyperglycemia in most cases; the same number in a quiet cat that drinks 400 ml a day means something else. ALT can rise 3 to 5 times above the top of the interval after 1 sedative event and fall back within 14 to 21 days. The useful question is not whether the value is outside the line, but how far outside and whether it moved.
Distance matters as much as direction. A creatinine 10 percent above the top is a recheck in 4 weeks; 3 times the top is a same-week conversation about fluids, blood pressure, and urine concentration.
Read the trend, not the snapshot
Keep every report in 1 folder with the draw date on the file name. Two panels 4 weeks apart answer questions a single panel cannot: a creatinine rising from 180 to 240 umol/L over 30 days is a different signal from a stable 240 for 12 months. Cats lose 3 to 5 percent of kidney function a year in normal aging, and a creatinine that climbs 20 percent in 6 months is worth a urine protein check. A weight trend chart kept beside the lab folder adds the other half: a 300 g drop across 2 panels usually explains a rising BUN better than any single result.
When the numbers mean now, not next month
- Potassium above 6.5 mmol/L, or below 2.5 mmol/L, with weakness or a slow heart rate.
- Glucose above 20 mmol/L with vomiting, or below 3.0 mmol/L with wobbling or a seizure.
- HCT below 15 percent, or a PCV that dropped 5 points in 24 hours.
- Creatinine above 440 umol/L with no urine produced for 12 hours.
These 4 are not reading exercises. Call the clinic, describe the number, and say when the sample was drawn.
Three sentences to say at the desk
Ask which values the vet is treating and which are being watched, ask whether the interval on the sheet belongs to this laboratory, and ask what number at the next recheck would change the plan. A clinic that answers all 3 in plain words gives you a usable file; if any answer is a single word, ask for it in writing on the discharge note. If the cat may have eaten a plant or a human medicine, run the name through the toxic plant and product list before the next visit and take the list entry with you, because a named substance changes which values get rechecked.
A 6-line summary you can write yourself
Fill this in after every panel: draw date, the 1 value furthest outside its interval, the 1 value that moved most since last time, any sample quality mark, the recheck date, and 1 question for the vet. Six lines take 5 minutes and make the next appointment 10 minutes shorter.
Terms mentioned in this article
Frequently asked
Why does my cat's creatinine read high at one lab and normal at another?
Each analyzer sets its own intervals from its own reference population, so a creatinine of 200 umol/L can sit inside a 71 to 212 range and above a 60 to 180 range. Use the interval printed on the sheet in front of you, never one copied from a website or an old report.
What do the H and L flags on a cat blood panel mean?
They mark a result outside the analyzer's interval, nothing more. About 1 in 20 results from a healthy cat falls outside by chance, so a 20-test panel will usually show 1 flag. Two flags in the same organ group matter more than two unrelated ones.
Which lab values mean I should call the clinic today?
Potassium above 6.5 or below 2.5 mmol/L, glucose above 20 or below 3.0 mmol/L, HCT below 15 percent, or creatinine above 440 umol/L with no urine for 12 hours. Report the number and the draw time when you call.