Cat Iron Panel: 60-200 ug/dL, 3 Ferritin Tiers, 2 Splits

A cat iron panel is three numbers pretending to be one. Serum iron in a healthy adult cat usually reads 60 to 200 µg/dL, ferritin says how much is actually stored, and the reticulocyte count says whether the marrow is answering. Read any one alone and it can point the wrong way; the usual bill is a cat treated for deficiency that really has inflammation.

Two thresholds organise everything below. Transferrin saturation under 15 percent with a total iron binding capacity above 350 µg/dL is the deficiency pattern. Saturation between 15 and 25 percent with TIBC under 250 µg/dL is the inflammation pattern. The two look identical on serum iron and are treated in opposite directions.

The 60-200 µg/dL band measures transport, not storage

Serum iron counts iron currently loaded onto transferrin, the carrier protein. It is a snapshot of a queue, not a warehouse. Unit conversion trips people up: 1 µg/dL equals 0.179 µmol/L, so 60 µg/dL is 10.7 µmol/L and 200 µg/dL is 35.8 µmol/L. A US lab printing 90 µg/dL and a European lab printing 16 µmol/L are describing the same cat on the same morning.

Two sampling facts move the value more than most disease does. Serum iron peaks in the morning and can fall 10 to 20 percent by late afternoon, so draw at a fixed hour, ideally between 08:00 and 10:00. Hemolysis of even 1 percent of the red cells releases hemoglobin iron and pushes the reading up by 10 to 30 percent; a lipemic sample after a fatty meal adds 5 to 15 percent. Fast 8 to 12 hours, separate serum within 2 hours, and never use an EDTA tube: the chelator strips iron and reads 20 to 40 percent low.

Ferritin comes in three tiers, and the middle one is the trap

Ferritin is the storage protein and the closest thing to a bank statement. Feline intervals differ by supplier and antibody, commonly landing between 20 and 100 ng/mL, so the only interval that applies is the one printed on your own report.

Tier 1 sits below the lower limit, often under 20 to 30 ng/mL. Stores are empty, and this is the one tier that supports iron deficiency on its own.

Tier 2 sits inside the interval but in the bottom third, roughly 30 to 60 ng/mL. Ferritin is an acute phase reactant and climbs within 24 to 48 hours of inflammation, so a genuinely depleted cat with a dental abscess or dermatitis can land in the middle of the reference band and look fine.

Tier 3 sits above the upper limit, over roughly 100 ng/mL. Stores are present. When serum iron is low and ferritin is high, the diagnosis is anemia of inflammation and oral iron will not fix it.

Two differentiations that decide the next step

The first is regenerative versus non-regenerative. Ask for an absolute reticulocyte count, not a percentage; percentages move with the red cell count. Under 60,000/µL is non-regenerative. Above that, the marrow is responding and chronic blood loss leads the list: fleas, hookworms, a bleeding mass, a clotting defect. Response takes 3 to 5 days, so a sample drawn on day 1 of bleeding looks non-regenerative and proves nothing.

The second is iron deficiency versus anemia of chronic disease, and transferrin saturation separates them. Calculate it as serum iron divided by TIBC, times 100. Under 15 percent with TIBC above 350 µg/dL means the body is building more carrier because it wants iron. Inflammation does the reverse: TIBC drops under 250 µg/dL, saturation sits between 15 and 25 percent, and ferritin rises. A cat in that second pattern given iron tablets shows no response in 14 days.

Reference intervals worth carrying to the clinic

Test	Typical feline interval	Unit	Decisive cut-off
Serum iron	60-200	µg/dL	under 60 with low ferritin
Total iron binding capacity	250-400	µg/dL	over 350 in deficiency, under 250 in inflammation
Transferrin saturation	25-45	percent	under 15 deficiency, 15-25 inflammation
Ferritin	20-100	ng/mL	under 20 empty, over 100 inflammation
Absolute reticulocytes	under 60,000	per µL	over 60,000 means regeneration
Packed cell volume	30-45	percent	under 20 needs same-day care
Hemoglobin	9-11	g/dL	under 7 is severe

Intervals are population tools, not individual truths: a 12-year-old cat with creatinine 2.1 mg/dL and packed cell volume 32 percent is anaemic for itself even though 32 sits inside the printed range.

Age, hydration and instrument: three modifiers

Age shifts the whole panel. Kittens under 12 weeks run packed cell volumes around 25 to 35 percent, below the 30 to 45 percent adult band, and most iron intervals come from adult reference populations, which makes a normal kitten look abnormal on an adult form. Cats over 10 years carry a higher chance of chronic kidney disease and hyperthyroidism, and both change hydration and protein status before they change iron.

Hydration is the fastest modifier. At 5 percent dehydration, serum iron, TIBC and ferritin concentrate by roughly 5 to 8 percent; at 8 percent the same sample reads 10 to 15 percent high. Recheck 24 hours after fluid therapy before believing an isolated high value, and compare the panel against measured intake, using the arithmetic in cat water metabolism.

Then the instrument. A benchtop analyzer and a point-of-care cartridge can disagree by 10 to 20 percent on one sample, and two labs using different ferritin antibodies can disagree by more. Different laboratories vary slightly, so trend at least 3 consecutive samples on one analyzer and record which machine produced each number.

When the panel stops being a puzzle

White gums, a packed cell volume under 20 percent, hemoglobin under 7 g/dL, a sleeping heart rate over 200 beats per minute, or breathing over 40 breaths per minute at rest all mean the cat is compensating badly. So does a packed cell volume falling 3 points in a week. Those are same-day visits with bloodwork and imaging, not a supplement trial at home.

Five steps for the next blood draw

Fast 8 to 12 hours, draw between 08:00 and 10:00 into a serum tube, and collect 3 mL, enough for iron, TIBC and ferritin in one run.
Order serum iron, TIBC, ferritin, absolute reticulocytes and a packed cell volume together; 5 numbers from one draw cost less than 2 rounds of guessing.
Compute saturation yourself: iron divided by TIBC times 100. Under 15 percent with TIBC over 350 µg/dL points to deficiency, 15 to 25 with TIBC under 250 points to inflammation.
Repeat in 7 to 14 days on the same analyzer before changing diet or litter routine.
Do not start iron by mouth on a ferritin result alone, and never give human iron tablets to a cat; the gap between therapeutic and toxic is narrow and the decision belongs to a veterinarian. For breed background, the breed quiz is a faster start.

Frequently asked

My cat's serum iron is 55 µg/dL. Is that iron deficiency?

Not on its own. At 55 µg/dL you are just under the 60 µg/dL floor, which is a transport number that drops 10 to 20 percent across a single day. Ask for ferritin and TIBC on the same serum sample: a ferritin under 20 ng/mL with TIBC over 350 µg/dL supports deficiency, while a ferritin over 100 ng/mL with TIBC under 250 µg/dL points to inflammation. Repeat both in 7 to 14 days on the same analyzer before treating.

Why can a cat with empty iron stores have a normal ferritin?

Because ferritin is an acute phase protein. Any inflammation, including dental disease, dermatitis or a tumor, raises it within 24 to 48 hours, lifting a depleted cat from 15 ng/mL into the 40 to 60 ng/mL middle of the interval. That is the grey tier, and it is why a single ferritin is read next to serum iron, TIBC and the absolute reticulocyte count rather than alone. Saturation under 15 percent with TIBC over 350 µg/dL is the combination that survives the noise.

Can I just give an iron supplement and recheck in a month?

No. Iron given to a cat with anemia of inflammation produces no rise in 14 days and adds gastrointestinal risk, and human iron tablets are a common poisoning in small animals. The safe sequence is a fasted morning draw, all 5 numbers from one tube, a calculated saturation, and a repeat in 7 to 14 days on the same analyzer. If the packed cell volume is under 20 percent or hemoglobin under 7 g/dL, skip the trial and see a veterinarian the same day.