Black, tarry stool that sticks to the tray and smells of iron is digested blood, which means the bleeding started 8 to 24 hours earlier somewhere above the colon. Treat the first black stool as a 6-hour problem: call, then be at the clinic within 6 hours. If the cat is pale, weak, vomiting blood, or passing black-red jelly, the line is 60 minutes; if it has collapsed, it is 0 minutes and you carry it to the car.
Melena is common and rarely dramatic at the start, which is the trap. A cat can lose 15 percent of its blood volume into the gut and still jump on the counter, so the stool, the gum colour and the heart rate are the 3 readings that matter, not how the cat behaves.
3 checks that separate melena from dark food
Melena is black, glossy and sticky, leaves a tarry ring on the tray, and the smell is hard to mistake for anything else. Three checks settle it in 10 minutes. Recall the last 48 hours of food for blood meal, liver, charcoal treats or iron tablets. Smear a pea-sized sample on white paper: melena bleeds a red-brown halo into the paper, food does not. Photograph the stool beside a coin and bag 5 to 10 g in a sealed container for the vet, because the sample is worth more than a description.
The 6-hour line and its 4 exceptions
| Finding | Blood loss (mL) | Black stools | Act within |
|---|---|---|---|
| 1 black stool, cat bright | 50-100 | 1 | 6 h |
| 2-3 black stools, pale gums | 150-250 | 2-3 | 60 min |
| Vomiting blood plus melena | 200-400 | 2+ | 0 min |
| Black-red jelly, collapse | 300+ | 3+ | 0 min |
| Dark stool, normal cat, food recall | 0 | 1 | 48 h |
A 4 kg cat holds about 280 mL of blood, so 150 mL is more than half the circulating volume, and a 15 percent loss drops the hematocrit by roughly 10 points. That arithmetic is why 2 black stools with pale gums is a 60-minute number while 1 black stool in a bright cat is a 6-hour number.
3 cause classes, in the order a vet checks them
The split matters because the first class is treated with acid suppression, the second by finding the source, and the third with clotting support or an antidote. Getting the class wrong sends a bleeding cat home with the wrong drug, and a rodenticide case that waits 24 hours can bleed for another 72.
Class 1: ulceration in the upper tract
Most cases in cats over 8 trace to the stomach or duodenum. The usual history is an anti-inflammatory painkiller given for 3 or more days, or a steroid course lasting 2 or more weeks, or chronic kidney disease with urea above 60 mg/dL. Ulcers bleed slowly, 5 to 20 mL a day, which turns stool black without changing the cat's energy for 3 to 5 days.
Class 2: swallowed blood
Blood from the nose, mouth or lungs is swallowed and comes out black 8 to 24 hours later. Look for a 2 to 5 mm nick on the tongue, a bleeding tooth socket 1 to 3 days after an extraction, or a sneeze with blood in it. This class resolves once the source stops, which is why the mouth exam comes before any endoscope is booked.
Class 3: clotting failure
Anticoagulant rodenticide, liver failure and a platelet count under 50,000 all present as melena plus bruising or petechiae elsewhere. Rodenticide shows up 3 to 7 days after ingestion and can bleed for 24 to 72 hours before the stool changes at all. If bait exposure is even possible, say it in the first sentence at the desk: treatment is a 4 to 6 week course and it starts before the lab result returns. The toxin checker lists the baits that cause this pattern.
What not to do before the cat is seen
- No human painkiller at any dose: 1 adult 200 mg tablet can be 10 to 20 times a cat's safe exposure.
- No hydrogen peroxide and no salt water to induce vomiting; both cause the gastritis you are trying to stop.
- No iron supplement and no activated charcoal at home. Iron blackens stool and hides the trend; charcoal binds the drugs the vet will give.
- Do not fast the cat past 12 hours without instruction. Fat mobilization starts within 48 to 72 hours, and hepatic lipidosis is worse than the bleed.
- Do not clean the tray before you photograph it, and do not bin the sample.
What the first hour at the clinic should include
A PCV and total protein, repeated at 4 hours, because a cat can bleed into the gut and hold a normal PCV for 6 to 12 hours before dilution shows. A platelet count and a coagulation panel if there is bruising anywhere. A bedside ultrasound for free fluid and gut wall thickness. An oral exam under good light. Endoscopy is usually booked at 24 to 48 hours, once the cat is stable enough for anesthesia, not on arrival.
The 48-hour and 7-day checks
Stool turns from black to dark brown 24 to 72 hours after bleeding stops, so a black stool at 72 hours means the bleed is still running. Weigh the cat on days 1, 3 and 7, and recheck PCV at 24 and 72 hours. A cat that eats on day 2 but drops 200 g by day 7 needs the ulcer workup repeated, not a stronger antacid. Aftercare for a cat that came home with a catheter or a drip follows the same 48-hour logic as the post-catheter routine: count, weigh, photograph, then call.
5 steps today
- Photograph the stool beside a coin and bag 10 g of it in a sealed container.
- Write down every drug given in the last 14 days, including supplements, flea products and any bait in the building.
- Press the gums and time the refill: under 2 seconds is reassuring, over 2 seconds means go now.
- Call the clinic and say the words black tarry stool, not stomach upset.
- Ask whether the cat may eat on the way in; most are allowed a small meal, and fasting is the vet's call.
Terms mentioned in this article
Frequently asked
Is one black stool an emergency?
It is a 6-hour problem, not a 6-day one. One black stool in a cat with pink gums, a normal resting rate and normal behaviour can wait until the clinic opens, as long as that is inside 6 hours. Two black stools, pale gums, vomiting blood or any collapse moves it to 60 minutes or 0 minutes.
Can food make stool look like melena?
Yes, and 3 foods do it most often: blood meal in raw diets, cooked liver, and charcoal or iron supplements. The paper test separates them: melena bleeds a red-brown halo into white paper, food does not. Stop the suspect food for 48 hours and the stool should lighten within 1 to 2 days if food was the cause.
How much blood does a cat have to lose to pass black stool?
About 50 mL, which is under 20 percent of the 280 mL a 4 kg cat carries. That is why melena is a late sign of a slow bleed rather than an early sign of a big one, and why the gum colour and the heart rate are checked at the same time as the stool.