Stool Routine Report: Pus Cells, Occult Blood, Ova and Cysts

01

What a stool routine and microscopy actually checks

It checks the sample, not your intestine. A stool routine records how the specimen looks, then a drop is examined under a microscope for cells, parasite eggs and other material, and separate chemical tests may be added for blood. Stool analysis can identify abnormalities in faecal content such as high numbers of red cells or white cells, or the presence of parasites. That is a genuinely useful set of observations, but it is an indirect one: nothing in it visualises the gut wall.

The first honest thing to say is that most people with diarrhoea do not need it. Most patients with diarrhoea do not require laboratory evaluation, because most acute diarrhoea settles on its own with fluids and time. Stool studies earn their place when specific features are present: blood or mucus with fever, a temperature of 38.5 C or higher, severe abdominal pain, low blood volume from dehydration, age 70 or older, pregnancy, known inflammatory bowel disease, more than six stools a day, or symptoms lasting longer than a week. Those are the situations where the result can change what is done.

02

Colour, consistency, pH and mucus: which matter?

Mucus and blood matter; the rest is mostly description. Small-volume stools containing visible mucus or blood, particularly with more than about ten white cells per high-power field, are likely to originate from the large bowel and suggest an invasive bacterial cause rather than a viral one. That combination, especially alongside fever, is one of the recognised reasons to send stool studies at all. Colour and consistency are recorded for completeness and because the laboratory has to describe what it received.

Two appearances do carry weight, and neither is subtle. Black, tarry stool suggests bleeding from higher in the digestive tract and is an urgent problem rather than a laboratory curiosity. Visible red blood in someone with weight loss, anaemia or a change in bowel habit is a reason to be examined, whatever the rest of the report says. Everything else on the descriptive part of the report, including the pH line, should be read as context for the microscopy and the chemistry rather than as a finding in itself.

03

Pus cells in stool: infection, or nothing?

Pus cells are white cells, and their presence means inflammation, not a named organism. Faecal leukocytes and calprotectin are both markers of neutrophil activity and can help to distinguish inflammatory from non-inflammatory causes of diarrhoea, but they do not differentiate between infectious and non-infectious causes. So a report of pus cells in a person with fever and bloody diarrhoea supports an invasive infection, while the same finding in someone with longstanding loose stools may be pointing towards inflammatory bowel disease instead. The cells say inflammation; the context says what kind.

A small number of pus cells on their own, in someone who is well and whose symptoms are settling, usually changes nothing. This is the commonest way a stool routine causes unnecessary worry and unnecessary antibiotics. The useful questions are whether there was blood or mucus, whether there was fever, how long the symptoms have lasted, and whether the person is dehydrated. Faecal leukocytes are more likely to be associated with bacterial than with viral gastroenteritis, but they are not proof, and they are not a prescription.

04

Red cells and occult blood - piles, or something that needs looking at?

A faecal occult blood test checks for blood in a stool sample, and a positive result means it is likely there is bleeding somewhere in the digestive tract. That is all it means. It does not always mean cancer: other conditions that cause blood in the stool include ulcers, haemorrhoids, polyps and benign tumours. Visible red cells on microscopy carry the same limitation. The test detects blood; it does not locate it and it does not name the cause.

Two technical points explain most confusing results. The guaiac-based test relies on a chemical reaction that plant peroxidases from raw vegetables, red meat, povidone-iodine and even toilet sanitisers can imitate, producing false positives, while large daily doses of vitamin C can produce false negatives; the usual preparation is to avoid the interfering medicines for at least seven days and keep to a restricted diet for 48 to 72 hours before testing. Which medicines those are is for the doctor or laboratory that ordered the test to say, rather than something to work out from a leaflet, and blood thinners, including aspirin taken for the heart, are never stopped for a stool test without the advice of the doctor who prescribed them. The immunochemical test, FIT, uses an antibody to human haemoglobin, requires no dietary restrictions and detects smaller amounts of blood. It is also more specific for bleeding from the colon, because globin coming from higher up the gut is digested before it arrives, so a bleed in the stomach or duodenum can leave FIT negative. Neither test tells you where the blood came from.

Haemorrhoids are a real explanation and a dangerous assumption at the same time. They are common enough that a positive result in someone with them is easy to dismiss, and they do not protect anyone from having a second cause at the same time. Weight loss, iron deficiency anaemia, a persistent change in bowel habit, rectal bleeding or black stools, symptoms that start after the age of 50, or diarrhoea that wakes you at night are alarm features that shift the conversation from reassurance to examination.

05

Ova and cysts: which parasite, and is one sample enough?

Often one sample is not enough. An ova and parasite test looks for intestinal parasites and their eggs by examining stool under a microscope, and to get accurate results several samples may need to be collected over a few days, because parasites may not appear in the stool every day. Testing more than one sample increases the chance of finding them. A single negative report in someone with persistent symptoms is therefore weak evidence, and repeating the test properly is more useful than adding unrelated ones.

The main soil-transmitted worms are roundworm, whipworm and the hookworms, and an estimated 1.5 billion people, about 24% of the world's population, are infected. They matter beyond the gut: hookworms cause chronic intestinal blood loss that can result in anaemia, and in adolescent girls and women of reproductive age that blood loss raises the risk of maternal and infant mortality and of low birth weight. This is why a haemoglobin, ferritin and iron studies sometimes tell you more about a worm burden than the stool report does.

There is an important public health point that individual reports obscure. WHO recommends periodic deworming for at-risk groups, including preschool and school-age children, women of reproductive age and adults in high-risk occupations, without previous individual diagnosis. In other words, in many settings treatment is given on the basis of risk rather than on the basis of a stool test. A negative ova and cyst report does not override a deworming programme, and does not need to be repeated to justify one. That is a decision taken by health services for a whole group, though, and not a reason to buy deworming medicine and treat yourself, a child or someone who is pregnant on your own. Symptoms that are still going on need a diagnosis first, and the medicine should be chosen by someone who knows who is taking it.

06

Fat globules, reducing substances and undigested fibres

These lines rarely establish anything on their own. Fat in the stool is the one worth understanding, because the proper test for it is not a glance at a random sample: for detecting steatorrhoea, meaning fat malabsorption, a timed collection over 48 to 72 hours is ideal. A single report of fat globules is a hint at most, and on its own it does not establish that fat is being lost. If malabsorption is genuinely suspected, ask which test is being used to settle it rather than repeating the routine.

The tests that do change management in ongoing diarrhoea are more specific. Faecal elastase and chymotrypsin point to pancreatic insufficiency. A stool osmotic gap, calculated from stool electrolytes, separates secretory diarrhoea from osmotic diarrhoea, with a value under 50 mOsm/kg suggesting secretory and over 75 mOsm/kg suggesting osmotic. Faecal calprotectin and lactoferrin point towards inflammatory conditions such as Crohn disease or ulcerative colitis. Undigested food fibres are not on that list, and a report describing them is describing a meal rather than a disease.

07

Occult blood positive: does that always mean colonoscopy?

This is the distinction almost every report gets wrong, and it turns on one question: did you have symptoms? In a well person with no symptoms, a faecal occult blood test is a screening test. Screening is usually recommended from the age of 45 for people not at higher risk, done every year, and if the result shows blood, the most common follow-up test is a colonoscopy. In that setting, positive really does mean colonoscopy, and the point of the programme is to find things before they cause trouble.

In someone who already has symptoms, the logic runs the other way. Faecal occult blood testing is not indicated for high-risk or symptomatic patients, who should instead be referred promptly for further evaluation. A negative stool test in a person with rectal bleeding, iron deficiency anaemia, weight loss or a persistent change in bowel habit does not remove the need for that referral, because the test was never designed to answer the question being asked. A reassuring result in the wrong setting is the most expensive line on the report.

Two practical consequences follow. First, if you already have symptoms, a stool test result should never be the reason a colonoscopy is postponed. Second, in a screening context, samples should be collected from multiple areas of the stool and repeated on separate days as the kit specifies, because a single careless sample is what turns a national programme into a coin toss. Alarm features - onset after the age of 50, rectal bleeding or black stools, diarrhoea that wakes you at night, unexplained weight loss or fever, iron deficiency anaemia - all point to endoscopy regardless of the stool result.

08

When a culture or faecal calprotectin is the better test

A stool culture is the better test when the question is which organism, and the situations that justify it are well defined: blood or mucus with fever, a temperature of 38.5 C or above, severe abdominal pain, bloody stools, dehydration, age 70 or older, pregnancy, known inflammatory bowel disease, or symptoms lasting more than a week. Outside those, most acute diarrhoea is self-limited and a culture will either grow nothing or grow something that was not going to be treated anyway. Asking for one by default delays fluids, which are the treatment that matters.

Faecal calprotectin is the better test when the question is inflammation versus irritable bowel. It is a marker of neutrophil activity in the gut and points towards inflammatory diarrhoea such as Crohn disease or ulcerative colitis, which a routine microscopy cannot reliably separate from a functional disorder. It is also one of the laboratory findings that, alongside iron deficiency anaemia, a raised ESR or CRP and a positive occult blood test, makes endoscopy the right next step in someone with chronic diarrhoea. Choosing between these tests is a conversation with a doctor who has your history, not a menu to order from.