How to check your symptoms, step by step

Why online symptom quizzes often get it wrong

Automated symptom checkers ask a few yes-or-no questions and return a list of possible conditions. Independent studies have found they often miss the correct diagnosis and tend to be overcautious with triage. They cannot examine you, they cannot tell how unwell you look, and they do not know your history.

A better approach is to do what a clinician does: gather the right details, check for danger signs, and then read about the causes that fit. You stay in control of the reasoning, and you arrive at an appointment with facts rather than a guess.

Step 1: Rule out red flags

Before reading about causes, check whether any warning sign applies. These point to problems that need care the same day or an emergency room:

• Sudden, severe pain anywhere, especially if it is the worst you have had
• Chest pain, pressure or tightness, particularly with breathlessness, sweating or nausea
• Shortness of breath at rest, or blue lips
• New confusion, slurred speech, or one-sided weakness or numbness
• Fever with a stiff neck, a rash that does not fade when pressed, or drowsiness
• Any fever in a baby under 3 months of 38 °C (100.4 °F) or higher
• Vomiting blood, black stools, or heavy rectal bleeding
• Severe abdominal pain with a hard belly, or pain with fainting
• Thoughts of harming yourself (call or text 988 in the US)

A few "slow" red flags do not need the ER but should not be ignored. Book a doctor's visit within a week or two for:

• Unexplained weight loss (more than 5% of your body weight over 6 to 12 months without trying)
• Night sweats that soak your sheets
• A new lump, or swollen lymph nodes lasting more than 2 to 3 weeks
• A cough lasting more than 3 weeks, or any coughing up of blood
• Blood in the urine or stool
• Difficulty swallowing that is getting worse
• A change in bowel habit lasting more than a few weeks, especially after age 45
• Bleeding after menopause

Step 2: Describe the symptom precisely

Doctors use a checklist to pin down any symptom. Working through it yourself narrows the possible causes more than anything else. A useful memory aid is OLD CARTS.

Then add the context:

• Other symptoms that came with it: fever, nausea, rash, weight change, urinary or bowel changes, cough, dizziness
• Triggers or events: a new medicine, travel, an injury, a new food, sick contacts, a tick bite, a new sexual partner
• Your background: age, long-term conditions, pregnancy or chance of pregnancy, smoking, alcohol, family history
• Medicines you take, including over-the-counter drugs, supplements and herbal remedies

Why the details matter

Small differences change the likely cause a lot. Take headache: a slowly building headache with a tight band around the head suggests a tension headache, while one-sided throbbing with nausea and light sensitivity suggests migraine. A headache that hits full strength within a minute is an emergency. Side pain that comes in waves and spreads to the groin points toward a kidney stone, while steady side pain with fever and burning urine suggests a kidney infection.

Step 3: Read about causes that fit

Start with the guide for your main symptom. Each iSymptom symptom page lists common causes first, then serious ones, with the clues that separate them. While reading:

• Think common first. Common conditions with unusual features are more likely than rare diseases with typical ones.
• Match the pattern, not one word. A cause should fit your onset, location, timing and other symptoms, not just share one feature.
• Note what would change your plan. Each guide has a triage box listing signs that make a visit urgent. Watch for those.
• Use reliable sources. Good sources name their references, show when they were updated, do not sell treatments, and agree with sites such as MedlinePlus, the CDC, the NHS and specialty medical societies.
• Look up unfamiliar words in the medical glossary.

Avoid jumping to the worst possibility. Reading about rare cancers when you have a two-day cough causes worry without adding useful information.

Step 4: Keep a symptom diary

A diary turns a vague memory ("it's been bad on and off") into evidence a doctor can use. It is especially helpful for symptoms that come and go, such as headaches, dizziness, palpitations, bowel problems, fatigue or pain that flares.

Copy this template into a notebook or notes app and fill in one row per episode or per day:

Also track, when relevant:

• Temperature readings, with the time and method (mouth, ear, forehead)
• Blood pressure or blood sugar readings if you have a home monitor
• Menstrual cycle days
• Sleep hours, caffeine and alcohol
• Photos of rashes, swelling or color changes, dated, since these can fade before your appointment

Two to four weeks of entries are usually enough to show a pattern.

Step 5: Decide where to go

For a fuller comparison, see ER, urgent care or primary care.

What to bring to your appointment

• Your OLD CARTS summary, written down in a few lines
• Your symptom diary and any photos
• A list of all medicines, doses and supplements, or the bottles themselves
• Your allergies and past reactions to medicines
• Past medical history: surgeries, long-term conditions, recent tests and results
• Family history of relevant conditions, such as heart disease, cancers or diabetes
• Your top 2 or 3 questions, with the most important first

Useful questions to ask:

• What do you think is most likely, and what else are you considering?
• Do I need tests, and what will they tell us?
• What should I do if it gets worse, and which signs mean I should come back sooner or go to the ER?
• How long until it should improve?

At the end, repeat the plan back in your own words. If something was unclear, ask before you leave.

Start with a symptom guide

Browse every guide in symptoms A to Z, or search the site.