The diagnostic process
Diagnosis means finding out what disease a person has. Doctors follow steps:
- History: the person describes symptoms (things they feel: pain, tiredness, thirst). The doctor also asks about past illness, family, work and habits.
- Physical examination: the doctor looks, feels, taps and listens to find signs (things others can see or measure: fever, swelling, fast pulse).
- Tests: blood, urine, scans and others to confirm or rule out.
- Thinking it through: list possible diseases (differential diagnosis) and keep the one that fits all findings best.
- Diagnosis: name the disease and its cause.
- Follow-up: check again; if the person does not improve, think again.
A symptom is felt by the patient. A sign is found by the examiner.
Disease and clinical tests
A clinical test measures something in the body to help find a disease or to follow it. The result is compared to a normal range, the band most healthy people fall in.
- Blood tests: blood count (anaemia, infection), blood sugar (diabetes), cholesterol, liver and kidney tests.
- Urine tests: sugar, protein, infection.
- Imaging: X-ray (bones, lungs), ultrasound (womb, organs), CT and MRI (detailed slices).
- ECG: electrical trace of the heart.
- Culture: grow the germ from a sample and see which medicine kills it.
- Biopsy: a tiny piece of tissue looked at under a microscope, often for cancer.
Fasting blood sugar (adult): normal about 3.9 to 5.5 mmol/L; 5.6 to 6.9 is borderline; 7.0 or more on a repeat test suggests diabetes. (In mg/dL: 70 to 99, 100 to 125, 126 or more.) A single odd result is repeated before a decision.
Main treatments
Treatment tries to cure the disease, control it, or relieve the symptoms. Five main families:
- Medicines: antibiotics kill bacteria, antivirals slow viruses, insulin lowers sugar, painkillers ease pain. Take the right dose for the full course.
- Surgery: cut, remove, repair or replace a part (appendix removal, bypass, joint replacement).
- Radiation therapy: strong rays kill cancer cells (and also chemotherapy medicines do this).
- Diet and lifestyle: less sugar and salt, exercise, stopping tobacco. For many long-term diseases this is the base of treatment.
- Rehabilitation: physiotherapy, speech therapy and exercise to get function back after illness or injury.
Others: oxygen, fluids, blood transfusion, dialysis, transplant, counselling and vaccines. Good treatment is chosen by the cause, the person, and the risks versus benefits.
Try it
Be the doctor. A friend is thirsty, tired, and runs to the toilet often. Write 3 symptoms, then name one sign you could measure (for example weight loss) and one test you would ask for. Check with step 3 of the 3D.
In the 3D: in the last step, slide the blood sugar to 4.5, 6.2 and 9.0. Which is normal, borderline and high? What would you do after each?
Key formulas and definitions
- History + Examination + Tests â Diagnosis â Treatment â Follow-up
- Symptom = felt by the patient ¡ Sign = found by the doctor
- Result inside the normal range = usual ¡ outside = clue; confirm and repeat
- Adult fasting blood sugar: normal 3.9â5.5 ¡ borderline 5.6â6.9 ¡ diabetes range âĨ 7.0 mmol/L (repeat to confirm)
- Main treatments: medicine ¡ surgery ¡ radiation ¡ diet and lifestyle ¡ rehabilitation
Worked examples
1. Which of these is a symptom and which is a sign: "I feel dizzy", "pulse 120 per minute"?
"I feel dizzy" is a symptom (felt by the patient). "Pulse 120 per minute" is a sign (measured by the examiner).
2. A fasting blood sugar is 6.2 mmol/L. What does it mean and what next?
It is above normal (5.5) but below 7.0, so borderline. The test is repeated, and diet and exercise advice is given.
3. The fasting sugar of a person is 9.2 mmol/L on two days. By how much is it above the diabetes cut-off of 7.0?
9.2 â 7.0 = 2.2 mmol/L above the cut-off. On two separate days it fits diabetes, so treatment (diet, exercise, medicine) starts.
4. Match the treatment to the case: a burst appendix, a broken leg healing, a bacterial throat infection.
Burst appendix: surgery. Broken leg healing: rehabilitation (physiotherapy). Bacterial throat infection: medicine (antibiotic).
Common mistakes
- Mixing symptom and sign. A symptom is felt by the patient; a sign is found by someone else.
- Thinking one test result is a final diagnosis. Results are clues; doctors repeat and combine them.
- Stopping an antibiotic when feeling better. Finish the course the doctor gave, or germs may come back stronger.
- Thinking medicine is the only treatment. Diet, exercise and rehabilitation are often the main treatment.