How does a doctor make a diagnosis?
‘Diagnosis’ means the cause of a health problem. The main role of a doctor is to decide upon the diagnosis.
To be able to make a diagnosis, doctors are trained for 4-6 years in the UK. Most of the training is learning:
- How to recognise ‘disease patterns’, via taking a history (questioning) patients and examination
- Long lists of causes of those patterns (with the most common on top)
- Analysis of risk factors and past medical and surgical problems (that helps deciding on the order of possibilities in 2).
An example of a ‘disease pattern’ is: more frequent urination (weeing) with burning, combined with being tender in the lower tummy. This is a common pattern of a urine infection.
So. Tell me more about how doctors make a diagnosis – based on a 5 step system.
1. History
Take a history (ask questions). The history is vital. Full stop.
Why? 80% of the diagnosis is in the history (10% examination, 10% tests) – so its your key diagnostic weapon.
So taking one is a doctors most important skill. The ‘past medical history’ (previous problems), and carefully going through the patient’s medications, are very important.
2. Examination
Do an examination. 10% of diagnosis comes from this. So it is important but not as important as the history. If the diagnosis can be made from the history alone, examination is not always necessary.
3. Investigation
These include blood and urine tests, and x-rays and scans. 10% of the diagnosis comes from these. These confirm the diagnosis (or rule out alternative ones). Investigations are not always necessary.
4. Diagnosis (initial or final)
If we are sure at this stage, fine .. and that is the final diagnosis. If this is not possible, we make an initial diagnosis which is the most probable at this stage, or a ‘differential diagnosis’. This phrase means a group of possible diagnoses, starting with the three most likely causes that treatment must cover – if we need to start treatment now.
If more information is needed, we wait for that, and then make the final diagnosis. If we are still not sure at this stage, we discuss with or refer to a doctor colleague. This is not usually necessary.
5. Diagnosis (final)
Note. Not all 5 are always necessary – e.g. 1 and 4 are often enough for an experienced doctor to make a diagnosis. Less experienced doctors tend to do more tests as they want to rule out more things, to feel more confident.
This leads to a ‘final diagnostic triad’:
- Syndrome. This means a recognisable pattern – e.g. back pain
- Diagnosis (final). This means the precise cause of the problem – e.g. a prolapsed (‘slipped’) spinal disc
- Pathology. This means the underlying disease process – e.g. age-related weakening of the spinal disc, leading to its expansion, so touching the spinal nerves.
An example
This is a bit different from the back pain example above.
A family reports their elderly relative is confused and may have been passing urine more frequently. The GP asks them to bring the patient in. A history confirms confusion. Examination shows they are feverish but nothing else.
The GP thinks the cause is a urine infection (initial diagnosis) but is not certain, and the patient is unwell. So time is of the essence. He/she sends the patient to hospital where a colleague (a referral) agrees with their initial diagnosis. They do blood and urine tests, and a chest x-ray (to rule out a chest cause).
After 48h of this process, the hospital team concludes that the final diagnostic triad is: ‘acute confusion’ (syndrome) secondary to ‘cystitis’ (urine infection in the bladder = final diagnosis) due to a bacterium called E Coli (pathology). The patient is given 5 days of IV antibiotics and fluids (started on admission based on initial diagnosis). The confusion clears, and they go home.
Summary
We have described how a doctor makes a diagnosis (in 5 steps). It is important to be:
- Systematic in your approach;
- Precise in your language, avoiding ‘non-diagnoses’ and jargon; and,
- Explain things clearly to patients all the way along the process – checking they understand what you say at every stage.
