Threshold model of decision-making

Definitions:

1. Primary care physicians (“generalists”). Physicians specializing in Family Medicine (all ages), Internal Medicine (adults only), and Pediatrics (kids only). In Europe/UK, general practitioners (“GPs”) provide primary care to all ages. Primary care is first contact care that is comprehensive, with continuity, across a range of ages and to both sexes. Includes focus on initial evaluation of clinical problems, management of chronic disease, preventive services, and without a limit based on organ system

2. Specialists (“Partialists”). Cardiology, gastroenterology, nephrology, infectious disease, dermatology, general surgery, ophthalmology, OB/Gyn, psychiatry. Focus is on a specific part of the body.

3. Diagnosis. Classifying the cause of signs and symptoms – why are they sick? Signs: what we detect on physical exam (e.g. crackles in the lungs, heart murmur, unequal pupils). Symptoms: what patients tell us or experience (e.g. cough, headache, throat hurts).

4. Treatment. An intervention intended to provide more benefit than harm to a person with an illness or health condition (e.g. surgery, medicine, therapy).

5. Prognosis. What is going to happen to someone with disease over time (e.g. 5 year survival rate).

6. Screening. Performing tests in an asymptomatic person to detect a disease (e.g. mammography screening to detect breast cancer)

7. Chief Complaint. The patient’s primary reason for seeing the doctor, such as chest pain, cough, or refill of medications.

The Clinical Process:

Some background on how physicians work and think. A patient presents to a physician with a complaint or symptom: Key tasks -> Negotiate a management plan.

Chief complaint

1. Why are they here?

Diagnosis: Getting from a differential to a provisional diagnosis. Provisional diagnosis: what seems most likely at this point. Rule-out diagnosis: something important that has not been eliminated yet.

2. What don’t they have (ie something really bad), what might they have, and how can I narrow the possibilities?

3. Do they need any tests? In office, Ordered from elsewhere

Treatment

4. How should they be treated initially?

Prognosis

5. What can they expect?

6. Do they require follow-up? If so, when?

Example: Taking a history of a patient with bowel problems

Example: Differential diagnosis. Patient with chest pain. What would you ask?

Diagnostic strategies:

1. Pattern recognition or “Type 1 thinking”: Rapid recognition of patterns, rashes, classic symptoms or signs of disease.

2. Hypotheticodeductive or “Type 2 thinking”: Like a detective; Ask a series of questions and narrow down the diagnosis; Goal is to rule out all but one diagnosis by systematically asking a series of questions.

3. Algorithmic: order some tests, and use an algorithm to evaluate the tests.

Threshold Model

Developed by Pauker and Kassirer, 1980. To (eventually) rule-out or rule-in everything on the differential diagnosis list.

Key points to understanding the diagram:

1. Probability of disease ranges from 0% to 100%.

2. Below test threshold, disease is “ruled out” (at least for now).

3. Above the treatment threshold, we should “rule in” disease and start treatment.

4. Between thresholds, we need more information

Questions: How are thresholds determined? How do we get more information?