Moving Us Closer To Osler
A Miller Coulson Academy of Clinical Excellence Initiative

Knowing Your Patient


Diagnostic excellence begins and ends with knowing your patient.

A patient care story


Defining Clinical Excellence in Adult Infectious Disease Practice was published by affiliates of the Miller Coulson Academy of Clinical Excellence highlighting the following patient care story:


A 23-year-old man presented to a hospital in Turkey with 18 months of fever, weight loss, and significant cervical lymphadenopathy. The patient was born and raised in Turkey but had always lived in urban regions.


He had no pertinent animal or social exposures, and he had no significant travel history. Laboratory examination revealed a hemoglobin of 10.3 g/dL, white blood cell count of 5.2 × 109/L, erythrocyte sedimentation rate of 90 mm/h, a negative human immunodeficiency virus (HIV) test, and a normal biochemical evaluation. Blood and urine cultures were negative. A chest computed tomography scan showed right-sided paratracheal and hilar lymphadenopathy. An excisional biopsy showed necrotizing granulomatous inflammation, but it was otherwise unrevealing for infectious or malignant etiologies.


The physician was thus required to rely upon his clinical judgment to develop a treatment plan. He determined the patient’s syndrome to be most consistent with Mycobacterium tuberculosis infection based upon the patient’s history, prolonged syndrome and clinical presentation, diagnostic results (both positive and negative), and lack of epidemiologic risk for alternate etiologies. Empiric antituberculous therapy was administered, and the patient made a full recovery.



Who is your patient?

I’m an Associate Professor in the Division of Infectious Diseases at Johns Hopkins where I have the great fortune to co-direct the Microbiology/Infectious Diseases course for the first-year medical students. On the first day of class, I stress to my students that the single most important question to try and answer with every new patient encounter is: “Who is this patient?”


The answer to that question helps you build a personal rapport with the patient, understand his/her values, develop a relevant differential diagnosis, and formulate an evidence-based management approach. While most trainees grasp the concept, others—who are often highly analytical, fail to do so. For those students, I’ve attempted to translate that question into a Bayesian formula that they can relate to: “What is the pre-test probability that this patient has X?”


Knowing your patient

By knowing who your patient is, you can derive their pre-test probability for a certain disease process. Only then can you come up with a thoughtful management approach. Not a single medical diagnostic test has perfect sensitivity and specificity. As such, their positive predictive values and negative predictive values are dependent on pre-test probability. If the pretest probability is high for disease X, then a negative diagnostic test for disease X is most likely a false negative (assuming an imperfect sensitivity). When the pretest probability for disease X is low, then a positive test result is most likely a false positive (assuming an imperfect specificity). Thus, the interpretation of that diagnostic test result must include a knowledge of pre-test probability i.e. knowledge about who the patient is.


Who is this patient?

In the above patient story, our patient is an otherwise healthy 23-year-old man who lives in a TB-endemic region, who presents with a chronic history of fevers, weight loss, and lymphadenopathy. His laboratory markers suggest an acute phase response. A biopsy of a lymph node demonstrates necrotizing granulomatous inflammation. Without any further testing, we can conclude that the pre-test probability that this patient has TB is high.  Diagnostic testing, which presumably included an AFB culture of the excisional lymph node material, was negative. Culture is the most sensitive test to diagnose TB- but it is only 90% sensitive. In the setting of a high pre-test probability for TB, a negative culture result is most likely a false negative result.


By asking questions about the patient’s life, his background, his activities, in addition to his symptoms, the clinician understood who his patient was and saved his life by correctly electing to disregard the negative culture result.


A patient story from my practice

Once I was asked to see a patient by a colleague. She’d been seen for a rash that had developed around her perineum. By the time she was seen, the rash had resolved. My colleague was suspicious that the lesions represented a genital herpes outbreak so he ordered serological testing for IgG antibodies to Herpes Simplex Virus Type 1 and 2 (HSV-1 and HSV-2). The HSV-1 serologies were nonreactive but the HSV-2 serologies were reactive, and my colleague explained to the patient that the lesions were most likely an outbreak of genital herpes.


The patient was very upset. My colleague referred her to me for a second opinion. In clinic the patient was visibly upset and tearful. I felt confident that I could help her come to terms with her diagnosis. We started talking about her life, her interests, and hobbies. We found a common interest in French food and spent ten minutes talking about our favorite restaurants in Paris.


The patient then said to me, “I’ve never told anyone, but I’m a 43 year-old virgin and I just don’t understand how this could have happened”. Needless to say, not having had any sexual exposures makes her pre-test probability for having HSV-2 quite low. While not commercially available, I sent her serum for Western Blot testing to confirm the initial results. Not surprisingly, the Western Blot test was nonreactive confirming that her EIA HSV-2 result was a false positive. It was unclear what caused her perineal rash, but it was not HSV-2, and it never recurred. Had my colleague known that the patient was a virgin, he would not have ordered the HSV-2 antibodies.


Every time I walk into a patient’s room, I think to myself: “Who is this patient?” The answer to that question has allowed me to get to know these wonderful people—their joys, their fears, their aspirations, and their values, while at the same time, it has allowed me to manage them thoughtfully. As a clinician, I can’t think of a more important question to try and answer.