So, doing EM this month. It seems to me that in our ER, the min you see the patient, you put in all orders. We had this obese guy with subjective fevers for 3 days, non-septic, non-toxic looking. We did a full septic work up to cover our bases - never mind the guy had no findings on physical exam except symmetric weakness on finger grip test. Is it just me or are we trained wrong in the med school to go by the physical exam findings, not just subjective hx. Everything was neg and he went home on Tylenol. Patient was puzzled while his wifie, who is a nurse (was grinning and happy with all the work up we did.) Oh yeah, he is hypertensive and diabetic and we told him to go to his PCP(both have nothing to do with his "fevers"). My original plan to just do a CBC/BMP combined with his vitals would have led us to the same conclusion.
Arggh. First, I'll echo that if you have questions about the work up of a particular patient you should ask your attending or supervising resident. Second, the diagnosis of plenty of diseases are based off of subjective findings or as you may know it better - the history of present illness. Febrile seizures, TIAs, hx of rigors in ESRD patients, unstable angina, suicidal ideation, etc. While it would be nice from a medmal standpoint if we were only held to the standard of not missing diseases with obvious physical exam findings, everyone expects better us to be better than that. Based on some combination of clinical gestalt and formalized risk stratification, we decide what tests need to be ordered to rule out the worst-case scenario for whatever the patient's presenting complaint happens to be.
Obese (especially if morbid) diabetics are not renowned for their ability to effectively clear bacterial infections and depending on the level of obesity, the diagnostic value of the physical exam will be degraded by body habitus. If the patient isn't sick, it doesn't really matter what work-up you do (including not doing any) so in a very real way you don't get points for suggesting a more minimalistic work-up for this patient. The problem arises in the patient that could be sick. Your initial work-up features a test with relatively poor AUC for most diseases (assuming you're looking for WBC count on the CBC) and a reasonable screen for significant electrolyte abnormalities (although with B hand weakness you could considering adding on a phosphorous). Since you're not giving me an indication that the patient/wife had a hidden agenda in coming to the ED (work-note, avoiding incarceration, drug-seeking, etc.), I'd want to know what the guy (or more likely his wife) was worried about. Playing the odds right now it's a viral illness, but with B hand weakness and reported fever it could be something as dangerous as early cord compression from an epidural abscess. I'm not saying the guy needed an MRI, but it's possible your attending went hunting to find a more benign cause for the patient's symptoms while buying time to observe the guy for progression of symptoms.
In terms of ordering everything in one go, it's actually relatively uncommon in medicine to systematically hunt down diseases in a serial fashion. Most medicine specialties will have some version of a shotgun work-up that they order initially (GI chasing elevated LFTs, heme/onc working up anemia, rheumatology going after an autoimmune disease, etc .) even in the face of convincing evidence for a particular cause of the disease. A lot of intern year is spent figuring out what to load the shotgun with depending on the service you're rotating through. In the ED, ordering multiple rounds of tests sometimes is necessary because of changing patient conditions or new history (family arrives and says grandma's face was drooping for 30 min). In general though, most of our testing pattern in based off of the fact that many of our patients' pre-test probability of disease is in an intermediate zone and that unremarkable basic labs may not be sufficiently sensitive to drop the post-test probability low enough to rule out the disease.