Does diabetes even exist? At some point these labels are more a matter of semantics than clear binary clinical determinations. For example, the current guideline is to diagnose a patient as diabetic if their uncontrolled hemoglobin A1c is over 6.5%. But the reality is that it's a spectrum with no clear dividing lines, significant fluctuations from day to day, individual genetic variations, etc.
Likewise depression is just a convenient label for a bundle of loosely correlated symptoms. Some patients are clearly having a rough time and need treatment. Because it's impractical to deal with subtle differences between patients at scale, psychiatrists have defined some subjective criteria to decide who should be treated as depressed.
The issue is that there is a measurement problem with many depression symptoms. You can have multiple people independently measure the blood glucose level of a patient and get the same result. And this result compares with other patients. With depression, you almost always have to rely on self-reporting or subjective evaluation by a health professional. One person saying they are depression might mean a whole lot more than another person saying it. It's not that you can't make measurements that are useful, its just that the error bars are so much larger.
> For example, the current guideline is to diagnose a patient as diabetic if their uncontrolled hemoglobin A1c is over 6.5%.
Several other objective tests can be used to diagnose diabetes. The disease could present with characteristic symptoms which match diabetes. The presence of comorbidities such as obesity also help with diagnosis.
> But the reality is that it's a spectrum with no clear dividing lines, significant fluctuations from day to day, individual genetic variations, etc.
This spectrum is called pre-diabetes. At some point, the risk becomes unacceptably high for the patient and treatment is indicated. This point has been determined through research.
Yes, blood glucose does vary during the day depending on the person's metabolic state. This variability is well understood. Normal and abnormal is well-defined. Fasting blood glucose > 126 mg/dl is evidence of diabetes mellitus. Blood glucose 2 hours after ingesting 75 g of glucose > 200 mg/dl is evidence of diabetes mellitus.
I'm aware of those clinical issues but I didn't want to obfuscate my original comment with a lot of irrelevant details. The point is that the decision about whether a particular disease is "real" or not is at some level a matter of semantics and arbitrary definitions. It's real because we all agree that it's real, and it seems to have some negative impact on the patient's life. And that's only partially correlated with what's actually going on inside the patient's body and mind. Quantitative blood tests are somewhat more reliable and consistent than subjective reports of psychological symptoms, but nothing is 100%. What level of certainty do we expect?
Likewise depression is just a convenient label for a bundle of loosely correlated symptoms. Some patients are clearly having a rough time and need treatment. Because it's impractical to deal with subtle differences between patients at scale, psychiatrists have defined some subjective criteria to decide who should be treated as depressed.
https://www.medscape.com/answers/286759-14692/what-are-the-d...