The four domains, and the question each one answers
- Blood loss: acute or chronic, overt or occult — is the patient losing red cells faster than the marrow can replace them?
- Diet and exposures: iron intake, alcohol, NSAIDs, anticoagulants, chemotherapeutics — is supply inadequate or is the marrow being suppressed?
- Chronic disease and family history: inflammation, renal disease, known hemoglobinopathy — is this an anemia of inflammation or an inherited defect?
- Prior anemia episodes and prior responses to iron or B12 — is this a recurrence of a known problem or something new?
Why occult loss is the domain most often missed
A patient losing 5 to 10 mL of blood per day from a colon lesion will not notice it. Over weeks the hemoglobin falls slowly enough that the plasma volume expands to compensate, so the patient may feel only mild fatigue. The stool is not visibly black unless loss exceeds roughly 50 to 100 mL per day. This is why asking directly about stool color is unreliable and why the history must ask about change in stool caliber, rectal bleeding, and prior colonoscopy rather than relying on the patient's report of melena.
Quantifying menstrual loss
A 34-year-old woman reports "normal periods." Asked to quantify, she describes soaking through a pad or tampon every two hours on the first two days and passing clots larger than a quarter. That pattern corresponds to blood loss well above the 80 mL per cycle that defines menorrhagia, and it is enough to produce iron deficiency over time. The point of the example is not the number itself but the technique: the word "normal" from the patient and the actual volume of loss are different pieces of information, and only the second one changes the differential.
These four domains do not replace the rest of the history. They are the ones that most often change which anemia category you consider first, so they are worth asking in a fixed order every time.