Anemia Before Surgery: Why Correcting It First Changes the Outcome

A patient gets cleared for a knee replacement. The pre-op labs come back, the hemoglobin is a little low, nobody is alarmed, and the case goes forward on schedule. That sequence is extremely common and it is a missed opportunity, because between 25 and 40 percent of patients scheduled for surgery are already anemic before they ever reach the operating room, and the most common treatable cause is iron deficiency.

Anemia is one of the few surgical risk factors you can actually fix in advance. Age cannot be modified. Cardiac history cannot be modified. A hemoglobin of 11.2 can be, and the difference it makes to the recovery is not marginal. That is why we built pre-operative and surgical hematology evaluations into the practice here in White Marsh: not as a courtesy consult, but as a step that changes what happens after the incision closes.

What the Numbers Actually Show

In elective orthopedics the problem is well documented. A 2024 systematic review and meta-analysis found preoperative anemia in roughly 22 percent of patients awaiting total joint arthroplasty, with higher rates in knee replacement and in women undergoing revision procedures, and concluded that it worsens recovery while raising complication rates, transfusion rates, length of stay, readmission, and mortality.

A single-center cohort of hip and knee arthroplasty patients put hard numbers on that. Anemic patients were transfused at 34.5 percent versus 5.6 percent for non-anemic patients. Their hospital stay averaged 6.48 days against 3.36 days. ICU admission ran 47.2 percent against 29.6 percent. Those are not small differences, and the anemia driving them was present and detectable weeks before anyone reached for a scalpel.

One point of definition matters here, because it is where a lot of patients slip through. For surgery with meaningful expected blood loss, the working threshold is a hemoglobin below 13 g/dL for men and women alike. The sex-specific cutoffs many labs still flag against will clear a woman at 12.4 who is, for surgical purposes, anemic. If your pre-op protocol relies on whether the lab printed a red flag, it is missing patients.

There is a scheduling cost too, and it lands on the surgical practice rather than on us. An anemic patient discovered at the pre-op visit leaves a surgeon with three bad options: proceed and accept a higher transfusion probability, postpone a case that was already staffed and booked, or treat in the days remaining and hope the hemoglobin moves far enough.

None of those is a good use of block time. The same finding surfaced six weeks earlier is an outpatient lab draw and a treatment plan.

Low Hemoglobin Is a Finding, Not a Diagnosis

This is the part that gets compressed, and it is the part where a hematologist earns the referral. "Anemia" is not a diagnosis. It is a lab value that demands an explanation, and the explanation determines the treatment.

Iron deficiency is the most common correctable cause, but iron deficiency itself has causes. In a postmenopausal woman or any adult man, new iron deficiency anemia is an indication for gastrointestinal evaluation, because occult bleeding is on the differential until it is ruled out. Anemia of chronic inflammation looks similar on a basic panel and does not respond to iron the same way. Chronic kidney disease, B12 and folate deficiency, hemolysis, and thalassemia trait all present as a low hemoglobin and none of them are managed identically.

Handing every anemic pre-op patient a bottle of ferrous sulfate treats the number and ignores the question. Sometimes that works. Sometimes it delays a diagnosis that mattered more than the surgery.

Timing Is the Whole Game

This is the single most useful thing a surgical office can take from this post. International consensus recommends screening for anemia at least four weeks before the operation, for every patient other than those having minor procedures, specifically so there is time for treatment to work. Four to eight weeks is the practical window.

Time is what determines the treatment, not preference. With eight weeks and a cooperative gut, oral iron is reasonable. Under four weeks, or with oral iron that the patient cannot tolerate or has already failed, intravenous iron is the option that can still raise a hemoglobin before the date on the calendar. Below roughly two weeks the realistic goal shifts from correction to damage control.

So the ask for referring offices is simple, and it is not "send us more patients." It is: order the labs earlier. A CBC with a ferritin, iron studies, B12, and folate at the time surgery is scheduled, rather than at the pre-op visit, converts an unfixable problem into a fixable one. A patient identified at eight weeks has every option available. The same patient identified at eight days has almost none.

Who Should Be Screened

Not everyone needs a hematology consult. Screening is worth it for procedures with meaningful expected blood loss or a real chance of transfusion, which in practice means:

• Total joint arthroplasty, revision arthroplasty, and spine cases
• Any patient with a known history of anemia, iron deficiency, or heavy menstrual bleeding
• Patients with chronic kidney disease, inflammatory bowel disease, or heart failure, where anemia is common and multifactorial
• Patients on anticoagulants or antiplatelet agents, where bleeding risk and anemia compound each other
• Any patient who declines transfusion on religious grounds, where preoperative optimization is not optional

Referral is worth it when the cause is not obvious, when oral iron has already failed, when the timeline is tight, or when the anemia sits alongside a bleeding or clotting question that needs sorting before the operation rather than during it.

What We Do With the Referral

The workup is not complicated, and that is the point. A careful history, a targeted panel to establish the actual cause, treatment matched to the cause and to the time available, and a clear note back to the referring office with a hemoglobin trajectory the surgical team can plan around. Where a bleeding or clotting disorder is in play, that gets evaluated in the same visit rather than as a second referral.

If you have a patient scheduled for elective surgery with a hemoglobin you are not comfortable with, the useful move is to send a referral while there is still runway. The labs are cheap, the intervention is straightforward, and the alternative is finding out on the day of surgery that a fixable problem was never fixed.