Anemia Penyakit Kronis

01Pathophysiology

The central player in anemia of chronic disease is hepcidin, a peptide hormone produced by hepatocytes. In any state of chronic inflammation, pro-inflammatory cytokines, particularly interleukin-6 (IL-6), stimulate the liver to produce hepcidin in large quantities. Understanding what hepcidin does to iron metabolism is the key to understanding every lab finding in this disease.

Hepcidin acts by binding to and degrading ferroportin, the only known cellular iron export channel. Ferroportin sits on the surface of two critical cell types: duodenal enterocytes (which absorb dietary iron) and macrophages (which recycle iron from senescent red blood cells). When hepcidin destroys ferroportin on enterocytes, dietary iron absorption drops. When it destroys ferroportin on macrophages, recycled iron gets trapped inside macrophages and cannot be released into the plasma for use by the bone marrow. The result is a state of functional iron deficiency: total body iron stores are normal or even elevated, but the iron is sequestered and unavailable for hemoglobin synthesis.

Additionally, chronic inflammation directly suppresses erythropoiesis through several mechanisms. TNF-alpha and interferon-gamma inhibit erythroid progenitor proliferation in the bone marrow. There is also a blunted erythropoietin (EPO) response: the kidneys produce EPO in response to anemia, but the levels achieved are inappropriately low relative to the degree of anemia. This is because inflammatory cytokines reduce renal EPO gene expression. Furthermore, inflammatory cytokines shorten red blood cell survival from the normal ~120 days to approximately 80 to 90 days.

The combination of iron sequestration, suppressed marrow activity, blunted EPO response, and shortened RBC lifespan produces a mild-to-moderate anemia that is typically normocytic and normochromic. However, in longstanding or severe cases (especially when coexisting with conditions like rheumatoid arthritis), the anemia can become microcytic and hypochromic because the degree of iron restriction to erythroblasts eventually impairs hemoglobin synthesis at the cellular level, mimicking iron deficiency anemia on the CBC.

02Classification and Clinical Manifestation

Anemia of chronic disease does not have a formal staging system in the way that cancers do, but it is clinically useful to categorize its presentation based on severity and MCV behavior, as this directly affects the diagnostic reasoning on exam vignettes.

By Underlying Disease Category

03Diagnostic Workup

The workup begins when a CBC reveals anemia (hemoglobin below 13 g/dL in men, below 12 g/dL in non-pregnant women) in a patient with a known chronic disease. The MCV will usually be normal (80 to 100 fL), which places this in the normocytic anemia category.

The best initial diagnostic step is to order iron studies: serum iron, TIBC, transferrin saturation, and serum ferritin. This panel is the single most important set of tests on the exam because it distinguishes ACD from its closest mimic, iron deficiency anemia. The hallmark pattern is low serum iron with low TIBC and elevated ferritin. The logic: in ACD, the body has plenty of iron (hence the high ferritin, which reflects total body stores), but it is being hoarded by macrophages and not released into the bloodstream (hence the low serum iron). The TIBC is low because the liver downregulates transferrin production during inflammation; it has no need to increase iron-carrying capacity when the body "believes" there is enough iron.

This is the opposite of iron deficiency anemia, where the body is genuinely depleted of iron. In IDA, the liver ramps up transferrin production (high TIBC) in a desperate attempt to capture whatever little iron is circulating, while ferritin drops because stores are truly empty.

When the vignette presents a mixed picture (e.g., a patient with rheumatoid arthritis who also has menorrhagia), the ferritin may be in a "gray zone" of 30 to 100 ng/mL, falsely elevated by inflammation despite true concurrent iron deficiency. In this scenario, the soluble transferrin receptor (sTfR) becomes the critical test. sTfR is elevated when marrow erythroblasts are genuinely iron-starved and is not affected by inflammation, unlike ferritin. The sTfR/log ferritin ratio is the most accurate lab test for distinguishing pure ACD (<1) from ACD with concurrent true iron deficiency (>2).

A bone marrow biopsy with Prussian blue iron stain is the most accurate overall test (gold standard). It will show increased stainable iron in macrophages (proving iron is present in the body) but decreased sideroblasts (proving iron is not being delivered to developing red cells). However, this is invasive and rarely performed in clinical practice solely to diagnose ACD. On the exam, it appears as an answer choice when the question asks for the "most accurate" or "confirmatory" test.

Reticulocyte count will be inappropriately low, confirming that the bone marrow is not mounting an adequate response. If the reticulocyte count is elevated, consider hemolysis or acute blood loss rather than ACD.

04Management and Treatment

Step 1: Identify and treat the underlying disease. This is always the most important and most testable answer. A vignette describing a patient with newly diagnosed ACD whose underlying condition has not been addressed will have "treat the underlying condition" as the correct next step. For example, if a patient with untreated rheumatoid arthritis presents with normocytic anemia, low iron, low TIBC, and high ferritin, the answer is to initiate disease-modifying therapy for RA, not to start iron or EPO.

Step 2: Assess for concurrent true iron deficiency. Before dismissing the anemia as "just ACD," rule out coexisting IDA. If transferrin saturation is below 20% and ferritin is below 100 ng/mL in the context of inflammation, there may be a true iron deficit on top of ACD. In these patients, IV iron is indicated. Oral iron (ferrous sulfate 325 mg, containing 65 mg elemental iron, taken 2 to 3 times daily) is generally ineffective because hepcidin blocks ferroportin on enterocytes, preventing absorption. IV iron preparations (iron sucrose, ferric carboxymaltose, ferumoxytol) bypass this blockade entirely and deliver iron directly to the bloodstream.

Step 3: Consider ESAs. Erythropoiesis-stimulating agents are indicated in two primary populations: CKD patients and cancer patients receiving myelosuppressive chemotherapy. In CKD, the anemia is driven partly by EPO deficiency, making ESAs particularly effective. The target hemoglobin is 10 to 11.5 g/dL. Overshooting to hemoglobin above 13 g/dL has been shown in clinical trials (CHOIR, CREATE, TREAT) to increase the risk of stroke, myocardial infarction, heart failure, and death. In cancer patients, ESAs should only be used when the goal of chemotherapy is palliative, not curative, because ESAs may promote tumor growth via EPO receptor signaling on tumor cells.

Step 4: Transfuse only for severe, symptomatic anemia. The threshold is generally hemoglobin below 7 g/dL, or higher in patients with active cardiovascular disease (threshold of 8 g/dL). Transfusion provides immediate symptomatic relief but does nothing to address the underlying mechanism.

Contraindications and cautions:

• ESAs are contraindicated in uncontrolled hypertension (they can worsen it) and in patients with a history of pure red cell aplasia from prior ESA use (anti-EPO antibodies).

• ESAs carry a black box warning for increased mortality and tumor progression in cancer patients when targeting hemoglobin above 12 g/dL.

• Oral iron is not the answer in pure ACD. This is one of the most commonly tested traps. The question stem will describe classic ACD iron studies, and oral iron supplementation will be a tempting but incorrect answer choice.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common way students lose points on anemia of chronic disease questions is by confusing the iron study pattern with iron deficiency anemia. Both conditions present with low serum iron, and if the student stops reading the labs at "low serum iron" and picks iron deficiency, they will get the question wrong. The exam is testing whether you can interpret the full iron panel as a unit. The reflex must be: low serum iron prompts you to look at TIBC and ferritin immediately. Low TIBC + high ferritin = ACD. High TIBC + low ferritin = IDA. This pattern recognition is non-negotiable.

The second major trap involves management. Once you diagnose ACD, a tempting answer choice will be "start oral iron supplementation." This is wrong for pure ACD because the problem is not iron deficiency but iron sequestration, and oral iron will not be absorbed effectively due to hepcidin blocking ferroportin on enterocytes. The correct answer is almost always to treat the underlying disease. IV iron is only appropriate when concurrent true iron deficiency has been documented.

A third trap appears in the microcytic variant of ACD. A longstanding case of ACD (e.g., a patient with RA for 10 years) may present with an MCV below 80 fL, which makes the student default to IDA. But the iron studies will still show the ACD pattern. The exam is testing whether you anchor to the MCV or to the iron studies. Always anchor to the iron studies.

Finally, students must remember the ferritin gray zone problem. In a patient with both chronic inflammation and a possible additional source of iron loss (GI bleeding, menorrhagia), ferritin can sit in the 30 to 100 ng/mL range. This is "normal" on paper but may be falsely elevated by inflammation and actually represents depleted stores. When you see a ferritin in this range alongside an inflammatory condition and clinical suspicion for bleeding, the correct next step is to order the soluble transferrin receptor or the sTfR/log ferritin ratio to unmask the hidden iron deficiency. This is a high-level question that distinguishes top-scoring students from the rest.

The core competency being tested across all anemia of chronic disease questions is the ability to interpret iron studies in context, recognize that ACD is a diagnosis of the underlying disease rather than an isolated hematologic problem, and resist the urge to treat the lab values rather than the patient.