What causes fever and low hemoglobin?

September 26, 2025 •

5 min read

According to the National Institutes of Health, chronic inflammatory conditions are the second most common cause of anemia worldwide. Learning what causes fever and low hemoglobin is key to understanding the complex interplay between inflammation, the immune response, and red blood cell production.

Quick Summary

Fever and low hemoglobin levels are often linked by an underlying inflammatory process, which can be triggered by infections, autoimmune diseases, chronic conditions, and some cancers. This inflammation affects red blood cell production, iron metabolism, and lifespan, leading to anemia while the body battles the primary issue.

Key Points

Inflammation is the link: Chronic inflammation from conditions like infections, autoimmune diseases, and cancer often causes both fever and low hemoglobin levels by affecting red blood cell production and iron usage.
Anemia of Chronic Disease (ACD): This is a common cause where inflammatory cytokines disrupt iron metabolism and suppress bone marrow function, leading to anemia.
Infections can cause both: Severe or chronic infections, such as malaria or sepsis, can directly or indirectly cause low hemoglobin and are frequently accompanied by fever.
Autoimmune disorders play a role: Diseases like lupus can trigger autoimmune hemolytic anemia, where the body's own immune system destroys red blood cells, alongside causing inflammation and fever.
Cancer as a potential cause: Malignancies, especially those affecting the blood and bone marrow, can cause anemia and a cancer-related fever through systemic inflammation or direct impact on blood cell production.
Seek medical attention for diagnosis: Because multiple serious conditions can cause this combination of symptoms, a medical evaluation is necessary to identify the underlying cause and determine the correct treatment.

Understanding the Connection Between Fever and Low Hemoglobin

A fever, or pyrexia, is a temporary increase in your body's temperature, often due to an illness. Hemoglobin is the protein in your red blood cells that carries oxygen from your lungs to the rest of your body. Low hemoglobin levels, a condition known as anemia, signify a reduced oxygen-carrying capacity in the blood. When these two seemingly distinct symptoms appear together, they are often pointing towards a more serious underlying systemic problem, with inflammation as the common link.

Anemia of Chronic Disease/Inflammation (ACD)

Anemia of Chronic Disease (ACD), also known as anemia of inflammation, is a highly prevalent type of anemia that occurs in people with chronic inflammatory conditions. It is the second most common form of anemia globally. The link is the inflammatory process itself, which triggers a complex series of physiological changes in the body. When a person has a long-term infection, autoimmune disease, or cancer, inflammatory cytokines are released. These cytokines disrupt iron metabolism, making it difficult for the body to utilize its stored iron to create new red blood cells. This is a survival mechanism that the body employs to limit iron availability to invading pathogens, though it inadvertently leads to anemia.

The specific mechanisms of ACD include:

Altered iron metabolism: Inflammatory signals increase the production of hepcidin, a hormone that blocks iron absorption and release from storage.
Impaired erythropoiesis: The bone marrow's ability to produce new red blood cells is suppressed, and its response to erythropoietin (a hormone that stimulates red blood cell production) is reduced.
Shortened red blood cell lifespan: The presence of inflammation can cause red blood cells to be destroyed sooner than their normal lifespan of around 120 days.

Infections Causing Fever and Low Hemoglobin

Acute and chronic infections are significant culprits behind the combined symptoms of fever and low hemoglobin. The infectious process, whether bacterial, viral, or parasitic, can provoke a strong inflammatory response that leads to ACD. Additionally, some pathogens have direct methods of causing anemia.

Examples of infectious causes:

Malaria: A parasitic infection transmitted by mosquitoes, malaria parasites directly infect and destroy red blood cells, leading to a type of hemolytic anemia. The cycle of red blood cell destruction often coincides with recurring high fevers and chills.
HIV/AIDS: This chronic viral infection can cause anemia through various mechanisms, including inflammation leading to ACD, direct suppression of bone marrow, and opportunistic infections.
Bacterial infections: Severe infections like sepsis can trigger a rapid onset of anemia due to massive erythrophagocytosis (macrophages eating red blood cells), as well as DIC (Disseminated Intravascular Coagulation), a condition that causes microangiopathic hemolytic anemia.
Viral illnesses: Viruses like Epstein-Barr (mononucleosis) or parvovirus B19 can also be linked to hemolytic anemia, with fever being a prominent symptom.

Autoimmune and Inflammatory Diseases

Autoimmune disorders are a common cause of chronic inflammation, making them prime candidates for causing fever and low hemoglobin. The immune system mistakenly attacks healthy cells, triggering the same inflammatory cascade seen in ACD.

Key conditions include:

Autoimmune Hemolytic Anemia (AIHA): In this specific condition, the immune system produces antibodies that attack and destroy the body's own red blood cells. Fever is often a symptom of this rapid red blood cell destruction.
Systemic Lupus Erythematosus (Lupus): Lupus is a multi-system autoimmune disease known for causing chronic inflammation. It can lead to anemia through ACD or by directly causing AIHA.
Rheumatoid Arthritis (RA): This autoimmune disease causes chronic inflammation of the joints but also leads to ACD, which is often a mild to moderate anemia.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis cause chronic inflammation of the digestive tract, which can lead to ACD and sometimes iron deficiency anemia from blood loss.

Malignancies (Cancers)

Various cancers, especially those affecting the blood and bone marrow, can cause both fever and low hemoglobin. The cancer itself can trigger an inflammatory response, and treatments can also contribute to anemia.

Cancer-related causes include:

Hematological Malignancies: Cancers like leukemia and lymphoma originate in the blood or bone marrow and can directly suppress or displace the bone marrow's ability to produce healthy blood cells, including red blood cells. Neoplastic fever, a fever caused by the cancer itself, is common.
Solid Tumors: Even solid tumors can secrete substances that cause a systemic inflammatory response, leading to ACD. In some cases, chronic blood loss from a gastrointestinal tumor can also cause iron deficiency anemia.

Comparison Table: Causes of Fever and Low Hemoglobin


Cause	Mechanism of Anemia	Inflammatory Response	Typical Fever Pattern	Examples
Chronic Infection/Disease	Impaired iron metabolism, suppressed erythropoiesis, shortened RBC lifespan.	Chronic, low-grade.	Intermittent, often low-grade.	HIV/AIDS, TB, Chronic Kidney Disease.
Acute Infection	Hemolysis, sepsis-related, bone marrow suppression.	Acute, high-grade.	Sudden, high spikes.	Malaria, Severe Sepsis.
Autoimmune Disorders	Autoimmune hemolysis (AIHA), chronic inflammation (ACD).	Acute or chronic.	Variable, depends on activity.	Lupus, Rheumatoid Arthritis.
Malignancies	Bone marrow suppression, chronic inflammation (ACD), blood loss.	Chronic.	Neoplastic fever (irregular).	Leukemia, Lymphoma.

What to do if you have these symptoms

If you are experiencing a persistent or recurring fever coupled with symptoms of anemia like fatigue, weakness, or pale skin, it is crucial to consult a healthcare professional. A doctor will conduct a thorough medical evaluation, including a physical exam and blood tests like a complete blood count (CBC). Further diagnostic testing may be necessary to identify the underlying cause. Treatment will then focus on managing the primary condition that is causing both the fever and the low hemoglobin. For more information, the National Institutes of Health provides comprehensive health information on blood diseases: https://www.niddk.nih.gov/health-information/blood-diseases.

Conclusion

Fever and low hemoglobin are not isolated issues; they are often linked by an underlying inflammatory process caused by conditions ranging from infections to chronic illnesses and malignancies. The body’s inflammatory response, while intended to fight off threats, can disrupt red blood cell production, iron metabolism, and cell lifespan, resulting in anemia. Identifying the root cause is the key to proper treatment and resolution of these complex, related symptoms. A medical diagnosis is always necessary to determine the appropriate course of action.

Frequently Asked Questions

A severe viral infection like the flu can cause a temporary, mild decrease in hemoglobin due to inflammation. However, a persistent or significant drop in hemoglobin combined with fever is not typical and warrants further investigation for a more serious underlying cause.

Anemia of Chronic Disease (ACD) is caused by inflammation that prevents the body from properly using its iron stores, even if stores are normal or high. Iron deficiency anemia is caused by a true lack of iron in the body, often due to poor diet or blood loss.

In autoimmune hemolytic anemia (AIHA), the immune system produces antibodies that destroy red blood cells, leading to a rapid drop in hemoglobin. Other autoimmune diseases, like lupus, cause general chronic inflammation that can lead to anemia of chronic disease, with fever as a symptom.

You should see a doctor if you experience persistent or recurring fevers accompanied by symptoms of anemia, such as extreme fatigue, paleness, or shortness of breath. A diagnostic workup is necessary to find and treat the underlying cause.

A doctor will likely order a complete blood count (CBC) to check hemoglobin and other blood cell levels. They might also order inflammatory markers like C-reactive protein (CRP), tests for autoimmune antibodies, or specific panels to check iron levels and metabolism.

Yes, certain cancers, particularly leukemia and lymphoma, can cause both symptoms. Cancer can cause a persistent fever (neoplastic fever) and suppress the bone marrow's ability to produce healthy blood cells, including red blood cells.

Yes, some medications can cause both symptoms. Certain antibiotics or other drugs can lead to drug-induced hemolytic anemia, where red blood cells are destroyed. Additionally, the body's reaction to some medications can cause a fever.