Can a UTI Cause Anemia? Explaining the Connection

Urinary tract infections can indeed contribute to anemia, and they do so through more than one route. The bacteria behind most UTIs produce toxins that directly destroy red blood cells, the body’s inflammatory response locks away iron to fight the infection, and even some of the antibiotics prescribed to treat UTIs can lower hemoglobin in susceptible people. The relationship is more layered than a simple cause-and-effect, and certain groups face higher risks than others.

How UTI Bacteria Destroy Red Blood Cells

The most direct way a UTI leads to anemia is through hemolysis, the physical destruction of red blood cells. The bacterium responsible for the majority of UTIs is uropathogenic Escherichia coli (UPEC), and many UPEC strains secrete a toxin called alpha-hemolysin. As the name suggests, this toxin punches holes in red blood cell membranes, causing them to burst.¹ When enough red blood cells are destroyed faster than the bone marrow can replace them, hemoglobin drops and anemia sets in.

This hemolytic effect tends to matter most in kidney infections rather than simple bladder infections. A study of pregnant women hospitalized with pyelonephritis (a UTI that has ascended to the kidneys) found that their erythropoietin levels, the hormone that stimulates red blood cell production, were not suppressed at all compared to healthy pregnant women. The researchers concluded that hemolysis, not impaired red blood cell production, was the primary driver of anemia in those patients.² In other words, the body was still trying to make red blood cells at a normal rate. The problem was that bacteria were destroying them too quickly.

The Inflammation Pathway

Even without dramatic red blood cell destruction, a UTI can gradually pull hemoglobin downward through inflammation. When the immune system detects a bacterial invasion, it ramps up production of signaling molecules that trigger a cascade of defensive changes. One of the most consequential involves a hormone called hepcidin, produced by the liver. Hepcidin’s job is to block iron from entering the bloodstream, essentially hiding it from invading bacteria that need iron to multiply.

The trouble is that your bone marrow also needs iron to build new red blood cells. Research comparing hepcidin levels across different types of anemia has shown that people with anemia driven by infection or chronic disease have significantly elevated hepcidin, while people with simple iron-deficiency anemia have extremely low levels.³ So during an active UTI, especially one that lingers or recurs, the body’s own defense strategy starves the bone marrow of the raw material it needs. A mild, short-lived UTI that clears quickly is unlikely to push this mechanism far enough to cause noticeable anemia. But a persistent, recurrent, or severe infection can.

The Battle Over Iron

The hepcidin response is part of a broader tug-of-war between your body and the bacteria over iron. UPEC bacteria have evolved sophisticated systems for scavenging iron from the tissues they infect, because iron is essential for their survival and reproduction.⁴ Your body counters by sequestering iron away from tissues where bacteria are present, a strategy sometimes called nutritional immunity.

Animal research has shown just how central iron is to UTI outcomes. In a mouse model, animals fed a low-iron diet had significantly lower bacterial loads in their bladders and less inflammation during a UTI. Meanwhile, mice genetically engineered to lack hepcidin (meaning they could not sequester iron) accumulated iron deposits, harbored more persistent bacteria, and mounted a heightened inflammatory response.⁵ The takeaway is that the same iron-limiting defense that helps your body fight the infection is also the mechanism that can tip you toward anemia if the fight drags on.

When the Antibiotic Causes the Anemia

Sometimes the connection between a UTI and anemia has nothing to do with the infection itself and everything to do with the drugs used to treat it. Two of the most commonly prescribed antibiotics for UTIs, nitrofurantoin and trimethoprim-sulfamethoxazole, carry well-documented risks of lowering blood counts in certain people.

Nitrofurantoin is an oxidant drug, and in people who have glucose-6-phosphate dehydrogenase (G6PD) deficiency, a common inherited enzyme shortage affecting hundreds of millions of people worldwide, it can trigger acute hemolytic anemia. A case report described a woman who developed a steep hemoglobin drop from 121 g/L to 89 g/L after just five days of nitrofurantoin for a routine UTI. Investigation revealed previously undiagnosed G6PD deficiency, and her anemia resolved after the drug was stopped.⁶ Both nitrofurantoin and trimethoprim-sulfamethoxazole carry warnings about this risk.⁷

Trimethoprim-sulfamethoxazole can also suppress the bone marrow more broadly. A documented case involved a 70-year-old woman who developed pancytopenia, a reduction in red blood cells, white blood cells, and platelets, after two weeks on the drug.⁸ This effect is more likely in older adults, people with kidney impairment, and those on prolonged courses. For most healthy adults taking a short course, significant blood count drops are unlikely. But if you notice unusual fatigue, pallor, or bruising while on either of these antibiotics, it is worth flagging to your doctor.

The medication angle also matters for people on long-term preventive antibiotics after organ transplants. A study comparing two drugs used after kidney transplants found that patients on dapsone were roughly twice as likely to develop acute anemia as those on trimethoprim-sulfamethoxazole, while UTI rates were similar between the two groups.⁹ For transplant recipients, drug choice involves carefully weighing infection prevention against the risk of worsening anemia.

UTIs and Anemia in Pregnancy

Pregnant women represent one of the groups where the UTI-anemia overlap is most clinically significant. Pregnancy already increases UTI risk because of anatomical changes to the urinary tract, and it simultaneously increases the demand for iron and red blood cells. When a UTI hits during pregnancy, the effects on hemoglobin can compound quickly.

Even asymptomatic bacteriuria, bacteria in the urine without any noticeable symptoms, has been linked to anemia in pregnancy when left untreated.¹⁰ When the infection progresses to pyelonephritis, the risks escalate further to include premature delivery, low birth weight, and more severe maternal anemia and blood abnormalities.¹¹

A study of pregnant women in Baghdad found that those with UTIs had a mean hemoglobin of 10.5 g/dL, and over half were anemic. The risk of anemia in pregnant women with a UTI was about four and a half times higher than in those without one. For women who had both a UTI and had been pregnant many times before, the risk climbed to nearly seven times higher. And strikingly, women with a UTI during their second trimester had roughly fifteen times the risk of anemia compared to controls.¹² These numbers reflect the combined vulnerability: pregnancy draws heavily on iron reserves, and a simultaneous infection accelerates the depletion.

The Elderly and the Two-Way Street

In older adults, the relationship between UTIs and anemia runs in both directions. UTIs are among the most common infections in people over 65, and anemia becomes increasingly prevalent with age for reasons that include chronic disease, nutritional deficits, and declining kidney function. These two conditions do not just happen to coexist; they appear to feed each other.

A large longitudinal study of elderly adults in India found a striking association. After adjusting for a wide range of health and socioeconomic factors, older adults with UTIs were nearly six times more likely to be anemic.¹³ The same study also identified anemia itself as a significant risk factor for developing a UTI in the first place. This makes biological sense: anemia can weaken immune function, making the urinary tract more susceptible to colonization by bacteria. And the resulting infection then worsens the anemia through the inflammatory and hemolytic mechanisms already described. Breaking this cycle often requires treating both conditions rather than focusing on one alone.

In children, a similar pattern has been observed. Anemia, along with immune factors like low immunoglobulin levels and anatomical abnormalities, was identified as an independent risk factor for recurrent UTIs in pediatric patients.¹⁴ The bidirectional dynamic, anemia raising UTI risk and UTIs worsening anemia, is not unique to the elderly. It shows up across age groups, though its clinical impact tends to be greatest at the extremes of life.

Rare but Serious Blood Complications

In a small number of cases, a UTI that progresses to sepsis can trigger a severe blood disorder called thrombotic microangiopathy, where tiny blood clots form in small vessels and shred red blood cells as they pass through. This results in a type of anemia called microangiopathic hemolytic anemia (MAHA), which can be life-threatening. A case series examining this complication found that UTIs were among the most common infection sources, alongside lower respiratory infections. Several of the patients also developed disseminated intravascular coagulation, where the clotting system goes haywire throughout the body. In that series, all patients recovered after receiving plasmapheresis, a treatment that filters the blood.¹⁵

These severe outcomes are uncommon with a straightforward lower UTI. They tend to occur when infections are missed, treatment is delayed, or the patient has underlying conditions that impair immune defenses. But they underscore why recurrent or persistent UTIs deserve medical attention rather than being shrugged off as a nuisance.

Recovering Hemoglobin After a UTI

For most people, anemia linked to a simple UTI resolves once the infection is cleared. The body stops producing excess hepcidin, iron becomes available to the bone marrow again, and hemoglobin gradually climbs back up. But “gradually” is the key word. Even after the infection is gone, it can take weeks to months for red blood cell counts to fully normalize, especially if iron stores were already marginal before the infection.

A large retrospective study examined whether giving intravenous iron during an acute infection could speed up hemoglobin recovery. Among patients with UTIs, those who received IV iron showed a hemoglobin increase of about 1.4 g/dL over the 60- to 90-day recovery period, compared to about 1.0 g/dL in those who did not receive it. The IV iron group also had modestly higher survival rates at both 14 and 90 days.¹⁶ This is noteworthy because clinicians have traditionally been reluctant to give iron during active infections, since bacteria need iron too. The emerging data suggest that in patients who are iron-deficient and infected, the benefit of replenishing iron may outweigh the theoretical risk of feeding the bacteria, though this remains an active area of research.

For people recovering from a UTI-related drop in hemoglobin at home, the practical advice is straightforward. Ensure adequate iron intake through diet or supplements if your doctor recommends them, stay hydrated, and follow up with blood work if fatigue and pallor linger well after the infection has resolved. If you have had repeated UTIs and persistent low-grade anemia, the two problems are likely reinforcing each other, and addressing iron status proactively may help break the pattern.

Telling Apart Iron Deficiency and Infection-Driven Anemia

One challenge doctors face when a patient has both a UTI and anemia is figuring out whether the anemia was already there before the infection or was caused by it. The distinction matters because the treatments differ. Simple iron deficiency responds well to iron supplements. Anemia driven by infection and inflammation will not improve until the underlying infection is treated, and piling on iron supplements during active infection may not help and could theoretically aid the bacteria.

Standard blood tests like serum ferritin can be misleading during an infection because ferritin rises as part of the inflammatory response, masking a true underlying iron deficit. More specialized markers, such as the ratio between soluble transferrin receptor levels and ferritin, have been studied as a way to distinguish infection-driven anemia from iron deficiency, especially in populations like infants where both are common.¹⁷ In practice, many people have a combination of both, pre-existing low iron reserves that were manageable until an infection pushed them over the edge into symptomatic anemia. Treating the infection first and then reassessing iron status a few weeks later is the common clinical approach.

Who Should Pay Attention

A single uncomplicated bladder infection in an otherwise healthy adult is unlikely to cause clinically meaningful anemia on its own. The people who face real risk are those at the intersection of multiple vulnerabilities:

• Pregnant women: Already iron-depleted from the demands of pregnancy, even a low-level urinary infection can meaningfully worsen anemia.
• Older adults: Chronic disease, reduced dietary intake, and slower immune responses create fertile ground for the UTI-anemia cycle.
• People with recurrent UTIs: Each episode reactivates the inflammatory iron-sequestration response, and repeated courses of antibiotics increase the chance of drug-related blood count effects.
• Those with G6PD deficiency: Common UTI antibiotics can trigger acute hemolysis, sometimes severe, in people with this enzyme deficiency who may not even know they have it.
• Immunocompromised patients: Organ transplant recipients, people on chemotherapy, or those with poorly controlled diabetes face both higher UTI rates and greater sensitivity to anemia.

If you fall into any of these groups and notice escalating fatigue, dizziness, or unusual paleness around the time of a UTI, a complete blood count is a reasonable thing to ask your doctor about. The fix is usually straightforward once the connection is recognized, but it requires someone to look for it.