Can a Blood Donation Detect Babesia? A Missed Diagnosis
How regional blood donor screening can identify Babesia
Why subtle symptoms may be overlooked
How reliable Babesia nucleic acid testing is
Can donating blood detect Babesia? Sometimes. Blood donation centers in parts of the United States where Babesia transmission is considered a significant risk routinely screen donated blood using nucleic acid testing (NAT). This screening is designed to protect transfusion recipients—not to diagnose illness—but it can occasionally identify an infection that had not previously been recognized.
Under current FDA guidance, year-round Babesia testing is recommended for donations collected in 14 states and Washington, D.C., rather than for every blood donation collected nationwide. Screening practices may therefore depend on where the blood is collected and the policies followed by the blood establishment.
This case illustrates how one man’s unexplained symptoms were finally linked to Babesia after he donated blood. His experience also highlights why babesiosis can be difficult to recognize when symptoms develop gradually, fluctuate, or resemble more common medical conditions.
Key points
- Not every blood donation in the United States is routinely tested for Babesia.
- FDA guidance recommends regional, year-round Babesia testing in areas with substantial risk.
- Babesia nucleic acid testing is highly sensitive, but no laboratory test detects every infection.
- Blood donor screening protects recipients and should not be used as a substitute for medical evaluation.
What Diseases Do Blood Banks Test For?
Blood establishments test donated blood for infectious agents that could be transmitted through transfusion. Testing requirements and procedures may vary by country, geographic risk, type of donation, and blood collection organization.
In the United States, donated blood may be screened for infectious agents that include:
- Human immunodeficiency virus (HIV)
- Hepatitis B virus
- Hepatitis C virus
- Human T-cell lymphotropic virus (HTLV)
- Syphilis
- West Nile virus
- Trypanosoma cruzi, which causes Chagas disease
- Babesia species in regions covered by FDA screening recommendations
The exact list should not be viewed as identical at every blood bank or for every donation. Some testing is universal, while other screening is based on regional risk, seasonal risk, donor history, or applicable blood-safety policies.
Routine blood donor screening does not include testing for Lyme disease. A person who may have Lyme disease or another tick-borne illness needs a separate clinical evaluation and appropriate diagnostic testing.
Babesia Diagnosed by a Blood Bank
He never imagined that his story would become an example of Babesia identified through blood bank screening. What began as a simple act of generosity—rolling up his sleeve to donate blood—became the turning point in a months-long medical mystery.
About a week after his donation, he received a letter explaining that the donated blood had tested positive for Babesia.
Your blood donation has tested positive for Babesia.
In that moment, he learned that blood donor screening had identified a possible explanation for symptoms that had persisted throughout the summer.
A reactive blood donor screening result generally requires appropriate follow-up and should not be treated as a complete clinical evaluation by itself. In this case, however, the notification finally brought Babesia into consideration.
Early Symptoms Pointed Toward Babesia
The earliest signs of illness appeared quietly.
As warmer weather arrived, he began experiencing brief episodes of unsteady breathing and momentary dizziness. At times, the world seemed to tilt before quickly settling again. Because the episodes were brief, they did not initially appear urgent.
These symptoms were not specific to Babesia, but in retrospect they were compatible with the infection that would later be identified through blood donor screening.
At his first clinic visit, he described the unusual sensations. The clinician recommended reducing stress, drinking more fluids, and cutting back on caffeine. He followed the advice, but the episodes continued.
Babesiosis does not always begin with a dramatic fever or an obvious medical emergency. Depending on the individual and the severity of infection, possible symptoms can include:
- Fatigue
- Sweating or night sweats
- Chills or fever
- Headache or body aches
- Dizziness or lightheadedness
- Breathlessness or a sensation of air hunger
- Reduced exercise tolerance
These symptoms overlap with many other conditions. Air hunger and dizziness, in particular, are not specific to Babesia and require a broader medical evaluation.
When the Story Changed—but Testing Still Did Not Happen
As summer progressed, his symptoms evolved.
Night sweats interrupted his sleep. Exhaustion lingered throughout the following day. He had trouble concentrating, his thoughts sometimes seemed to loop, and his mood became increasingly flat. Tasks that had once felt routine became more difficult.
He returned to his physician hoping someone would connect the growing list of symptoms.
Instead, he was told that anxiety, depression, or emotional stress might explain how he felt. A therapy referral was offered. Babesia testing was not ordered because a tick-borne infection had not been considered.
Psychological symptoms should not automatically be attributed to an infection, but neither should evolving physical symptoms be dismissed simply because changes in mood or concentration are also present. A careful evaluation should consider medical, neurologic, psychiatric, medication-related, and environmental explanations.
Babesiosis may contribute to fatigue, disrupted sleep, reduced exercise tolerance, and a general sense of illness. These effects can indirectly influence concentration and mood, but such symptoms remain nonspecific and do not establish the diagnosis.
When the Blood Bank Provided an Answer
The answer arrived only after he donated blood.
The blood establishment’s screening program detected Babesia nucleic acid in his donation. Rather than finding the infection because a clinician had suspected babesiosis, the result emerged through testing intended to prevent transfusion-transmitted infection.
The blood bank notification did not replace a clinical evaluation, but it provided a critical lead. Babesia could now be considered alongside his symptoms, exposure history, and any follow-up laboratory findings.
Suddenly, several parts of his illness appeared to fit together:
- Episodes of breathlessness
- Dizziness
- Night sweats
- Fatigue
- Reduced exercise tolerance
- Poor sleep
- Difficulty concentrating
He felt relief at finally having a possible explanation—and frustration that the clue had emerged through blood donation screening rather than during his earlier medical visits.
Is Every Blood Donation Tested for Babesia?
No. Babesia donor screening is not performed uniformly on every blood donation collected throughout the United States.
FDA guidance recommends year-round testing of donations collected in states and jurisdictions considered to have a substantial risk of transfusion-transmitted babesiosis. The regional recommendations have covered Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, Wisconsin, and Washington, D.C.
Blood collected elsewhere may not undergo routine Babesia NAT under the same regional testing recommendation. Screening policies can also evolve as Babesia expands geographically, additional surveillance information becomes available, and new blood-safety technologies are introduced.
For this reason, it is more accurate to say that blood establishments in designated Babesia-risk regions routinely use NAT rather than saying that all blood banks nationwide test every donation for Babesia.
A 2026 American Red Cross report illustrates an important limitation of this regional approach. From October 2021 through December 2025, investigators identified four cases of transfusion-transmitted babesiosis involving red blood cell donations collected in states where routine Babesia screening was not being performed. In each case, the donor had traveled to or lived in a Babesia-endemic state before donating blood elsewhere. These cases suggest that regional screening has dramatically reduced transfusion-transmitted babesiosis but cannot completely eliminate the risk created when donors cross geographic screening boundaries.
How Does Babesia NAT Work?
Nucleic acid testing looks for genetic material from the parasite in a whole-blood sample. Depending on the specific FDA-approved assay, the test may detect Babesia DNA or RNA.
Some donor-screening assays were developed specifically to detect Babesia microti, the species responsible for most human babesiosis in the United States. A newer FDA-licensed assay is designed to detect RNA from several species, including:
- Babesia microti
- Babesia duncani
- Babesia divergens
- Babesia venatorum
Therefore, statements about what “Babesia NAT” detects should account for the particular assay being used. Not every molecular test has identical species coverage or performance characteristics.
How Reliable Is Babesia NAT?
Babesia NAT is considered highly sensitive for blood donor screening and can identify low levels of parasitemia that may be difficult to detect reliably on a routine blood smear. This is particularly important because some infected donors have few symptoms or no symptoms at all.
However, “highly sensitive” does not mean perfect. The likelihood of detection can be influenced by:
- The specific assay used
- The Babesia species present
- The number of parasites circulating in the blood
- The timing of sample collection
- The condition and handling of the specimen
If parasite levels are below the assay’s limit of detection, an infection may not be identified. In addition, an assay designed primarily for Babesia microti should not automatically be assumed to detect every less-common Babesia species.
A negative NAT result therefore lowers the likelihood of detectable parasitemia in that particular sample but does not prove that Babesia infection has never occurred. A positive donor-screening result also requires appropriate follow-up and clinical interpretation.
For patients with suspected babesiosis, clinicians may consider molecular testing, examination of peripheral blood smears, serology, complete blood counts, liver tests, and markers of hemolysis depending on the clinical presentation. No single test should be interpreted without considering symptoms, exposure risk, timing, and other laboratory findings.
Why Blood Banks Screen for Babesia
Babesia infects red blood cells and can be transmitted through transfusion. An infected donor may feel well enough to donate blood while still carrying parasites in the bloodstream.
Transfusion recipients may be particularly vulnerable because many are older, immunocompromised, critically ill, or without a functioning spleen. Babesiosis acquired through transfusion can therefore cause serious illness.
Regional Babesia screening has dramatically reduced the risk of transfusion-transmitted babesiosis by identifying infected donations before they reach vulnerable recipients. However, as recent reports demonstrate, occasional travel-related cases can still occur when infected donors give blood outside regions where routine Babesia screening is performed.
Blood donor NAT is intended to identify potentially infectious donations before those blood components reach patients. Its purpose is blood safety—not to provide members of the public with a convenient diagnostic test.
Someone who suspects Babesia should not donate blood to obtain testing. The appropriate step is to seek clinical evaluation.
Babesia Can Be Present Without Classic Findings
Looking back, this patient’s symptoms were compatible with Babesia, but they were not diagnostic on their own. His body had been signaling that something was wrong through subtle and seemingly unrelated symptoms.
Babesiosis does not always produce the same presentation. Some patients develop fever, chills, sweating, fatigue, body aches, thrombocytopenia, or hemolytic anemia. Others may have a milder or less recognizable illness.
A normal hemoglobin level or the absence of obvious hemolytic anemia does not, by itself, exclude Babesia. At the same time, symptoms such as air hunger, dizziness, fatigue, sleep disturbance, or cognitive difficulty have many possible causes and should not automatically be attributed to the infection.
The diagnosis depends on the complete clinical picture and appropriate laboratory evidence—not on one symptom alone.
Frequently Asked Questions
Can donating blood detect Babesia?
Sometimes. Blood establishments in designated Babesia-risk regions use nucleic acid testing to screen donations. This testing occasionally identifies an infection that the donor did not know was present. Blood donation should never be used as a substitute for diagnostic testing.
Do all blood banks test for Babesia?
No. FDA recommendations use a regional approach. Year-round Babesia testing is recommended for donations collected in designated states and jurisdictions where the risk of transfusion-transmitted babesiosis is considered significant. Screening is not necessarily performed on every donation collected elsewhere in the United States.
How accurate is the Babesia NAT used by blood banks?
FDA-licensed donor NAT assays are highly sensitive and are capable of detecting low-level parasitemia, including in donors who have no obvious symptoms. Nevertheless, no NAT is 100% sensitive. Performance depends on the assay, Babesia species, parasite level, and timing of testing.
Is NAT more sensitive than a blood smear?
NAT can generally detect lower levels of parasitemia than routine microscopic examination of a blood smear. A smear remains useful because it can demonstrate parasites directly and help estimate the percentage of infected red blood cells. The two methods serve different purposes and may be used together during a clinical evaluation.
Does a negative Babesia NAT rule out infection?
No test rules out every infection with complete certainty. A negative NAT means Babesia nucleic acid was not detected in the sample. Very low parasite levels, differences in species coverage, or the timing of testing may affect detection. Results should be interpreted in the context of the patient’s symptoms and exposure history.
Does a positive blood donor screen prove that symptoms are caused by Babesia?
A positive donor-screening result provides important laboratory evidence of infection, but a clinician should still evaluate whether Babesia explains the person’s current symptoms. Other illnesses may be present at the same time.
What diseases do blood banks test for?
Blood establishments screen donated blood for multiple transfusion-transmitted infections, including HIV, hepatitis B, hepatitis C, syphilis, and West Nile virus. Testing for Babesia and certain other agents may depend on geographic risk, donor history, and current blood-safety policies.
Do blood banks test donated blood for Lyme disease?
No. Routine blood donor screening does not include Lyme disease testing. Babesia is handled differently because the parasite infects red blood cells, can persist in donated blood, and can be transmitted to a recipient through transfusion.
Can donating blood reveal an infection you did not know you had?
Yes, occasionally. Blood donor screening may identify certain infections in people who did not know they were infected. However, the screening program is designed to protect recipients and does not test donors for every possible infectious disease, medical condition, sexually transmitted infection, or cancer.
Can Babesia cause symptoms without a high fever?
Yes. Although fever is common in symptomatic babesiosis, its absence does not exclude infection. Some patients have a milder or more gradual illness with fatigue, sweating, dizziness, breathlessness, or reduced exercise tolerance. These symptoms are nonspecific and require a broader evaluation.
Clinical Perspective
This case is a reminder that babesiosis may present gradually and without every classic finding. When a patient who lives in or has traveled to a tick-endemic area develops otherwise unexplained sweats, fatigue, exercise intolerance, dizziness, fever, or breathlessness, Babesia may deserve consideration as part of the differential diagnosis.
At the same time, a blood donor NAT result should not be used to conclude automatically that every symptom is due to Babesia. The result needs to be interpreted alongside the patient’s medical history, examination, exposure risk, blood counts, markers of hemolysis, and additional diagnostic testing when appropriate.
Earlier recognition may shorten the time to diagnosis and treatment while helping prevent an infected blood donation from reaching a vulnerable transfusion recipient.
Related Articles
References
- Centers for Disease Control and Prevention. Babesiosis.
- Centers for Disease Control and Prevention. Clinical Overview of Babesiosis.
- U.S. Food and Drug Administration. Recommendations for Reducing the Risk of Transfusion-Transmitted Babesiosis.
- U.S. Food and Drug Administration. Recommendations for Reducing the Risk of Transfusion-Transmitted Babesiosis: Guidance for Industry.
- U.S. Food and Drug Administration. Procleix Babesia Assay.
- U.S. Food and Drug Administration. Babesia microti NAT for Blood Screening.
- Vannier E, Krause PJ. Human babesiosis. Int J Parasitol. 2019;49(2):89-102.
- Drews SJ, O’Brien SF, et al. Transfusion-transmitted Babesia species: an updated review. J Clin Microbiol. 2023.
- Amato M, Siller A, Schennach H. Babesiosis and Its Significance in Transfusion Medicine. Transfus Med Hemother. 2025.
- Townsend R, Losco P, Tonnetti L, et al. Transfusion-transmitted babesiosis in the era of regional Babesia screening: lessons from travel-associated donations. Transfusion. 2026.
- America’s Blood Centers. Final Babesia Guidance Published by FDA.
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
