Feature Articles

Advising Blood Donors About Anemia and Deferral Due to Low Hematocrit

April 2, 2009

Doctor advising patientAlmost all of the blood used for transfusions in the United States is donated by volunteers, who are screened for health risks that might make the donation unsafe for either the donor or the recipient. Of these roughly one million monthly blood donors, about 10% are deferred from donation because their hematocrit level falls below the FDA-mandated threshold of 38%.1 This deferral may be the first time donors discover that they have anemia or are considered borderline anemic.

Concerned about their health and their ability to donate, some deferred donors may consult their doctors and other medical professionals to find out how to raise their blood counts and to check to make sure their anemia is not a signal of a more serious health issue. More worrisome though are the numerous blood donors who do not inform their doctors about their deferral or low hematocrit score. In both circumstances, close communication with patients about their medications, symptoms, and low hematocrit levels will help you develop and help your patient understand the best plan of action to prevent or treat anemia.

Why a Low Hematocrit Level Leads to Deferral

Several intricacies related to stored iron and measuring hematocrit levels can be confusing for deferred blood donors who may have only been told, “Sorry, we can’t accept you, your blood count is too low.” With little or no additional information from the donation center, other healthcare professionals often play a large role in determining if the patient is actually anemic and educating them about blood donation. A few facts to relay to your patients, which may help them understand how a low hematocrit level leads to deferral, include:

Hematocrit Threshold for Blood Donation
Blood donors are required to have a hemoglobin level of at least 12.5 g/dL or hematocrit of 38% in order to donate blood.2 This is to ensure that donors have an adequate number of red blood cells (RBCs) for donation as well as adequate iron stores for erythropoiesis following donation. Being deferred from donation due to a low hematocrit during screening does not always mean the patient is anemic or has a medical problem. For example, male donors with a hematocrit below the acceptable 38% are considered anemic, but nonanemic women within the normal hematocrit range of 36-37% are not able to donate blood. Although this practice turns away nonanemic women from donating blood, it reduces the chance of depleting their iron stores and potentially causing anemia following donation. Men are allowed to donate when slightly anemic becuase it is much easier for them to replace the iron lost during donation.

Hematocrit threshold graphicDonating Blood Can Cause Iron Deficiency
A healthy blood donor loses about 200-250 mg of iron per blood donation, constituting a roughly 6% and 9% iron loss for men and women with an average of 4.0g and 2.5g total body iron, respectively.3 A double RBC donation, permitted every 16 weeks, results in the loss of up to 500 mg. The body compensates for this loss by mobilizing iron stores in the form of ferritin. For this reason, mean ferritin levels are significantly lower in blood donors than in non-donors and studies have shown that iron stores decline with repeated blood donation.4 Men usually have the most dramatic drop in ferritin levels because of higher iron stores before donation. After 6-8 phlebotomies the ferritin level is about 40% lower than at baseline.4 The proportion of male donors with decreased iron stores went from 8 to 19% with an increase from 5 to 6 donations per year.4

Differences in Screening Methods
There is no consensus among blood banks on the best method for blood donor anemia screening.5 In hospitals and laboratories, the gold standard for hemoglobin detection is the hemiglobincyanide method provided by automatic hematology analyzers.6 Screening tests for potential blood donors however require quicker, easier, and more cost-effective testing methods that do not require a venipucture. Three tests which are commonly used for primary screening are the CuSO4 method, the use of portable equipment that is able to spectrophotometrically determine hemoglobin, and microhematocrit which uses a capillary tube and a high-speed centrifuge.7 While these tests are quick, easy, and relatively inexpensive, their sensitivity, specificity, and accuracy are lower than that of automatic hematology analyzers.7 These tests are discussed in detail below.

Differences in Screening Tests for Iron Levels

CuSO4 (copper sulfate)
This is a qualitative screening test based on specific gravity. The density of the drop of blood is directly proportional to the amount of hemoglobin it contains. The sample of donor's blood dropped into copper sulfate solution becomes encased in a sac of copper proteinate, which prevents any change in the specific gravity for about 15 seconds. If the hemoglobin is equal to or more than 12.5 gm/dL the drop will sink within 15 seconds and the donor is accepted. If the blood drop sinks to the middle and remains or starts to rise, a microhematocrit or comparable test is usually used to confirm the deferral. This is not a quantitative test and will only show that the hemoglobin is equal to, below, or above acceptable limits. Test results that indicate satisfactory hemoglobin levels are usually accurate, but some results that indicate low hemoglobin levels can be false. Repeating the test by a second method is sometimes used as confirmation.7

Microhematocrit using Hematostat or a comparable test
Microhematocrit is a method for rapid determination of hematocrit done on an extremely small quantity of blood (one capillary tube of approximately 10 µL) by use of a capillary tube and a high-speed centrifuge. This method is a little more time consuming than other methods. Microhematocrit is often used to confirm failures with the CuSO4 method. A recent study shows a relatively poor correlation of the microhematocrit with the automated hematology analyzer. Anemia screening using this method failed to detect 35.7% of truly anemic donors.7

Hemoglobin screening using HemoCue or a comparable test
Some blood centers currently use portable equipment that is able to spectrophotometrically determine hemoglobin. These devices use a 10 µL capillary blood sample to determine hemoglobin by measuring the absorbance of azide methhemoglobin, using a cuvette containing a dry reagent system and a dual wavelength photometer. There was a relatively poor correlation of HemoCue 201(+) with the automated hematology analyzer. However, this method was more accurate (56%) in detecting anemia in prospective female blood donors than the microhematocrit method.7 The HemoCue 201(+) and the microhematocrit method were equivalent in their donor deferral rate.

Diagnosing and Managing Anemia After Deferral

It is also important to inform patients that a low hematocrit is not an arbitrary measurement only related to blood donation. Rather, a low hematocrit level or anemia may be an important diagnostic sign that points to a serious and possibly treatable medical condition. The symptoms of anemia can include headache, fatigue, weakness, and difficulty in thinking. With severe anemia, other symptoms, such as shortness of breath and rapid heartbeat, may be experienced. There are several possible reasons that a patient may be anemic and they generally include iron and vitamin deficiencies, chronic illnesses, and gastrointestinal bleeding. Differentiating the types of anemia is important in planning diagnostic testing and in guiding therapy.

Iron and Vitamin Deficiency Anemia
Because it is the most common cause of anemia, iron deficiency must be considered in the evaluation of any anemic patient. Depending upon the criteria used for the diagnosis of iron deficiency, approximately 4-8% of premenopausal women are iron deficient. In men and postmenopausal women, iron deficiency is uncommon in the absence of bleeding.2 Oral iron supplements, and less frequently, parenteral iron, are used to treat iron deficiency. Supplements are especially important when a patient is experiencing clinical symptoms of iron deficiency anemia to replenish normal iron stores to raise hematocrit levels. A complete overview of oral iron supplements can be found in feature articles: A Physician’s Guide to Oral Iron Supplements and A Patient’s Guide to Oral Iron Supplements.

Existing Chronic Illness and Gastrointestinal Condition
Patients with an existing chronic illness or gastrointestinal (GI) condition are at risk for a low hematocrit level and anemia. If the underlying chronic illness can be effectively treated, the anemia often improves. Conditions such as infections, inflammation, and cancer particularly suppress production of red blood cells in the bone marrow. Renal insufficiency or damage can also lead to low hematocrit level and anemia. There are no specific laboratory tests, so the diagnosis is typically made by excluding other causes. No specific treatment exists for this type of anemia, so treatment of the underlying disorder is usually the first step. Erythropoiesis-stimulating agents (ESAs) may be used to treat more severe cases.8

Another doctor advising a patientConditions affecting the digestive tract can often cause bleeding, which commonly lead to anemia. Some conditions which can cause GI bleeding include stomach ulcers, growths in the intestine (polyps), colon cancer, and other less common diseases of the digestive tract. Certain medications can also cause bleeding of the digestive tract. Detection and correction of the source of GI bleeding is the first and most important step in treatment.

Unknown Chronic Illnesses or Gastrointestinal Blood Loss
Anemia is an important sign that can point to a serious and possibly treatable medical condition, such as GI bleeding or a chronic illness like kidney disease or cancer. Non-menstruating women with a blood count below 36%, and men with a blood count below 38% should be evaluated further if they donate blood fewer than 3 times per year and are not already under care for a chronic illness or condition of the digestive tract. Failure to recognize and evaluate anemia in these patients could lead to delayed diagnosis of treatable conditions.

Although being deferred from donation can be frustrating for the patient, it can call attention to a serious medical condition which otherwise would have gone unnoticed. It may also represent an opportunity for you to educate them on the need for a healthy lifestyle, including a balanced iron-rich diet, and vitamins or supplements if needed. With the right information and help from you, many deferred blood donors can learn how to raise their blood counts, stay healthy, and try to donate again.


  1. BloodCenter of Wisconsin. Donating Blood, Investigators: Alan E. Mast, M.D., Ph.D. Accessed: February 2, 2009. Link.
  2. Conrad M. Iron Deficiency Anemia. Accessed: March 18, 2009. Link.
  3. Temper BJ. Minerals, the Central Nervous System and Behavior. In: Worobey J, Temper BJ, Kanarek RB, eds. Nutrition & Behavior: a Multidisciplinary Approach. Cambridge, MA: CABI Publishing; 2006:100. Link.
  4. FDA Blood Products Advisory Committee. Iron Status in Blood Donors. 92st Meeting, September 10-11, 2008. Accessed: March 18, 2009. Link.
  5. Cable RG. Hemoglobin determination in blood donors. Transfus Med Rev. 1995 Apr;9(2):131-44. Link.
  6. Clinical and Laboratory Standards Institute. Reference and selected procedures for the quantitative determination of hemoglobin determination in blood; approved standard. 3rd ed. Wayne, PA: NCCLS; 2000. Link.
  7. Mendrone Jr A, Sabino EC, Sampaio L, Neto CA, Schreiber GB, de Alencar Fischer Chamone D, Dorlhiac-Llacer PE. Anemia screening in potential female blood donors: comparison of two different quantitative methods. Transfusion. 2009 Jan 2. Link.
  8. The Merck Manual. Anemia of Chronic Disease. Accessed: March 2, 2009. Link.