Читать книгу Transfusion Medicine - Jeffrey McCullough - Страница 84

The physical examination of a potential donor includes determination of the donor’s temperature, pulse, blood pressure, weight, and hemoglobin. Each of these has FDA‐mandated limits. In addition, the donor’s general appearance and behavior are assessed for any signs of illness or the influence of drugs or alcohol. The skin at the venipuncture site is examined for signs of intravenous drug abuse, lesions suggestive of underlying disease, and local lesions that might make it difficult to cleanse the skin and thus lead to contamination of the blood unit during venipuncture.

There are weight requirements for donors because it is necessary to balance the amount of blood collected in relation to the donor’s estimated blood volume and also the amount of blood in relation to the volume of anticoagulant in the collection container. To integrate the volumes of blood collected with the weight ranges of donors, an arbitrary lower weight limit of 110 pounds has been established. There is no upper weight limit, although extremely obese potential donors may have other health problems or inadequate venous access that could preclude donation. The pulse should be regular and between 50 and 100 per minute, although potential donors who have a slower pulse related to involvement in an active exercise program may donate with approval of the transfusion medicine physician.

Although hemoglobin may still be estimated by a manual screening method in which a drop of blood is placed in a copper sulfate solution of a known specific gravity, in developed countries, automated microhematocrit is most often used, and in less well‐developed countries, a hemoglobin color scale can be used [32]. Noninvasive methods for hemoglobin are now available but have not yet become widely used. For any method, the recommended blood drop source is the finger, because blood from an earlobe puncture can have a falsely elevated hemoglobin [33, 34]. Factors that affect the rate of deferrals due to hematocrit are the proportion of female donors, smokers, African Americans in the donor population, altitude of the donation location, and source of blood sample (finger versus ear lobe). Because the hemoglobin fluctuates with temperature, being lower in hot weather, there may be an increase in deferrals because of low hemoglobin during the summer months [35]. Until recently, the same hemoglobin criterion was used for men and women (12.5 g/dL). This is within the normal range for Caucasian women [11.6–15.7 g/dL) but below the normal range for Caucasian men (13.3–17.2 g/dL). Most hemoglobin deferrals occurred in women, although many women with essentially normal hemoglobins have been deferred. In contrast, a hemoglobin of 12.5 g/dL may indicate mild anemia in a man. Although FDA guidance now recognizes that many women may safely donate with hemoglobin 12–12.5 g/dL, it also recommends that further, although unspecified, steps to prevent iron deficiency be taken if this lower cutoff is used because iron deficiency is prevalent in premenopausal women who are frequent whole blood donors [36, 37]. The screening hemoglobin values do not prevent iron‐deficient individuals (predominantly women) from donating [36, 38].

Low or absent iron stores occur in a significant percentage of frequent blood donors. Suggested approaches include further restrictions on the frequency of blood donation and/or providing iron supplementation. There is no uniform approach to donors deferred because of low hemoglobin. Approaches have included temporary deferral for 6 months, 3 days to 3 months, or variable length of deferral depending on the hemoglobin. There are no standard recommendations regarding serum ferritin testing and whether to provide iron supplementation or merely recommend this to the donors [39, 40]. Some blood centers have implemented programs to perform ferritin testing, which is considered a more reliable indication of iron status. These programs often focus on young donors, especially females who may be most susceptible to the effects of iron depletion [41, 42]. Two studies [43, 44] support the value of iron therapy in women without anemia.

Even in the absence of anemia, iron deficiency can have clinical effects, such as fatigue, decreased exercise capacity, and cognitive performance [45]. Strategies ranging from physician referral to providing educational material or even providing iron supplements have been tried, but no standard approach is in wide use. This has been an issue for years and could have major implications for donor availability [38, 39, 45].