Another stab at donor hemoglobin screening

In this issue of TRANSFUSION, Lotfi and coworkers1 from Germany describe an interesting approach to hemoglobin (Hb) screening for prospective blood donors. For first-time donors, a Hb determination was performed on a venipuncture sample obtained at least 6 weeks before donation with an automated hematology analyzer. For repeat donors, Hb determination on a postdonation venous sample with an automated hematology analyzer was used to qualify donors for their next donation. Hb criteria of 125 g per L for women and 135 g per L for men were used. The minimum donation interval was 56 days for men and 84 days for women. Donors with acceptable postdonation Hb results were permitted to make their next donation without predonation Hb screening, whereas those with a low postdonation Hb result were eligible to donate only after a predonation venous Hb determination. The authors evaluated the sensitivity and specificity of this approach for over 19,000 donors followed over a 3-year time period. In the final 7 months of the study, only 2.69 percent of donors were bled inappropriately. The vast majority of these were female donors with a Hb level of between 120 and 124 g per L. The mean difference in Hb levels between donations was 6 g per L. The authors concluded that the use of a venous Hb result obtained on previous donation was an acceptable alternative for performing donor Hb screening. Few subjects have generated as much frustration (or as many editorials in TRANSFUSION) as donor Hb screening.2-5 This is not surprising, given that insufficient Hb is the single major cause of donor deferrals, in an era of donor shortages. Although determination of donor Hb levels may be important to protect donor and recipient health, the rationale for the cutoff criteria used is unclear. The current criteria are set at 125 g per L for all whole-blood donors in Canada and the United States, 125 g per L for women and 135 g per L for men in European Union Blood Safety directives, and 120 g per L for women and 130 g per L for men in current UK and Australian criteria. The absence of consensus indicates the lack of a firm scientific basis for these differing regulatory requirements. As has been pointed out in many other editorials and commentaries, if the goal of Hb screening is to protect the anemic or borderline anemic donor, the cutoff level of 125 g per L is too high for women and too low for men, because the CDC has defined the lower limit of normal as 120 g per L for women and 136 g per L for men in a Caucasian nonsmoking population residing at sea level.2 Current minimum Hb requirements and unit-volume specifications are also not precise enough to achieve the goal of a standard Hb dose per unit of red cells.5 Most of the debate over changing the standard has focused on lowering the minimum Hb requirement for women from 125 g per L to 120 g per L, because up to 15 to 20 percent of women are deferred because of low Hb, many with a Hb in the range of 120 to 125 g per L. Supporters of a change to a lower Hb cutoff point out that these women have a completely normal Hb, and daily activities for those of us who are not competitive athletes would not be significantly influenced by a postdonation Hb level of 110 g per L. Opponents of lowering the standard point out that iron balance is precarious in women of childbearing age, and many repeat blood donors are found to have iron stores in the iron deficiency range. The debate has been raging on for many years, as witnessed by the “pro” and “con” articles published more than 15 years ago in the “Controversies in the Transfusion Medicine” section of TRANSFUSION.6,7 In addition to controversies over the appropriate Hb cutoff level, the measurement of donor Hb level before donation is problematic.8-10 Although a venous sample would be preferable for accuracy, obtaining the sample would subject the donor to another venipuncture, use a potential phlebotomy site, and contribute to the volume of blood drawn. Earstick capillary samples overestimate venous Hb levels.8 Fingerstick capillary sampling is also subject to inaccuracies and may be highly operator dependent. Each method in use including copper sulfate screening, microhematocrit testing, and Hb measurement with a portable hemoglobinometer has its own difficulties. Methods are often combined in algorithms to determine donor eligibility.10 Difficulties in donor Hb determination were elegantly summarized in an editorial by Cable2 in TRANSFUSION in 2003. Predonation Hb determination may also contribute to a decreased rate of donor return.11-13 A major challenge for blood collection agencies is to convert first-time or occasional donors into regular donors. The retention of first-time donors at Canadian Blood Services (CBS) is approximately 36 percent. Temporary deferral may discourage future donation attempts. As a rebuffed suitor may eventually give up in discouragement, donors who are temporarily deferred may be less likely to reattempt donation.12 This may be particularly true for donors who are told that they have “low iron” or “low blood” and perhaps need to conserve their own reserves. Although factors contributing to donor return are poorly understood, recent studies suggest that in addition to temporary deferrals, return rates are influenced by negative donation experiences, especially if they occur early in an individual's donation career.11,12 This is true not only for donors who have experienced a major reaction, but also those who have experienced minor adverse events such as bruising or mild fatigue after donation.13 We know from donor surveys and our own first-hand experience that fingerstick sampling to obtain a capillary blood sample is a most disagreeable part of the donation process. On a survey of more than 1000 CBS donors performed in March 2005, satisfaction with fingerstick capillary sampling, as determined by a rating of 9 or 10 of 10, was 57 percent, only slightly higher than the 51 percent satisfaction level with needle insertion to perform the actual phlebotomy. If willingness to return is indeed a balance between positive and negative elements associated with donation, fingerstick sampling may weigh in heavily on the negative side. For this reason, there is considerable interest in development of noninvasive methods of Hb determination, based on optical measurements of blood flow with a pneumatic finger cuff. Although preliminary results have been presented, none of these devices is currently licensed for blood donor screening. The study by Lotfi and colleagues in this issue of TRANSFUSION attempts to address this last difficulty, by eliminating predonation sampling for Hb determination.1 Unfortunately, measurement of donor satisfaction or return rates with this approach compared to traditional approaches was not part of this study. It is also possible that a venous Hb measurement after donation is actually a more accurate predictor of Hb at the next donation than a capillary sample obtained before donation, with a less accurate measurement such as a portable hemoglobinometer. No direct comparison was made between these two different screening approaches in the study. In a study by Wood and associated8 from the American Red Cross in Cleveland, Ohio, hematocrit was found to decrease by 1.7 units on comparison of predonation to postdonation results with venous samples obtained before and after a given phlebotomy.8 This study also found good concordance between predonation fingerstick microhematocrit results and postdonation venous Hb levels, with a mean discordance of 0.9 units when fingerstick overestimated venous Hb. Although very few donors in the study by Lotfi and colleagues appear to have been inappropriately phlebotomized, the interdonation interval of 134 days for male donors and 183 days for female donors was considerably shorter than that seen for a significant percentage of the donor population.1 At CBS, 30 percent of donors in our database have not donated for more than 18 months. As the predonation interval lengthens, clearly the predictive value of a previous Hb value will decrease. Determining the acceptable interval between donations and establishing two categories of repeat donors would add to the complexity of operationalizing this approach for a large blood center. The regulatory paradigm of subjecting each donor to identical testing and questioning at each and every donation, which is the current North American philosophy, would require revision before consideration of the type of approach suggested by these German authors. Nevertheless, in this era of increasingly stringent criteria for donor eligibility and ongoing need for blood components, it is refreshing to see novel approaches to donor Hb screening being developed.

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