Evaluation of a point-of-care method for screening blood donors for sickle cell status
Abstract
BACKGROUND
Turbidity tests are commonly used for screening blood units for the presence of sickle cell trait (SCT) before transfusion to specific patient populations, based on recommendations of the AABB. In this pilot study, we evaluate a new method for screening blood donors and blood units for the presence of sickle hemoglobin.
STUDY DESIGN AND METHODS
This study was based at King Abdulaziz University Hospital in Jeddah, Saudi Arabia. Study participants were approached consecutively between July 24, 2016, and August 8, 2016. Blood donors, control individuals, and known patients with sickle cell disease (SCD) were tested using both a point-of-care testing technology (Sickle SCAN, Biomedomics, Inc.) and hemoglobin capillary electrophoresis (HEP). Corresponding blood units were also tested using Sickle SCAN.
RESULTS
A total of 200 donors, 13 blood units, and 57 patients and controls were included. Sensitivity and specificity of Sickle SCAN for detection of SCT and SCD was 100%, when compared to HEP as the gold standard.
CONCLUSION
Sickle SCAN is a rapid test that shows high sensitivity and specificity for identification of hemoglobin S among blood donors and when used for testing blood units.
ABBREVIATIONS
-
- HEP
-
- hemoglobin capillary electrophoresis
-
- KAUH
-
- King Abdulaziz University Hospital
-
- POC
-
- point-of-care
-
- SCD
-
- sickle cell disease
-
- SCT
-
- sickle cell trait
In sickle cell disease (SCD), the presence of the abnormal hemoglobin S results in chronic hemolysis and generalized inflammation. Management of the clinical complications of SCD is often challenging and complex. Blood transfusion can be lifesaving in aplastic crisis, splenic sequestration, and acute chest syndrome.1, 2 Transfusion is the mainstay of management in ischemic stroke, a devastating complication of SCD, and chronic transfusion regimens prevent stroke recurrence in a considerable proportion of patients.3, 4
Based on the recommendations of the AABB, red blood cell (RBC) units collected from donors with sickle cell trait (SCT) should not be used for transfusion of patients with SCD,5 since the main goal of transfusion therapy in patients with SCD is reduction of HbS level. RBC units prepared for intrauterine transfusions should also be HbS negative.6
There are other potential benefits of screening RBCs for the presence of HbS, as leukofiltration failure has been reported with SCT blood.7 Screening donors for SCT and their subsequent exclusion from the blood donor pool may reduce the risk of leukofiltration failure. In addition, a study in a murine model found that SCT blood is associated with accelerated clearance in the recipient.8-11
SCD is highly prevalent in Saudi Arabia. The national premarital screening program conducted over a 6-year period, including 1,572,140 men and women, estimated the prevalence of SCD to be 0.26%, and SCT to be 4.2%.12 These figures are thought to be an underestimation, given the selective nature of the adult population included in this survey. Newborn screening in the Eastern Province of Saudi Arabia showed a prevalence of 21% for SCT and 2.6% for SCD.13 Because individuals with SCT are typically asymptomatic and are commonly identified only by proactive testing, they may be included in the regular blood donor pool.14
Given the prevalence of the sickle cell gene in the Saudi population, screening donors or blood units for HbS is pivotal for establishing a safe blood repository for patients with SCD. There are multiple techniques that could be used for testing for HbS, including turbidity tests, point-of-care (POC) testing using various principles, and hemoglobin electrophoresis. Among all of these techniques, turbidity tests are commonly used for screening RBC units before issuing to patients with SCD or for intrauterine transfusion.
The Sickle SCAN (Biomedomics, Inc.) test is a POC testing technology that relies on a lateral flow immunoassay using polyclonal antibodies against human HbS, HbC, and HbA for qualitative assessment of these hemoglobin types. In this pilot study, we evaluate the sensitivity and specificity of Sickle SCAN for detecting HbS in blood donors and blood units in Jeddah, Saudi Arabia.
MATERIALS AND METHODS
This pilot study was conducted at King Abdulaziz University Hospital (KAUH) in Jeddah, Saudi Arabia, following approval by the hospital ethical committee.
Blood donors
Donors were approached sequentially in the blood donation area at KAUH between July 24, 2016, and August 8, 2016. All donors fulfilled eligibility criteria for whole blood donation based on AABB Standards for Blood Banks and Transfusion Services (30th edition). Eligible donors were approached by a study team member to obtain consent. After obtaining an informed consent, the following data were collected from participants: date of birth, previous history of anemia, and family history of anemia.
After following standard procedure for collection of whole blood, a 4 mL sample was obtained from the diversion pouch in ethylenediaminetetraacetic acid tubes (BD Vacutainer K3 EDTA, Becton, Dickinson, and Co.) and stored at 4°C. Sickle SCAN was used to test these samples on a daily basis. The procedure was performed according to the manufacturer's instruction.15 The capillary sampler provided with the Sickle SCAN kit was used to obtain 5 μL from the venous blood sample in the ethylenediaminetetraacetic acid tube and transfer it to the provided buffer to release hemoglobin by lysing RBCs. Five drops of the treated sample were then added to the sample inlet of the Sickle SCAN cartridge. The result was read after 5 minutes (Fig. 1).
The remaining sample in the ethylenediaminetetraacetic acid tube was used for complete blood count with use of an automated hematology analyzer (XN-9000, Sysmex) and capillary electrophoresis with use of a liquid flow electrophoresis instrument (Capillarys 2, Sebia).
Blood units
Blood units collected from all donors were processed as per routine procedure. We then traced blood units from donors who were identified by hemoglobin electrophoresis as containing HbS, in addition to a number of blood units from donors who had normal hemoglobin capillary electrophoresis (HEP). Blood from these units' segments was then tested using Sickle SCAN.
Patients with SCD
Known patients with SCD receiving care at KAUH between July 2016 and September 2016, were approached sequentially to participate in this study. Control individuals from among family members were also approached sequentially for enrollment. After an informed consent was signed, 4 mL of blood were collected in ethylenediaminetetraacetic acid tubes, and samples were stored at 4°C. Samples were then tested using Sickle SCAN kits, and HEP was performed using the Sebia Capillarys 2 instrument.
RESULTS
Blood donors
Two hundred blood donors were enrolled: 191 males and nine females. All approached individuals agreed to participate and gave consent. Mean age at enrollment was 30 years (±9.3). One-half of the donors were Saudi nationals (99; 49.5%) These demographics were representative of the general blood donor pool at KAUH.16 The low number of female donors is a recognized phenomenon across the country.17
Medical history
One hundred ninety-six participants had no past history of anemia, and 199 had no previous diagnosis of SCT and no family history of SCD in a first-degree relative.
Donor laboratory values
At enrollment, the mean hemoglobin assessed on CBC was 15.7 g/dL (range, 12.2-17), and mean hemoglobin assessed by POC hemoglobin check was 14.9 g/dL (range, 12.5-17).
Sickle cell screening
When tested by the Sickle SCAN POC test, there were five participants with SCT, and the rest had only HbA (Table 1). With use of the gold standard, HEP, five participants had SCT (HbAS), three had β-thalassemia trait, had three had other phenotypes (Table 1). In this donor population, the Sickle SCAN test diagnosed SCT with 100% sensitivity and 100% specificity.
| Results by Sickle SCAN | Total | |||
|---|---|---|---|---|
| AS | Hb AA | |||
| Results by capillary hemoglobin electrophoresis | HbAS | 5 | 5 | |
| β-thalassemia trait (AF) | 4 | 3 | ||
| HbAD | 1 | 1 | ||
| HbAE | 1 | 1 | ||
| HbAA | 189 | 189 | ||
| Total | 5 | 195 | 200 | |
Blood units
Thirteen RBC bags were tested using the Sickle SCAN kit, including five donations that were diagnosed with SCT (HbAS), and eight donations with normal hemoglobin (HbAA). Sickle SCAN results were in agreement with HEP test results in 13 of 13 samples.
Patients
Fifty-seven patients with known SCD and their immediate family members were approached sequentially in the hematology clinic and daycare unit. All individuals who were approached agreed and consented to participate. Mean age was 24.1 years (±10.3), and 26 (45.6%) were males. Thirty-two (56.1%) of the patients were Saudi nationals.
Patient laboratory values
Mean hemoglobin at enrollment was 8.7 g/dL (range, 4.2-15). All patients and family members were previously tested and diagnosed by HEP. Twenty-one patients had homozygous SCD (HbSS), eight patients were double heterozygous for HbS and β-thalassemia (HbSβ), one had β-thalassemia trait, 24 had SCT (HbAS), and one was unaffected (HbAA).
Patient testing
One patient was missing recent HEP test results and was excluded from analysis. All patients (21/21) known to have homozygous SCD (HbSS) by HEP were identified by Sickle SCAN testing. All 24 individuals with SCT (HbAS) previously tested by HEP were confirmed to have SCT by Sickle SCAN. Seven patients identified as double heterozygous for HbS and HbSβ by HEP were classified as homozygous sickle cell (HbSS), and one as SCT (HbAS) by Sickle SCAN (Table 2).
| Results by Sickle SCAN | |||||
|---|---|---|---|---|---|
| SS | AS | Hb AA | Total | ||
| Results by capillary hemoglobin electrophoresis | HbSS | 21 | 21 | ||
| HbAS | 24 | 24 | |||
| HbSβ | 7 | 1 | 8 | ||
| β-thalassemia trait | 1 | 1 | |||
| HbSD | 1 | 1 | |||
| HbAA | 1 | 1 | |||
| Total | 28 | 26 | 2 | 56* | |
- * One patient was missing recent test results and was excluded.
Sickle SCAN testing showed 100% sensitivity and 100% specificity for diagnosis of homozygous SCD (HbSS) and SCT (HbAS).
DISCUSSION
In 2015, Kanter et al18 reported a high diagnostic accuracy of Sickle SCAN, a novel POC test that relies on lateral flow technology with remarkable sensitivity and specificity for detection of HbS and HbC.19 Both sensitivity and specificity for diagnosis of HbSS, HbAS, HbSC, HbAC, and HbAA were 99%. In a recent study of the Sickle SCAN in 250 patient samples, including 143 adults and 107 newborns, the test showed high accuracy in identifying phenotypes AS, AC, SS/SB, and SC.20
In this pilot study, we found the Sickle SCAN test to have a 100% sensitivity and specificity in detecting SCT in blood donors in Jeddah, Saudi Arabia. The test identified five of 200 donors who had SCT, which was confirmed by the gold standard test, HEP. RBC units from donors with SCT were correctly identified by Sickle SCAN.
Furthermore, the test was 100% sensitive and specific for identifying 21 of 21 patients with known SCD. It also showed a 100% sensitivity and specificity for diagnosing SCT in family members of patients with SCD.
Despite development of a number of POC testing methods for the presence of HbS,21 there have been no published comparisons for testing blood donors or RBC units. Sickle turbidity tests, such as an HbS solubility test kit (SICKLEDEX, Streck Inc.) have been routinely used for this purpose. It may be the most cost-effective way to screen for the presence of HbS at the current time. However, when compared with other POC testing methods, SICKLEDEX has some limitations.22 SICKLEDEX requires bringing the reagents from refrigerated temperature to room temperature before testing can be performed; then, an incubation period of 6 to 15 minutes is required before reading. For samples with low hematocrit, centrifugation of the sample for 5 to 10 minutes is necessary before performing SICKLEDEX. On the other hand, Sickle SCAN can be read after 2 to 5 minutes, without the need to refrigerate the reagents. A different POC testing device (HemoTypeSC, Silver Lake Research Corp.) can also be performed with reagents at ambient temperature, but results are only available after 10 minutes.21 New POC tests also have the advantage of differentiating between SCD and SCT, which is not feasible using SICKLEDEX. None of the POC testing methods offer the possibility of automation. Using them for screening individual units before issuing to specific patients (patients with SCD or patients receiving intrauterine transfusion) may be a reasonable approach. Whether blood suppliers at countries with high prevalence of SCT will need to consider universal donor screening for HbS is unclear, but high-throughput automated methods such as HEP and high-performance liquid chromatography may be best suited for this purpose.
The findings of this pilot project suggest that POC testing could be a reasonable option for screening donors for the presence of HbS at presentation for initial evaluation. Available evidence has proven it to be an accurate POC test for SCD,18, 20, 23 with test failure only rarely reported in extreme weather conditions or high humidity.24 It requires minimal training and can be performed at the time of hemoglobin measurement for donor qualification.
Limitations of our study include the relatively small sample size. Larger-scale studies are required to confirm these findings and support use of this testing method for screening blood donors and blood units.
CONCLUSION
In Saudi Arabia, especially in areas of high prevalence of the HbS gene, there is a need for screening of blood donors and blood units for SCT to ensure the safety of transfusion for patients with SCD. Sickle SCAN has consistently showed accuracy and reliability as a POC screening method for HbS and it may well be a reliable alternative to sickle solubility testing in the setting of blood donation; however, further research is required to support our findings.
CONFLICT OF INTEREST
The authors have disclosed no conflicts of interest.
