Evaluation of a new screening test for sickle cell haemoglobin

Hemoglobin S identification in blood donors: A cross section of prevalence

Introduction

In Brazil, the sickle cell trait (SCT) has an average prevalence of 4% in the general population and 6–10% among Afro-descendants. Although SCT is highly prevalent, a large segment of the population ignores their status. The Therapeutic Guidelines prohibit the transfusion of SCT red blood cells into patients with hemoglobin disorders or severe acidosis and newborns.

Methods

This was a cross-sectional study with data from 37,310 blood donation candidates. The study included only eligible first-time donors qualified to be tested for the presence of hemoglobin S (HbS) at the Fundação Hemominas Juiz de Fora, Brazil. The variables studied were gender, skin color, age, type of donation, place of birth, blood type, result of the solubility test for hemoglobin S (HbST) and hemoglobin electrophoresis (HbEF). Statistical analysis was performed using the Q square test and the Kappa index of agreement for comparing biochemical methods. This project was approved by the National Research Ethics Committee.

Results

The analysis of first-time donor data showed that 7166 were considered eligible. A total of 127 of the 7166 donors were carriers of SCT (1.77%). Among the blood donors, 73.23% were from the local area. The HbST and HbEF were found to be 100% in concordance. Sensitivity was not tested in the present study.

Conclusions

The HbST is highly specific for identifying the HbS, but sensitivity was not tested in this study. The screening of blood donors for abnormal hemoglobins is useful, helping to detect and counsel heterozygous people. The study seeks to identify the prevalence of SCT in a region of Brazil.

Evaluation of the particle gel diffusion technique for the detection of haemoglobin S in Sudanese patients

BACKGROUND

Sickle cell disease is a heterogenous disorder characterized by an abnormal haemoglobin and sickling phenomena of red cells. It is prevalent among certain nomadic tribes in Sudan. Painful, aplastic and haemolytic crises mark sickle cell anaemia. Haemoglobin S (HbS) is detected using haemoglobin electrophoresis, iso-electric focusing and/or high-performance liquid chromatography techniques with high sensitivity, but entails cost and expertise. This study aimed to determine the sensitivity, specificity and positive predictive values (PPV) of the ID-particle gel diffusion technique for screening, diagnosis and phenotyping of HbS in patients with a provisional diagnosis of abnormal haemoglobin.

METHODS

Following informed consent, 100 sequential individuals who reported to a central referral haemoglobinopathy clinic were enrolled. ID-particle gel diffusion technique was compared with cellulose acetate electrophoresis to determine haemoglobin phenotypes.

RESULTS

The ID-particle gel test detected HbAA with 100% sensitivity and 100% specificity. Sensitivity for HbS was 100%, whether as HbSS or as a mixed pattern. HbSS was identified in all cases where this is the only haemoglobin present. Other patterns were detected with <100% specificity and these would require further testing by other means to definitively identify abnormal haemoglobins.

CONCLUSIONS

Although the ID-particle technique is a simple and cheap technique with high sensitivity, specificity and PPV compared with cellulose acetate electrophoresis in detecting HbSS, it could not differentiate HbAS from HbSS with high levels of HbF. High environmental temperatures could melt the test microtubes. Cellulose acetate electrophoresis remains the technique of choice for the screening of abnormal haemoglobins in the Sudan.

High pressure liquid chromatography and electrospray ionization mass spectrometry are advantageously integrated into a two-levels approach to detection and identification of haemoglobin variants

Detecting and correctly identifying haemoglobin (Hb) variants is typically achieved by a two-levels laboratory approach. We report our experience in dealing with 91 Hb variants, including a number of frequent and a few rare variants. Screening included akaline agarose gel electrophoresis (AGE), ion-exchange automated high-performance liquid chromatography (HPLC) and a test for deoxyhaemoglobin solubility. Identification was based on electrospray ionization-mass spectrometry (ESI-MS). Our results confirmed the advantages of HPLC over AGE for screening, because of the occurrence of some electrophoretically 'silent' variants. ESI-MS permitted the definitive identification of 90 of the 91 variants included in the study, in some cases (e.g. HbS) through the application of a simple protocol (direct injection of the sample), in other cases requiring the application of more demanding procedures (purification of the variant chain and peptide analysis after enzymatic or chemical cleavage). In an additional case (Hb J-Oxford), ESI-MS assay did not lead to definitive identification, but gave indications for designing the appropriate primers to focus DNA sequence analysis on the specific region of the gene. Deoxyhaemoglobin solubility test was positive only in the presence of HbS. We conclude that HPLC and ESI-MS are advantageously integrated into a two-level analytical system for the detection and confirmation of variant Hbs.