The pH, conductivity and osmolality of low ionic strength solutions used within the U.K. for the antiglobulin test

Mean corpuscular volume/mean corpuscular hemoglobin values are not reliable predictors of the β-thalassemia carrier status among healthy diverse populations of Himachal Pradesh, India

BACKGROUND:

Himachal Pradesh is a hill state in North India in the Western Himalayas. β-thalassemia is a genetic disorder of hemoglobin inherited in an autosomal recessive manner that results in defective globin production leading to the early destruction of red blood cells. β-thalassemia has long been neglected in Himachal Pradesh due to popular belief that it runs along “Lahore-Gujarat-Punjab” belt in India. Therefore, there is no β-thalassemia testing facility currently in the state.

METHODS:

To estimate the prevalence of β-thalassemia carriers, we calculated the sample size based on probability proportional to size self-weighing design. In each of 20 selected colleges, 111 students having an age of 18–25 were tested for high-performance liquid chromatography (HPLC) and complete blood count. Some were further tested for the mutations. We computed sensitivity, specificity, positive predictive value (PPV) and negative predictive value, and receiver operating characteristic curve for mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) red cell parameters.

RESULTS:

Of the 2220 students, 57 were found to be β-thalassemia carrier by HPLC. The overall prevalence rate was 2.6% which translates to probable 180,000 β-thalassemia carriers in Himachal Pradesh. Six districts bordering highly endemic Punjab had a higher prevalence. Hemoglobin D-Punjab, Heterozygous-Iran Trait, and raised fetal hemoglobin were found. Thalassemia major and sickle cell disease were not found. Anemic status or MCV/MCH parameters were not found to be reliable predictors of thalassemia carrier status among the healthy populations of HP. The predominant mutation found was IVS 1–5 G > C.

CONCLUSION:

Popular ongoing strategy for screening with MCV and MCH has low-PPV and can miss upto 37% of true thalassemia carriers. HPLC is better strategy for screening carriers and reduces further spread of thalassemia.

Comparison of low ionic diluents for use with the Diamed antiglobulin gel test

Microtube column systems, although widely used in transfusion serology for the detection of red cell antibodies, may not detect weak Fy(a), Jk(a), S and K antibodies. A number of low ionic diluents are used to shorten the incubation time required for red cell antibody detection in the antiglobulin test. However, there are no published reports to show whether these low ionic diluents vary in their ability to detect red cell antibodies using microcolumn detection systems. Three low ionic diluents, Diamed ID-CellStab, Diamed ID-Diluent2 and an in-house produced low ionic strength solution (LISS), were assessed using the Diamed-ID LISS/Coombs microtube column system (in accordance with the manufacturer's instructions), to ascertain whether the choice of diluent influences red cell antibody detection. Two hundred and seventy patient samples were screened for red cell antibodies. The reaction strength was increased in 50% of the samples with detectable red cell antibodies using LISS as the diluent compared with ID-CellStab. Of the 51 red cell antibodies directed against Rhesus, Duffy, Kidd or Kell antigens, 21% reacted more strongly in LISS compared with Diamed ID-CellStab with a difference in grading of > or =1. Minimal disparity was found between ID-Diluent2 and LISS. Biochemical analysis of pH, osmolality, sodium, potassium and phosphate were comparable for ID-CellStab, ID-Diluent2 and LISS. Measurement of conductivity in each low ionic diluent was performed as a measure of ionic strength in the final reactant mix, as the same amount of low ionic diluent was used for each test. The conductivity was 3 x 5 mS cm for LISS and ID-Diluent2, and 5 x 8 mS cm for ID-CellStab; the acceptable range being 3 x 7 +/- 0 x 3 mS cm as cited in the Guidelines for the Blood Transfusion Services in the United Kingdom. This evaluation suggests that ID-CellStab is a suboptimal low ionic diluent for red cell antibody detection using Diamed-ID LISS/Coombs gel cards. The poorer performance of ID-CellStab compared with LISS may be explained by its higher ionic strength.