The genetic disorder where the hemoglobin shape changes to sickle shape due to oxygen holding capacity is called Sickle cell anemia. Hemoglobin S causes Sickle cell anemia. Parental testing detects the presence of this hemoglobin S, the red blood cells count, checking of more than one hemoglobin gene or abnormal hemoglobin The presence of hemoglobin S is identified.
This complicated process has over 900 variants, so hemoglobin S presence and count too are very important to be detected. The screening procedures which constitute the prenatal testing for sickle cell anemia are as follows:
Sodium Metabisulfite and Hemoglobin S Solubility Test;
here a blood sample is taken and few chemicals are added which has the tendency to reduce oxygen levels. The result is positive and that the person has a sickle cell trait then for sure hemoglobin S is present. The reduced oxygen levels produce abnormal sickle cells.
The Final Screening include the below tests;
Hemoglobinopathy (Hb) Evaluation; the hemoglobin types are usually varied thus the relative amounts of them are evaluated. The series of tests the Hb evaluation method has the capability to identify that particular variant. The methods are

•  Hemoglobin
  Electrophoresis.
•  Hemoglobin Fractionation.
•  Isoelectric Focusing
•  DNA Analysis.