Condition | Genotype | Neonatal screening* | By age 6 weeks | Older children (≥5 years), adolescents, and adults | ||||
Hb A (%) | Hb A2 (%) | Hb F (%) | Hb S (%) | Hb C (%) | ||||
Normal | AA | FA | FA or AF | 95 to 98 | 2 to 3 | <2 | 0 | 0 |
Beta thalassemia trait | A/(β0 or β+) | FA | FA | 90 to 95 | >3.5 (unless due to δβ; can be normal or lower) | 1 to 3 (significantly higher if due to δβ deletion) | 0 | 0 |
Sickle cell trait | AS | FAS | FAS | 50 to 60 | <3.5 | <2 | 35 to 45; may be lower if concomitant alpha thalassemia | 0 |
Homozygous sickle cell (Hb SS) disease | SS | FS | FS | 0 | <3.5 but may be increased with concomitant α-thalassemia. May be falsely elevated when measured by HPLC | 5 to 15; may be higher in rare cases | 85 to 95 | 0 |
Sickle-β0 thalassemia | Sβ0 | FS | FS | 0 | >3.5 but may be falsely elevated when measured by HPLC | 2 to 15 | 80 to 92 | 0 |
Sickle-β+ thalassemia | Sβ+ | FSA or FS¶ | FSA | 3 to 30 | >3.5 but may be falsely elevated when measured by HPLC | 2 to 10 | 65 to 90 | 0 |
Hb SC disease | SC | FSC | FSC | 0 | <3.5 | 1 to 5; may be higher in rare cases | 45 to 50 | 45 to 50 |
Hb CC diseaseΔ | CC | FC | FC | 0 | <3.5 | <2 | 0 | 95 |
Hb C traitΔ | AC | FAC | FAC | 50 to 60 | <3.5 | <2 | 0 | 40 to 50 |
Hb: hemoglobin; Hb A: adult hemoglobin; Hb F: fetal hemoglobin; δβ: delta-beta; HPLC: high-performance liquid chromatography; DNA: deoxyribonucleic acid.
* The neonatal screening patterns list the different hemoglobins in order of abundance. As an example, the FAS pattern has the greatest amount of Hb F, followed by Hb A, followed by Hb S.
¶ In sickle-β+ thalassemia, the quantity of Hb A at birth may be insufficient for detection.
Δ In Hb C trait, concomitant alpha thalassemia variants lower the percentage of Hb C, and Hb C levels <40% after iron deficiency is excluded or corrected may indicate a two-gene deletion at the alpha locus. Hb C trait plus a beta thalassemia variant could be misdiagnosed as Hb CC disease.Adapted from: Sickle cell disease in children and adolescents: Diagnosis, guidelines for comprehensive care, and care paths and protocols for management of acute and chronic complications. Revised at the Annual Meeting of the Sickle Cell Disease Care Consortium, Sedona, AZ, November 10-12, 2001.
With additional data from: Bain BJ. Sickle cell haemoglobin and its interactions with other variant haemoglobins and with thalassaemias. In: Haemoglobinopathy Diagnosis, 2nd ed, Wiley-Blackwell, Oxford, 2005.Do you want to add Medilib to your home screen?