The role of discriminant functions in screening for beta-thalassaemia traits during pregnancy.
BACKGROUND
The mean red cell volume (MCV) has been shown to be useful in a 2-stage screening process for beta-thalassaemia traits among pregnant women though associated with a large number of false positive results. We tested prospectively the ability of 5 discriminant functions (DF), (England & Fraser, Shine & Lal, Mentzer, Srivistava and Klee et al) to reduce the number of false positives when used as additional screening determinants for beta-thalassaemia in antenatal patients with red cell microcytosis.


METHODS
The diagnostic performance of each DF was compared in 493 patients with microcytosis and known beta-thalassaemia status. Truth table analysis and Receiver Operation Characteristic curves for each function were determined.


RESULTS
11.4% of the patients with microcytosis were diagnosed to have beta-thalassaemia traits. DFs incorporating the red cell indices: haemoglobin or total red cell count are unsuitable during pregnancy. Shine & Lal's index [(0.01 x MCH x (< MCV)2] reduced the number of people recalled for confirmatory testing by 31.1% and increased the diagnostic yield to 38.7% while maintaining a negative predictive value for the test of 0.993.


CONCLUSIONS
We conclude that a 3-stage screening process for beta-thalassaemia among pregnant women in Singapore involving the MCV, Shine & Lal's index and a confirmatory test to be both valid and cost-effective.
Yeo
G S
GS
Department of Maternal-Fetal Medicine, Kandang Kerbau Hospital, Singapore.
Tan
K H
KH
Liu
T C
TC
D003937:Diagnosis, Differential; D016002:Discriminant Analysis; D004909:Erythrocyte Indices; D005260:Female; D005820:Genetic Testing; D006801:Humans; D007231:Infant, Newborn; D008403:Mass Screening; D010375:Pedigree; D011237:Predictive Value of Tests; D011247:Pregnancy; D011250:Pregnancy Complications, Hematologic / Q000097:blood / Q000175:diagnosis / Q000517:prevention & control*; D011295:Prenatal Care; D012372:ROC Curve; D017086:beta-Thalassemia / Q000097:blood / Q000175:diagnosis / Q000235:genetics / Q000517:prevention & control*