Approximately 25% of Ontario's 11.5 million population belong to ethnic groups at high risk for a- or β-thalassemia (thai) or sickle mutations. Although, in the past decade, 400 couples at risk for conceiving fetuses with devastating diseases caused by homozygosity or compound heterozygosity of these mutations elected to undergo DNAbased prenatal diagnosis, up to 80% remained undiagnosed and were not provided genetic counseling. To improve care, the Ontario Medical Association recently revised the Antenatal Record Form to include parents' ethnic background, maternal Hb and MCV, and to prompt laboratory hemoglobinopathy (HbX) investigation when indicated. Proficiency testing of HbX investigations revealed difficulties with the diagnosis of a°-thal trait, Hb H disease, and β-thal trait. (Table). Diagnosis % Missed Year rf'-thal trail 16 1994 a"-thal trait in conjunction with β-thal trait 85 1999 Hb H disease 29. 25 & 13 1992, 1993. 1996 β-lhal trait with borderline Hb A, level of 3.9% 20 & 23 1997,1998 Missed diagnosis of a°-thal trait was attributed to poor test sensitivity. Error rates for Hb H disease were traced to electrophoretic methods that failed to detect Hb H. β-thal trait errors were attributed to inaccuracy of Hb A, methods utilizing densitometry scanning. An April 2000 laboratory survey indicated that proper testing occurs to detect sickling mutations, but revealed potential deficiencies to detect a- and β-thal trait. Those were: inability to determine if a HbX investigation is for genetic counseling (88%); lack of definitive interpretive and referral mechanisms when results suggest the likelihood of fxthal trait (96%); omission of ferritin determination in microcytosis (60%); omission of a repeat exhaustive Hb H inclusion body search when a-thal trait is likely (36%); use of densitometry scanning for Hb A, quantitation (36%); lack of an appropriate method to determine elevated Hb F (44%); omission of Hb H inclusion body investigation in microcytic patients (12%); and use of an inappropriate stain for Hb H inclusion body investigation (24%). These deficiencies underscore the urgent need to draft Ontario laboratory practice guidelines. Review of HbX laboratory testing and interpretive practices is advised in other jurisdictions.