Ethnicity questions and antenatal screening for sickle cell/thalassaemia [EQUANS] in England: a randomised controlled trial of two questionnaires

Abstract

Concepts allied to ethnicity are increasingly coming under question as legitimate variables for use in health research. A randomised controlled trial of two ethnicity screening questions for ascertaining risk of carrying genes associated with sickle cell and thalassaemia illustrates the challenges and limitations of assessing an association of social constructs and genetic statuses.

Objectives: To evaluate two candidate ethnicity screening questions in antenatal screening programmes in low, mixed and high sickle cell prevalence areas, and to identify time taken in administration of the questions by use of the following measures: (1) Proportions of respondents with missing ethnicity data and/or significant changes in ethnic/family origins upon re-interview. (2) Numbers of carriers of clinically significant haemoglobin disorders missed by ethnicity screening questions. (3) Time taken to explain screening question for sickle cell disease (SCD)/thalassaemia and obtain ethnic/family origins. (4) Proportion of clients providing usable ethnic/family origins data. (5) Reported ethnic/family origins in pregnant women at first booking with midwife.

Design: Ten-month (September 2002-June 2003) questionnaire study with random allocation to two self-administered ethnicity questions, comparison with laboratory results and results from re-interview. The settings were antenatal booking clinics in four geographical areas of England of varying expected foetal prevalence of SCD: very high (29.75 per 10,000 pregnancies); high (8.2); mixed high and low (1.29); and low (0.18). The subjects were 4,559 pregnant women at first booking with midwife.

Results: Proportions of respondents with missing ethnicity data and/or significant changes in ethnic/family origins upon re-interview were 4.33% (CI 2.63-6.68%) for a category-based question and 9.45% (CI 6.86-12.61%) for a binary plus open-ended question. Proportions of carriers missed were 5.74% (CI 2.34-11.46%) and 9.71% (CI 4.75-17.13%) by category-based and binary plus open-ended questions, respectively. Average time taken to ascertain ethnic/family origins for screening was between 2.17 and 5.12 minutes in different areas, and up to 15 minutes at the 95th centile. Usable ethnicity screening data was missing in 2.94% of instances. Errors in interpretation or missing data were 3.2% for a category-based question and 4.71% for a binary plus open-ended ethnicity question. Ethnicity Question A produces fewer cases of missing or misinterpreted data (p < 0.001).

Conclusions: A category-based ethnicity screening question was more effective than a binary plus open-ended question. Using the more effective question, 5.74% (CI 2.34-11.46%) of significant haemoglobinopathies will be missed in a selective screening programme, and 4.33% (CI 2.63-6.68%) of replies to an ethnicity screening question will be unreliable when compared to information given upon re-interview. In specific carefully circumscribed situations, namely, in antenatal screening for sickle cell and thalassaemia, it is possible to measure the degree of association between social constructs of ethnicity and health status in a manner that may help in effecting policy decisions.