Safety spotlight: HbA1c testing in women with sickle cell trait

Laboratory tests for glycosylated haemoglobin (HbA1c) can underestimate past glycaemia in people with haemoglobin variants, such as those with sickle cell trait. This is because there is an increased red cell turnover in those with haemoglobin variants. This means that HbA1c tests, which estimate the glucose level over the preceding few weeks will be unreliable.

MNSI investigations identified that HbA1c tests were taken in mothers with sickle cell trait, when they were being tested for gestational diabetes. These tests were not processed by the laboratories, as the results of these tests are unreliable. There was no further evaluation of the diabetes risk in these mothers. National Institute for Health and Care Excellence (NICE) does not recommend HbA1c as a test for gestational diabetes in pregnancy, instead recommending a 2-hour oral glucose tolerance test. The HbA1c test may be used to assess women with pre-existing diabetes, to assess the level of risk for the pregnancy (NICE, 2015).

• How does your trust ensure that staff are aware that HbA1c testing is not reliable in mothers with haemoglobin variants including sickle cell trait?
• How does local guidance support staff to ensure there is further evaluation of diabetes in mothers with haemoglobin variants when considering HbA1c testing, as the result may underestimate past glycaemia?
• Is there a process in your trust for following up mothers who have samples rejected by the laboratory due to haemoglobin variants, so that an alternative method of testing for measurement of long-term sugar control is offered?