AbstractObjectiveSouth Africa has a high burden of HIV infection and anaemia. These conditions may cause HbA_1c to over‐ or underestimate glycaemia; however, this has not been comprehensively investigated in African populations. We assessed the association of anaemia, HIV infection and antiretroviral therapy (ART) with HbA_1c, and implications for the detection and diagnosis of diabetes, in a black South African population.Research design and methodsIn this population‐based cross‐sectional study in eThekwini municipality (Durban), South Africa, we assessed HbA_1c and conducted oral glucose tolerance tests (OGTTs), HIV diagnostic tests and full blood count measurements among 1067 participants without a history of diabetes diagnosis. Linear regression was used to examine differences in HbA_1c by anaemia (comparator: no anaemia), or HIV and ART (comparator: no HIV) status. HbA_1c‐based diabetes prevalence was compared with OGTT‐based prevalence among individuals with anaemia and with untreated and ART‐treated HIV.ResultsIn adjusted analyses, normocytic and microcytic anaemia were associated with higher HbA_1c compared with no anaemia, whereas macrocytic anaemia and ART‐treated HIV were associated with lower HbA_1c compared with no anaemia and no HIV, respectively. However, magnitudes of association were small (range: = −3.4 mmol/mol or −0.31%, p < 0.001 [macrocytic anaemia] to = 2.1 mmol/mol or 0.19%, p < 0.001 [microcytic anaemia]). There was no significant difference in diabetes prevalence based on HbA_1c or OGTT among individuals with anaemia (2.9% vs. 3.3%, p = 0.69), untreated HIV (1.6% vs. 1.6% p = 1.00) or ART‐treated HIV (2.9% vs. 1.2%, p = 0.08).ConclusionsOur results suggest that anaemia and HIV status appear unlikely to materially affect the utility of HbA_1c for diabetes detection and diagnosis in this population. Further studies are needed to examine these associations in sub‐Saharan African populations.