BACKGROUND/AIM Diabetes mellitus is a chronic disease that can affect the eye. Most diabetics are unaware they have retinopathy in the early stages of the disease but become symptomatic as the disease advances. The early detection and treatment of diabetic retinopathy are important. The aim of the study was to determine the positive predictive value of TAG test in detecting macular edema among the diabetics in the diabetic clinic of Enugu State University of Science and Technology Teaching Hospital Parklane (ESUTTHP), Enugu using the findings on clinical evaluation and OCT as the reference standard. This would help determine the reliability of TAG as a screening tool for diabetic macular edema. METHODS This was a hospital-based observational case-control study involving 124 patients attending the diabetic clinic of ESUTTHP. The cases were patients that had diabetic macular edema that was diagnosed using macular OCT while the controls were those that did not have it. The cases and controls were matched by sex and age in the ratio of 1:1. The patients had initial direct fundoscopy to identify those who were likely to have signs of diabetic macular edema and those who may not have it. They were then examined using TAG test followed by dilated fundoscopy with slit lamp bio-microscope and +78D lens. They then performed macular OCT scan. The initial fundoscopy and TAG test were done by research assistants while the principal researcher performed the dilated fundoscopy with slit lamp and +78D lens. The research assistants and principal researcher were blinded to the results of the initial fundoscopy and TAG test so as to reduce bias. RESULT A total of 124 consecutive patients were recruited during the study. Forty (32.3%) patients were males, while 84(67.7%) were females (M: F = 1:2.1). The age range of the study population was 42-80 years and the mean age was 60.50 ±8.51 years. The age range of the cases was 43-78 years while their mean age was 60.68 ±8.53 years. The age range for the controls was 42-80 years while their mean age was 60.32 ±8.54 years. Fifty-three (85.5%) of cases had a formal education and 46(74.2%) lived in an urban area. Sixty-one (98.4%) of the cases had type 2 diabetes mellitus. Fifty-four (87.1%) of the controls had a formal education and 52(83.9%) lived in an urban area. All the controls had type 2 diabetes mellitus. None of the socio-demographic variables among the cases and controls was statistically significant. The mean central foveal thickness of the cases was 238.01 ±84.46μm while the mean central foveal thickness of the controls was 200.58 ±16.86μm. The prevalence of diabetic macular edema among the diabetics on clinical examination was 50%. The sensitivity of TAG test in diagnosing diabetic macular edema among the cases was 74.2%, while its specificity was 58.1%. TAG test had a false negative rate of 25.8% while it had a false positive rate of 41.9%. The positive predictive value of TAG test in detecting macular edema among the diabetics was 63.9%.