Hemoglobin A1c is frequently used in primary care to screen for and monitor disorders of glucose metabolism. A number of clinical syndromes may impact the accuracy of this laboratory value. This report describes a case of abnormally low hemoglobin A1c that was the result of an asymptomatic compound hemoglobinopathy (homozygous hemoglobin S disease and hereditary persistence of fetal hemoglobin) that had gone previously undiagnosed. Primary care physicians must be aware of such pitfalls in the use of this laboratory value and be prepared to use other values to monitor for and assess disorders of glucose metabolism.