ANC by the Duffy phenotype in Black patients who presented for a routine primary care visit. The shaded area represents the reference range for ANC at the institution where the blood work was obtained, with the dashed line indicating the reference median. Duffy-null refers to the Fy(a−b−) phenotype, and Duffy non-null indicates Fy(a−b+), Fy(a+b−), or Fy(a+b+) phenotypes, as determined serologically. Dots show individual ANC values, whereas the box represents median ANC and interquartile range. There is a statistically significant difference in ANC between the Duffy non-null (n = 40) and the Duffy-null (n = 80) individuals (P < .001). There is no statistically significant difference between the Duffy non-null ANC median and the reference median (P = .64), but there is a significant difference between the Duffy-null ANC median and the reference median (P < .001).