Which condition would be coded as an additional diagnosis?

A. A hyponatremia (low sodium) laboratory finding that was documented by the physician and required treatment.
B. An abnormal electrocardiogram in a patient with untreated atrial fibrillation.
C. A headache in a patient who has acute sinusitis.
D. An abnormal hematocrit indicating a possible anemia not documented, treated, or worked up by the physician.