Interpret the following results (all tests performed manually) on an adult female named Mary Jones

RBC: 3.22 x 1012/L
Hemoglobin: 16.0 g/dL
Hematocrit: 30.0%

a. All are normal.
b. All are decreased.
c. Hemoglobin is elevated and other two are normal.
d. Values do not agree with the "rule of three."

ANS: D
The rule of three suggests that the hematocrit (3 x hemoglobin). For this example, the hematocrit (3 x 16.0) 48 30.0. Therefore one of the values has to be invalid unless the red cell morphology is abnormal. However, in this instance no red cell morphology supports these results (mean cell hemoglobin concentration [MCHC] = 16/30 ´ 100 = 53 g/dL, which is impossible). Note: An expansion of the rule of three states that the hematocrit 9 x RBC count 9 x 3.22 27%. In this case, some agreement exists between the two values. Thus just from the information given in this question, it appears that the incorrect value is the hemoglobin.