Anemia Screening in Naval Aviation: Is Hemoglobin a Better Indicator Than Hematocrit as the Primary Index?

Because of the rigorous mental and physical health requirements for Naval Aviation, all applicants and designated personnel must meet physical standards, including initial and periodic screening for anemia. Most standards, including for accession to the U.S. Navy, use hemoglobin as the standard marker to screen for anemia. Moreover, previous literature generally supports the assertion that hemoglobin is more reliable and accurate than hematocrit. However, the U.S. Navy Aeromedical Reference and Waiver Guide uses a hematocrit standard for anemia screening. The purpose of this study was to determine whether hemoglobin or hematocrit correlates better with clinical anemia and evaluate which index is a more accurate indicator for anemia screening in Naval Aviation personnel.

This is a retrospective cross-sectional study of Naval Aviation applicants (N = 95) who were evaluated by the Human Performance and Aeromedical Qualifications department at Naval Aerospace Medical Institute Clinic in Pensacola, Florida, from January 1, 2015 to September 30, 2018. Data were collected from electronic medical records in a de-identified manner that included demographics, class designations, labs results, diagnoses, and final disposition. Logistic regression was used to analyze whether hemoglobin (using the U.S. Navy standard of 13.5 g/dL for men and 12.0 g/dL for women) or hematocrit (using the Naval Aviation standard of 40% for men and 37% for women) predicted the diagnosis of anemia for subjects having at least one lab sample (1-sample) and for those having three samples (3-samples). Sensitivity and specificity values were calculated for hemoglobin and hematocrit as tools to predict a diagnosis of anemia using the same standards in the 1-sample and 3-sample groups.

Data were collected for 95 subjects, 53 of whom had three sets of paired hemoglobin/hematocrit values. Using logistic regression, hemoglobin was found to be a statistically significant predictor of anemia for both the 1-sample group (odds ratio 3.4, confidence interval [1.130-10.196], P < 0.05) and the 3-sample group (odds ratio 10.5, confidence interval [1.776-62.580], P < 0.01). Hematocrit was not a significant predictor in either group. Hemoglobin was 80% sensitive and 52.3% specific for a diagnosis of anemia in the 1-sample group and 91.3% sensitive and 50.0% specific in the 3-samples group. Hematocrit was 86.7% sensitive and 35.4% specific for a diagnosis of anemia in the 1-sample group and 91.3% sensitive and 23.3% specific in the 3-samples group.

This study found that hemoglobin correlates better with the diagnosis of anemia than hematocrit. When three samples are analyzed, hemoglobin is equally sensitive and more specific than hematocrit. Based on these results and the U.S. Navy accession standards using hemoglobin as the standard index for anemia, the U.S. Navy Aeromedical Reference and Waiver Guide should consider using hemoglobin instead of hematocrit to screen for anemia. Future research should focus on prospective research to determine whether hemoglobin or hematocrit is a better indicator of anemia in screening military personnel.