Strategics | Studies, Essays, Thesises » Anemia Screening in Naval Aviation, Is Hemoglobin a Better Indicator Than Hematocrit as the Primary Index

MILITARY MEDICINE, 185, 3/4:461, 2020 Anemia Screening in Naval Aviation: Is Hemoglobin a Better Indicator Than Hematocrit as the Primary Index? CDR William B. Nguyen, MD, MC, USN*; ENS Jacob M. Wyse, BA, MC, USN†; Sabrina M. Drollinger, MA*; LCDR Kai Cheng, MD, MC, USN Materials and Methods 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 135 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. Results 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 [1130–10196], P < 005) and the 3-sample group (odds ratio 105, confidence interval [1.776–62580], P < 001) 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 913% sensitive and 500% specific in the 3samples group Hematocrit was 867% sensitive and 354% specific for a diagnosis of anemia in the 1-sample group

and 91.3% sensitive and 233% specific in the 3-samples group Conclusions 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 US 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. INTRODUCTION Exceptional health standards are essential to safe and effective military aviation due to the rigorous mental and physi* Naval Aerospace Medical Institute, 340 Hulse Road, Pensacola, FL 32508 † F. Edward Hébert School of Medicine, Uniformed Services University, 4301 Jones Bridge Road, Bethesda, MD 20814 The

views expressed are solely those of the authors and do not reflect the official policy or position of the U.S Navy, the Department of Defense, or the U.S Government doi:10.1093/milmed/usz243 Published by Oxford University Press on behalf of the Association of Military Surgeons of the United States 2019. This work is written by (a) US Government employee(s) and is in the public domain in the US. MILITARY MEDICINE, Vol. 185, March/April 2020 cal demands placed on this specialized population.1 Consequently, each branch of the US military has its own mental and physical standards that applicants and designated (ie, trained and qualified) personnel must meet and maintain. The aviation physical standards for the U.S Navy are based on Chapter 15 of the Manual of the Medical Department U.S Navy NAVMED P-117, or MANMED,2 with further guidance and amplification from the U.S Navy Aeromedical Reference and Waiver Guide, or ARWG.3 These standards are more rigorous than those that apply to general

military personnel to ensure a high-sensitivity screening process that includes evaluation on multiple health conditions to minimize risks and maximize performance.3 Anemia screening is of particular 461 Downloaded from https://academic.oupcom/milmed/article/185/3-4/461/5607588 by guest on 27 March 2021 ABSTRACT Introduction 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 US 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. Anemia Screening in Naval Aviation 462 why Hct is a less reliable index than Hb in patients without thalassemia, as differences in the size of RBCs because of these factors are expected to affect the calculated Hct even though they do not affect the oxygen-carrying capacity of blood. Anemia affects 1.62 billion people worldwide and 3 million Americans.16 Although it would be reasonable to assume that the prevalence of anemia would be lower in a generally young and healthy military population, a 2016 study of 18,827 U.S Air Force basic trainees found a prevalence of anemia (defined by Hb < 13.5 g/dL for men and <120 g/dL for women) of 12.6% overall (89% for men and 254% for women).17 Anemia decreases the oxygen-carrying capacity of blood, which impairs oxygen delivery and compromises physical and mental performance. Young and healthy subjects may compensate for

anemia and remain asymptomatic under normal circumstances, but physical exertion and hypoxia as experienced during flight can overwhelm the body’s compensatory mechanisms. Consequently, anemia is considered disqualifying (CD) for military service,18 service in the Navy,2 and Naval Aviation specifically.3 However, the current method used during Naval Aviation screening is outdated and is not consistent with the current literature as the most effective means of identifying anemia. U.S Navy Guidelines for Anemia Screening The World Health Organization standards for anemia are Hb < 12 g/dL for females and <13 g/dL for males,16 whereas other sources cite different cutoffs depending on the sample population and the desired sensitivity and specificity of the test.5 In Article 15-54 of MANMED, the Navy defines anemia as Hb < 13.5 g/dL for males and <12 g/dL for females2 Accession to the Navy with Hb falling under this standard, which is stricter than the World Health

Organization definition, requires a waiver for anemia. The higher standards are deemed necessary because of the greater physical and mental stress that service in the Navy places on individuals compared with other work environments. Currently, the U.S Navy ARWG uses Hct level to screen for anemia in Naval Aviation applicants and designated personnel. The acceptable Hct values are 40% to 52% for males and 37% to 47% for females. If the initial level is below this standard, two additional Hct samples must be drawn; Hct is considered to meet standards if the average of three samples falls within normal range. If the average Hct falls outside the range above but is between 38.0% and 399% for males or 35.0% to 369% for females, history, physical exam, complete blood count (CBC) (including RBC count, RBC indices, manual differential, RBC morphology, and reticulocyte count), iron studies (including serum iron, serum ferritin, and total iron binding capacity (TIBC)), blood chemistry, liver

function tests, and TSH should be performed.3 If this workup is normal, the condition is not considered disqualifying (NCD), and a waiver is not required. If the workup is MILITARY MEDICINE, Vol. 185, March/April 2020 Downloaded from https://academic.oupcom/milmed/article/185/3-4/461/5607588 by guest on 27 March 2021 importance as it is a common condition and a potential risk to aviation safety. Generally, anemia is defined as a decrease in red blood cell (RBC) mass and, therefore, a decrease in the oxygencarrying capacity of the blood.4 Anemia may be caused by an insufficient number of RBCs or by a decrease in the amount of hemoglobin (Hb), the oxygen-carrying metalloprotein, in the RBCs.5 Clinically, anemia is diagnosed by laboratory values below a minimum cutoff in either of two red cell indices, either Hb or hematocrit (Hct).6 The concentration of Hb in RBCs is measured in grams per deciliter, whereas Hct represents the volume fraction of the blood occupied by RBCs and is

expressed as a percentage.7 Both indices are affected by volume status, although it has less impact on Hb than on Hct.8 Historically, Hb was estimated by comparing the color of a sample of blood with a colorimetric reference, whereas Hct was measured directly by examination of centrifuged blood.9 However, in the modern clinical laboratory, automated cell counters use spectrophotometry techniques to measure the concentration of Hb directly and calculate Hct from the number of RBCs and their mean volume.10 Since Hb is the principal protein inside RBCs and Hct is a measurement of total RBC volume, these two parameters are often considered equivalent for measuring the oxygencarrying capacity of blood and diagnosing anemia. Hb and Hct have been shown to behave as identical parameters in certain clinical scenarios.11,12 However, Graitcer et al in 1981 found in a large survey of 13,040 children that Hb and Hct were not comparable parameters. Hct cutoffs overdiagnosed anemia in 1% to 10% of

subjects with normal Hb and underdiagnosed anemia in 20% to 50% of subjects with low Hb.13 Although the study’s subjects were children while military personnel are all adults, this shows that Hb and Hct are nonequivalent in an otherwise healthy population. Abdulazeez and Muhibi, in a study of 1,390 children with and without comorbidities, also found Hb and Hct to differ significantly and additionally found Hb to be more sensitive than Hct in detecting anemia.14 Using a large sample of several hundred thousand patients, Keen8 found a greater variation in Hct than in Hb attributed to factors such as damage to RBCs during shipment because of time and temperature, hemodilution, and differences in equipment. The author concluded that Hb should be the primary index used for the clinical assessment and management of anemia,8 though the study looked at dialysis patients and thus may not be applicable to military personnel. In a more recent 2013 study, Insiripong et al. found a significantly

higher Hct/Hb ratio in subjects with alpha-thalassemia than in normal subjects and hypothesized that differences in density and hydration of RBCs, entrapment of plasma, nucleated RBCs, and WBC interference may explain this difference.15 This finding makes Hb more sensitive than Hct in screening for thalassemia, which is important for finding this disease in military personnel. Moreover, these hypotheses may help explain Anemia Screening in Naval Aviation Purpose of Study This literature review has shown discrepancy in the sensitivity and clinical accuracy of Hb and Hct as well as differences in the anemia screening guidelines and criteria used by the different military branches and civilian aviation. The purpose of this study was to determine whether Hb is a better indicator than Hct for anemia screening in Naval Aviation personnel. It was hypothesized that Hb is a better predictor of anemia than Hct. Because of the limited studies that directly addressed which one of these

indices is better for anemia screening, we hope to add to this body of work. Lastly, we plan to use the results of the current study to inform recommendations for change to the ARWG on anemia screening in Naval Aviation and to encourage standardization of anemia screening among military aviation communities. METHODS Ethical Statement The research protocol was approved for exemption from the Institutional Review Boards by the Clinical Investigation Department, Naval Medical Center Portsmouth, and the University of West Florida (IRB 2019-044). Research Design This is a retrospective cross-sectional study using electronic medical record review of aviation applicants found to have an Hct level below the established standard provided by the ARWG (<40% for male and <37% for female) during their initial CBC screening as part of their initial history and physical exam. Subsequent labs, final diagnoses and disposition, and demographics (age, gender, and race) for these individuals were

collected from electronic medical record databases (Composite Health Care System, Armed Forces Health Longitudinal Technology Application, and Aeromedical Electronic MILITARY MEDICINE, Vol. 185, March/April 2020 Resource Office) and combined with the indices from the initial screening. The class designations of the subjects were also collected: class 1: Student Naval Aviator; class 2: Student Naval Flight Officer, Student Naval Flight Surgeon, Air Crew Applicants, etc.; class 3/4: Members in aviation not requiring them to be physically airborne such as Air Traffic Controllers and Unmanned Aerial Vehicle applicants. The collected data were entered into a Microsoft Excel spreadsheet and were protected and de-identified. Study Population Study participants (N = 95) were Naval and Marine Aviation applicants who were evaluated by the Human Performance and Aeromedical Qualifications department at NAMI from January 1, 2015 to September 30, 2018. Data Analysis We used Microsoft Excel to

perform descriptive analysis of the collected data, including age, gender, race, aviation class, diagnosis, and aeromedical disposition. We used the Statistical Package for the Social Sciences (SPSS version 24.0) for Windows to perform binomial logistic regression on the data from the group of subjects with at least one paired set of Hb/Hct (1-sample) and from the group that had all three sets of labs (3-samples). The model used average Hb above or below the Navy MANMED cutoff (13.5 g/dL for men and 120 g/dL for women) and Hct above or below the Navy ARWG cutoff (40% for men and 37% for women) as independent variables and used any diagnosis of anemia as the dependent variable. This method was used to analyze whether average Hb or Hct below these cutoff values was predictive of a diagnosis of anemia. Clinical screening tests emphasize sensitivity and specificity; sensitivity represents the ability of a test to determine the presence of disease if it exists, whereas specificity

represents the ability of a test to accurately exclude disease if it does not exist.22 We used Microsoft Excel to obtain averages of the Hb and Hct values for each subject and calculate the sensitivity and specificity of Hb and Hct as screening tests for anemia. For calculations of sensitivity and specificity, mean Hb less than the MANMED cutoff and mean Hct less than the ARWG cutoff values were considered abnormal test results, and any diagnosis of anemia was used as the gold standard comparison test. A diagnosis of anemia was considered the gold standard because the diagnosis is the principal determinant of a service member’s aeromedical disposition and whether the member needs to apply for a waiver. RESULTS Sample Characteristics During the period January 1, 2015 to September 30, 2018, there were 100 applicants who met the inclusion criterion of 463 Downloaded from https://academic.oupcom/milmed/article/185/3-4/461/5607588 by guest on 27 March 2021 abnormal, the condition is

CD. However, the flight surgeon may apply for a waiver from the Naval Aerospace Medical Institute (NAMI). The waiver disposition outcomes include waiver recommended (WR) and waiver not recommended (WNR). If granted, a waiver allows the service member to serve in his or her position in Naval Aviation, with restrictions and re-evaluation as specified by the conditions of the waiver. Similar to the Navy’s ARWG, U.S Air Force Waiver Guide uses Hct to screen aviators for anemia,19 whereas the Army Flight Surgeon’s Aeromedical Checklist accepts either Hb or Hct level as a screening criterion.20 The civilian aviation community, overseen by the Federal Aviation Administration, uses Hb as the primary screening index. Federal Aviation Administration Aviators only need to have Hb above 10 g/dL in order to meet flying standards,21 as the physical and mental demands of civilian aviation are, in general, not as rigorous as military aviation. Anemia Screening in Naval Aviation having Hct

below the ARWG standard (40% for men and 37% for women). By the guidance of the ARWG, this finding requires additional investigation and lab work for anemia screening. Upon further review of the individual cases, five subjects who had no additional labs or workups as recommended by the ARWG were excluded. All anemia screening labs had paired Hct/Hb values. If the initial Hct is below standard, the ARWG recommends drawing two additional Hct lab samples and then calculating the average. However, depending on various factors including flight surgeon discretion, not all subjects had additional labs drawn. Of the 95 subjects eligible for the study, all had at least one paired set of Hb/Hct (1sample), 86 had at least two sets (2-samples), and 53 had all three sets (3-samples). Table I shows the demographic characteristics, diagnoses, and disposition of the study sample. The sample’s age range TABLE I. Demographic Characteristics, Diagnoses, and Dispositions of Study Population (N = 95) N

Percent Mean SD Female Male Both genders 24 61 95 35.8 64.2 100 23.3 26.5 24.9 3.26 8.46 7.28 Race N Percent Caucasian African American Asian Other/unknowna 70 17 4 4 73.7 17.9 4.2 4.2 Aviation Class Types N Percent Class 1b Class 2c Class 3d 26 46 23 27.4 48.4 24.2 Diagnoses N Percent No diagnosise 65 12 9 7 2 68.4 12.6 9.5 7.4 2.1 Iron deficiency anemia Unspecified anemia Thalassemia(s)f Othersg N Male (%) N Below Hb Standardh (%) N Below Hct Standardi (%) 61 (64.2) 19 (63.3) 5 (41.7) 7 (100) 55 (57.9) 24 (80.0) 8 (66.7) 7 (100) 68 (71.6) 26 (86.7) 10 (83.3) 7 (100) Final Disposition N Percent NCDj CDWRk CDWNRl CDWR/WNR for otherm 66 26 2 1 69.5 27.4 2.1 1.1 All subjects Any anemia Iron deficiency anemia Thalassemia(s) a American Indian (1), Middle Eastern (1), Hispanic (1), and unknown race (1). b Pilots. c Flight officers, flight surgeons, flight physiologist, flight physician assistants, air crew, etc. d Nonairborne aviation personnel such

as air traffic control, unmanned aircraft operators. e No diagnosis as determined by labs and/or medical providers. f Alpha (1), beta (4), thalassemia minor (2). g G6PD anemia (1) and other hemoglobinopathies (1) h Hb < 13.5 g/dL for men, <120 for women i Hct < 40% for men, <37% for women. j Not considered disqualifying. k Considered disqualifying, waiver recommended. l Considered disqualifying, waiver not recommended. m Given CDWR for anemia but WNR for another medical condition. 464 MILITARY MEDICINE, Vol. 185, March/April 2020 Downloaded from https://academic.oupcom/milmed/article/185/3-4/461/5607588 by guest on 27 March 2021 Age by Gender Anemia Screening in Naval Aviation Logistic Regression Analysis The logistic regression analysis of Hb and Hct in predicting the diagnosis of anemia is included in Table II. For the 1-sample average analysis, the model’s correlation was statistically significant (χ 2 (2) = 10.559, P < 0005), but only Hb below the

standard was a significant predictor of a diagnosis of anemia. For subjects with Hb below the standard in the 1-sample group, the odds of being diagnosed with anemia increase by a factor of 3.4 For the 3-samples analysis, the model’s correlation was also statistically significant (χ 2 (2) = 11.329, P < 0.003), and again, only Hb was a significant predictor of anemia. For subjects with Hb below the standard in the 3-samples group, the odds of being diagnosed with anemia increase by a factor of 10.5 Sensitivity and Specificity The sensitivity and specificity of Hb and Hct below the respective standards compared with the gold standard of an anemia diagnosis are presented in Table III for the 1-sample (N = 95) and the 3-samples (N = 53) groups. In the 1-sample data, Hct was slightly more sensitive than Hb, but in the 3-samples, the sensitivity was the same. Specificity was higher for Hb than Hct in both the 1-sample and the 3-samples data. DISCUSSION Because of the rigorous

physical and mental demands of Naval Aviation, it is important that all personnel meet the highest physical and mental standards to thrive in this demanding environment. Anemia is a disqualifying condition in Naval Aviation because of its negative impact on performance and safety. The data obtained in this study provide a better understanding of the use of Hb and Hct in the anemia screening process. The limited literature on whether Hb or Hct was a better indicator for anemia screening underscores the need for this study. MILITARY MEDICINE, Vol. 185, March/April 2020 TABLE II. Logistic Regression for 1-Sample (N = 95) and 3-Samples (N = 53) Average Hb and Hct in Predicting Anemia Diagnosis B SE df Exp(B) Hematocrit-1 0.711 0655 1 Hemoglobin-1∗ 1.222 0561 1 Constant∗∗∗ −2.116 0594 1 Hematocrit-3 −0.011 1062 1 Hemoglobin-3∗∗ 2.355 0909 1 Constant∗ −2.008 0977 1 2.035 3.394 0.120 0.989 10.542 0.134 95% CI for Exp(B) Lower Upper 0.563 1.130 7.352 10.196 0.123

1.776 7.930 62.580 Notes. Nagelkerke R2 = 0148 for 1-sample regression Nagelkerke R2 = 0.258 for 3-samples regression B, regression coefficients for each variable in the logistic regression; SE, standard error; df, degrees of freedom; Exp(B), OR associated with each variable, based on the exponent of B; CI, confidence intervals for the OR. ∗ P < 05; ∗∗ P < 01; ∗∗∗ P < 001 TABLE III. Sensitivity and Specificity for 1-Sample (N = 95) and 3-Samples (N = 53) Average Hb and Hct Hb-1a Hct-1a Hb-3b Hct-3b Sensitivity Specificity 80.0% 86.7% 91.3% 91.3% 52.3% 35.4% 50.0% 23.3% a At least one paired (Hb/Hct) sample. b All three paired (Hb/Hct) samples. We analyzed both the 1-sample (N = 95) and 3-samples (N = 53) data to determine whether Hb and/or Hct below established standard predicted a diagnosis of anemia. For the logistic regression models, Hb was a significant predictor of anemia diagnosis for both the 1-sample (odds ratio [OR] 3.4, confidence interval [CI,

1130–10196], P < 005) and 3-samples (OR 10.5, CI [1776–62580], P < 001), whereas Hct was not a statistically significant predictor in either sample. In the 1-sample calculation, Hct was slightly more sensitive than Hb (867%–800%), but Hb was more specific (52.3%–354%) in predicting the diagnoses of anemia For the 3-samples calculation, the sensitivity for Hct and Hb were identical at 91.3%, but Hb was more specific than Hct in diagnosing anemia (50%–23.3%) The 3-samples (N = 53) data follow the standard workup set forth by the ARWG and yield higher sensitivity and specificity for all tests; thus, we felt that it carried more weight toward our conclusions. Based on these findings, it is reasonable to conclude that Hb is a more reliable test than Hct for anemia screening in the study population. This finding is consistent with Graitcer et al., Keen, Insiripong et al., and Abdulazeez and Muhibi, who found Hb to be a more accurate indicator of anemia than Hct.8,13,14,15 Of

these studies, the study by Graitcer et al., which used over 13,000 same-patient Hb/Hct samples, most closely resembled our investigation, though that study was in children. Their 465 Downloaded from https://academic.oupcom/milmed/article/185/3-4/461/5607588 by guest on 27 March 2021 at the time of screening were between 18 and 66 years old (M = 24.9; SD = 73) The majority were male (642%), Caucasian (73.7%), and class 2 personnel (484%) The majority of the subjects received no diagnosis of anemia (684%) Table II shows characteristics of the Hb/Hct data for the cohort of 95 subjects and for subgroups including subjects with anemia and with the two most common diagnoses, iron deficiency anemia and thalassemias. All subjects who received no diagnosis of anemia received an aeromedical disposition of NCD, and one subject with a diagnosis of G6PD anemia also received a disposition of NCD. For all other subjects with a diagnosis of anemia, the disposition was CD For two subjects, both

with diagnoses of unspecified anemia, waivers were not recommended (CDWNR), and waivers for anemia were recommended (CDWR) for all remaining subjects. Anemia Screening in Naval Aviation Limitations This study, like other small retrospective studies, offers inferior evidence in comparison with larger studies or prospective studies. Retrospective studies provide associations and cannot establish causation or provide temporal relationship.23 Our study sample came from a pool of subjects who had Hct below the ARWG standard and required a workup for anemia based on existing ARWG guidelines. Thus, selection bias was a limitation of this study, as our sample captures subject with substandard Hct and normal Hb but misses patients with substandard Hb and normal Hct. This method potentially biases the results and limits this study’s ability to generalize our findings to the broader population of Naval Aviation personnel. Since our sample consists of Naval Aviation personnel, we must be

additionally cautious in generalizing our findings outside this population. Another limitation identified by Audet et al. of this type of research design is that retrospective chart reviews are limited by missing or inadequate documentation.24 There is a potential for sampling bias since our record review only had access to completed flight physicals, so it is possible that the sample missed physicals that were initiated and abandoned. Within the study sample, only 53 of the 95 subjects had three sets of labs drawn as required be the ARWG. This likely occurred due to medical personnel failing to enter the data or clinical decisions made by medical providers not to further pursue the recommended testing. In certain instances, even when labs were below standard with subsequent labs, those members did not receive the diagnosis of anemia and were cleared for training. There is significant potential for this missing data to have impacted our results. Recommendations Based on the literature

review and the findings of this study, we recommend a modification to the ARWG anemia screening to use a Hb standard to screen for anemia in aviation personnel. Based on our results, the current Navy MANMED 466 Hb standard of 13.5 g/dL for men and 120 g/dL for women, which is already used for general duty screening and accession to the Navy, has superior test characteristics than the current AWRG Hct standard. For patients with abnormal lab results, our results show that taking an average of three tests improves the sensitivity and specificity of both indices for diagnosing anemia. Another option would be to follow the US Army’s waiver guide, which uses either Hb or Hct as a marker for anemia.20 Additionally, there is wide variability of anemia screening criteria across the different military branches. We recommend standardizing guidelines across all branches to simplify identification of anemia and increase consistency of diagnosis. Future Research Our results could be more

rigorously examined using a larger and more inclusive retrospective study or using a prospective study design. A future researcher could use both Hb and Hct cutoffs for inclusion in the study with additional workup required if either Hb or Hct levels indicate anemia. This would provide additional evidence to determine the best method for identifying anemia in Naval Aviation personnel. It would also be helpful to investigate this research question in other military branches and to pool study samples across the services to improve the generalizability of the results. REFERENCES 1. Mansikka H, Simola P, Virtanen K, Harris D, Oksama L: Fighter pilots’ heart rate, heart rate variation and performance during instrument approaches. Ergonomics 2016; 59(10): 1344–52 2. Physical examinations and standards for enlistment, commission and special duty. In: Manual of the Medical Department, pp 15-1–15110 Falls Church, VA, US Navy Bureau of Medicine and Surgery, 2019:. Available at

https://wwwmednavymil/directives/Documents/ NAVMED P-117 (MANMED)/Chapter 15 Medical Examinations (incorporates Changes 126, 135–138, 140, 145, 150–152, 154–156, 160, 164–167).pdf 3. Naval Aerospace Medical Institute: US Navy Aeromedical Reference and Waiver Guide. November 27, 2018 Available at https://wwwmed navy.mil/sites/nmotc/nami/arwg/Documents/WaiverGuide/Complete Waiver Guide.pdf accessed on 06 July 2019 4. Northrop-Clewes CA, Thurnham DI: Biomarkers for the differentiation of anemia and their clinical usefulness. J Blood Med 2013; 4: 11–22 5. Beutler E, Waalen J: The definition of anemia: what is the lower limit of normal of the blood hemoglobin concentration? Blood 2006; 107(5): 1747–50. 6. Cascio MJ, Deloughery TG: Anemia: evaluation and diagnostic tests Med Clin North Am 2017; 101(2): 263–84. 7. Hayuanta HH: Can hemoglobin-hematocrit relationship be used to assess hydration status? Cermin Dunia Kedokteran 2016; 43(2): 139–42. 8. Keen ML: Hemoglobin and

hematocrit: an analysis of clinical accuracy Case study of the anemic patient ANNA J 1998; 25(1): 83–6. 9. Means RT: It all started in New Orleans: Wintrobe, the hematocrit and the definition of normal. Am J Med Sci 2011; 341(1): 64–5 10. Billett HH: Hemoglobin and hematocrit In: Clinical Methods: The History, Physical, and Laboratory Examinations, Ed 3rd. Edited by Walker HK, Hall WD, Hurst JW. Boston, MA, Butterworths, 1990 MILITARY MEDICINE, Vol. 185, March/April 2020 Downloaded from https://academic.oupcom/milmed/article/185/3-4/461/5607588 by guest on 27 March 2021 results indicated that 20% to 50% of patients who were considered normal using the Hct standard were considered anemic when Hb was used as the marker.13 The study by Insiripong et al. is also of particular importance to our research question, since that study found Hct to be less sensitive in detecting anemia in patients with alpha-thalassemia,15 a condition found in our study population that is important to

capture in screening aviation personnel. However, other studies, including a 2007 study of trauma patients by Nijboer et al. and a 2016 study of 100 day care children by Brunken et al., found Hb and Hct to behave as identical parameters11,12 Taken together, our findings are consistent with the limited research available for this topic. This study adds to the body of evidence that Hb is a more reliable standard than Hct in anemia screening and expands that evidence to a previously understudied population. Anemia Screening in Naval Aviation MILITARY MEDICINE, Vol. 185, March/April 2020 18. Office of the Under Secretary of Defense for Personnel and Readiness: Medical Standards for Appointment, Enlistment, or Induction into the Military Services. March 30, 2018 Available at https://wwwmednavy mil/sites/nmotc/nami/arwg/Documents/WaiverGuide/DODI 6130.03 JUL12.pdf accessed on 06 July 2019 19. US Air Force School of Aerospace Medicine: Air Force Waiver Guide October 5, 2017. Available

at https://wwwwpafbafmil/Portals/60/ documents/711/usafsam/USAFSAM-Wavier-Guide-171005.pdf accessed on 06 July 2019. 20. US Army Aeromedical Activity: Flight Surgeon’s Aeromedical Checklists. May 28, 2014 Available at http://glwachameddarmymil/ victoryclinic/documents/Army APLs 28may2014.pdf accessed on 06 July 2019. 21. Federal Aviation Administration: Guide for Aviation Medical Examiners March 27, 2019 Available at https://wwwfaagov/about/office org/ headquarters offices/avs/offices/aam/ame/guide/ accessed on 06 July 2019. 22. Lalkhen AG, McCluskey A: Clinical tests: sensitivity and specificity Continuing Education in Anaesthesia Critical Care & Pain 2008; 8(6): 221–3. 23. Nickson C: Retrospective studies and chart reviews Life in the Fast Lane. November 21, 2018 Available at https://lifeinthefastlanecom/ccc/ retrospective-studies-chart-reviews accessed on 06 July 2019. 24. Audet A-M, Goodnough LT, Parvin CA: Evaluating the appropriateness of red blood cell transfusions: the

limitations of retrospective medical record reviews. Int J Quality Health Care 1996; 8(1): 41–9 467 Downloaded from https://academic.oupcom/milmed/article/185/3-4/461/5607588 by guest on 27 March 2021 11. Nijboer JM, van der Horst IC, Hendriks HG, ten Duis HJ, Nijsten MW: Myth or reality: hematocrit and hemoglobin differ in trauma. J Trauma 2007; 62(5): 1310–2. 12. Brunken GS, França GVAD, Luiz RR, Szarfarc SC: Agreement assessment between hemoglobin and hematocrit to detect anemia prevalence in children less than 5 years old Cad Saúde Colet 2016; 24(1): 118–23. 13. Graitcer PL, Goldsby JB, Nichaman MZ: Hemoglobins and hematocrits: are they equally sensitive in detecting anemias? Am J Clin Nutr 1981; 34(1): 61–4. 14. Abdulazeez A, Muhibi MA: Calculated haematocrit gave a better prediction of anaemia than observed haematocrit in patients with haemorrhage and under aged children in Central Nigeria. Br J Med Med Res 2014; 4(23): 4044–9. 15. Insiripong S, Supattarobol T,

Jetsrisuparb A: Comparison of hematocrit/hemoglobin ratios in subjects with alpha-thalassemia, with subjects having chronic kidney disease and normal subjects. Southeast Asian J Trop Med Public Health 2013; 44(4): 707–11. 16. World Health Organization: Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity 2011 Available at https:// www.whoint/vmnis/indicators/haemoglobinpdf accessed on 06 July 2019. 17. Myhre KE, Webber BJ, Cropper TL, et al: Prevalence and impact of Anemia on basic trainees in the U.S Air Force Sports Med Open 2015; 2: 23