Heterogeneous hemoglobin lower thresholds in clinical laboratories
Authors: Katherine S. Colman, Erica M. Wood, Barbara De La Salle, Simon J. Stanworth, Sant‐Rayn Pasricha
Journal: American Journal of Hematology (2018)

Accurate and harmonized definitions of anemia are critical for clinical management of patients and for ascertaining the epidemiology of the problem in public health. We surveyed laboratories participating in the UK External Quality Assurance programme (The UK NEQAS, a charitable consortium of external quality assessment laboratories), to determine the thresholds they used to define anemia. We found that while most laboratories provide sex-specific thresholds, few laboratories used distinct thresholds in pregnancy, children, postmenopausal women, or elderly people. Lower thresholds (often used clinically to define anemia) varied markedly between laboratories, especially among women, children and in pregnancy. Most laboratories cited textbook sources for their thresholds; the thresholds used were often discordant with that cited in the reference. The evidence underlying hemoglobin thresholds to define anemia remains limited, thus heterogeneity between laboratories is perhaps not unexpected. Anemia is considered to exist when the hemoglobin concentration is inadequate for physiologic oxygen carrying needs. Accurate definition of anemia is critical for clinical practice, understanding anemia epidemiology, and planning public health interventions. However, there is uncertainty about the hemoglobin thresholds at which anemia should be defined. For example, in adult males, the World Health Organization (WHO) defines anemia as hemoglobin <130 g/L,1 whereas the United States (US) Centers for Disease Control and Prevention (CDC) defines anemia as hemoglobin <135 g/L.2 In pregnancy, CDC varies the definition of anemia by gestational age (CDC 2011), whereas WHO maintains <110 g/L throughout (WHO 2011). Furthermore, prominent hematology textbooks cite a variety of thresholds. Using WHO definitions, anemia affects 41.7% of children and 32.8% of women worldwide (predominantly, but not exclusively, in low income countries).3 We assessed the degree of harmonization of anemia definitions used in clinical practice among the 808 laboratories registered with The UK NEQAS. NEQAS provides a comprehensive external quality assessment service to most laboratories supporting hospitals in the UK National Health Service (NHS) in addition to other international sites. Approval was granted by Monash University's Human Research Ethics Committee (CF16/1925–2016000981). Of the 600 clinical laboratories or diagnostic sites registered with NEQAS to which this survey was relevant and circulated, 208 laboratories (35% overall, 60% for UK respondents) across 14 countries responded, predominantly from Europe (199/208, 95.7%), including two-thirds UK (140/208, 67.3%) (Supporting Information Table S1). Questionnaires from NEQAS are completed by the laboratory manager, similar senior scientist, or medical or scientific head of department. More laboratories cited textbooks (82/208, 39.4%), predominantly Dacie and Lewis’ Practical Hematology (52/208, 24.9%), than WHO guidelines (23/208, 11.1%). Twenty-three percent (48/208) reported calculating their own reference ranges (Figure 1A). Most laboratories provided sex-specific adult [male (187/208, 89.9%) and female (164/208, 78.8%)] hemoglobin thresholds to define anemia (Figure 1B). Figure 1C shows thresholds used. The most common threshold in adult males was <130 g/L (126/187 laboratories, 67.7%, range 120–140 g/L). For females, 21% of laboratories (44/208) used the same threshold as for males; among those using separate thresholds, half used <115 g/L (81/164, 49.4%, range 90–125 g/L). Only 8% of laboratories (16/208) used separate thresholds for pregnancy (range 90–120 g/L), and 4% (8/208) for premenopausal and postmenopausal females. Sisty-one percent of laboratories (127/208) used specific thresholds for children. The most common threshold was <110 g/L in young children (1–5 years, 40/127 laboratories, 31.5%, range 90–130 g/L) and <115 g/L in older children (5–13 years, 80/127, 63.0%, range 90–130 g/L). Only 10% of laboratories (21/208) provided distinct thresholds in the elderly, with just one providing sex-specific (>65 years) thresholds. No laboratory varied thresholds by ethnicity. Source and nature of hemoglobin thresholds used to define anemia by laboratories. (A) Source of ranges used by laboratories. (B) Populations with individualized thresholds to define anemia. (C) Hemoglobin thresholds used to define anemia by laboratories Hemoglobin thresholds were typically at or below those recommended by WHO. For males, 67.7% of laboratories (126/187) with sex-specific thresholds used <130 g/L, consistent with WHO, and 7.6% (14/187) used lower thresholds. For females, 38.4% (63/164) used <120 g/L consistent with WHO, while most (99/164, 60.4%) used lower thresholds. For children 1–5 years, 31.5% (40/127) used <110 g/L consistent with WHO, and 37.0% (47/127) used lower thresholds. For children 5–13 years, 63.0% (80/127) used <115 g/L consistent with WHO, and 24.4% (31/127) used lower thresholds. Among laboratories reporting having sourced thresholds from published references, over 35% were using thresholds discordant with the recommendation in that resource for males, almost half were discordant with the quoted reference in females, and over 60% were discordant with the cited reference in young children (Supporting Information Table S2). Measurement of hemoglobin concentration is one of the most commonly requested and widely available pathology tests. Anemia diagnosis is fundamental to primary care, perinatal medicine, internal medicine, geriatrics, and perioperative care. However, our findings indicate considerable heterogeneity in lower limits of hemoglobin ranges used across laboratories. The underlying causes of this variation likely reflect a lack of high quality evidence based guidelines and hence consensus on the optimal thresholds to deploy. Crucially, thresholds used by laboratories often do not reflect the recommendation of their quoted source. Variation in analytic methodology does not justify variation in thresholds between laboratories, as international reference standards have been available for calibration and standardization of hemoglobin measurements on automated analyzers and hemoglobinometers (including point-of-care instruments) for 40 years.4 Current hemoglobin thresholds to diagnose anemia recommended by WHO were proposed in 19685 based on five relatively small studies conducted in Europe and North America, and without representation from diverse ethnic groups, ages, or countries. Laboratory and epidemiologic techniques have developed considerably since then, however the recommendations have been maintained with minimal adjustment over subsequent decades.1 Whether these thresholds accurately define anemia, and whether they are appropriate across all populations, is debatable. For example, African American populations appear to have 10 g/L lower hemoglobin concentrations than Caucasians.6 Key expert sources such as the UK National Institute for Health and Care Excellence and the Royal College of Pathologists of Australasia do not make specific recommendations but leave individual laboratories to define their thresholds.7, 8 This appears to have resulted in a large variety of sources, with potentially differing thresholds, being deployed by laboratories. However, in many cases, laboratories do not seem to be using the thresholds recommended by their sources. The lack of a high quality, accepted set of evidence-based guidelines to define anemia may thus underlie heterogeneity between laboratories. The lower limit of the reference range is often used clinically to define anemia although some clinicians may apply independent criteria to diagnose anemia or may apply tailored criteria based on patient-specific factors. Further work is urgently required to clarify, establish and harmonize hemoglobin thresholds to diagnose anemia. As well as statistical definitions, thresholds may need to consider where adverse functional clinical (e.g., fatigue), or developmental (e.g., cognitive development in children) outcomes are seen; or where investigation is essential to exclude underlying diseases. WHO has established a programme of work to review hemoglobin thresholds used to define anemia. An online expert consultation identified priority areas including variations in thresholds by sex and age, definitions of anemia severity, adjustments of definitions by elevation above sea level, and hemoglobin concentrations associated with adverse developmental outcomes in infants and birth outcomes in mothers.9 Definitive studies characterizing the hemoglobin thresholds that define anemia across populations, ages and ethnicities, with correlation to clinical and functional outcomes, are essential to enable harmonization in interpretation of this crucial biomarker. All authors contributed toward the study design and development of the questionnaire, BD facilitated running the questionnaire, KC and SP analyzed the data, and KC and SP wrote the manuscript, which was edited and approved by all authors. SP has received a consultancy from WHO to provide assistance with preparation of the Technical Meeting: Use and interpretation of hemoglobin concentrations for assessing anemia status in individuals and populations (December 2017). The other authors have no competing interests to declare. The authors thank the UK NEQAS for distributing the questionnaire on our behalf, and all responding laboratories. We thank the John Radcliffe Hospital laboratory for piloting the questionnaire to ensure it was clear and readily answerable. Additional Supporting Information may be found online in the supporting information tab for this article. Supporting Information Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.