Adjusting Haemoglobin Values for Altitude Maximizes Combined Sensitivity and Specificity to Detect Iron Deficiency among Women of Reproductive Age in Johannesburg, South Africa

Abstract

In South Africa, haemoglobin (Hb) is measured to screen for iron deficiency (ID). However, low levels of Hb are only a late stage indicator of ID. Furthermore, Hb values are generally not adjusted for altitude even though recommended by WHO. We determined the Hb threshold with the highest combined sensitivity and specificity for detecting ID among South African women living at 1700 m above sea level. In a cross-sectional study of 492 18–25-year-old women, we measured Hb and iron status biomarkers. Using receiver operating characteristic curves, we determined the Hb threshold with maximum Youden Index for detecting ID. This threshold of <12.35 g/dL resulted in a 37.2% anaemia prevalence (20.9% IDA), and sensitivity and specificity of 55.7% and 73.9%, respectively. The WHO altitude-adjusted threshold of <12.5 g/dL resulted in a 39% anaemia prevalence (21.3% IDA), and sensitivity and specificity of 56.8% and 70.8%, respectively. In contrast, using the unadjusted Hb cut-off of <12 g/dL resulted in a 18.5% anaemia prevalence (12.6% IDA), and sensitivity and specificity of 35.1% and 88.6%, respectively. In this sample of South African women of reproductive age an Hb threshold <12.35 g/dL had the highest combined sensitivity and specificity for detecting ID. The diagnostic performance of this Receiver operating characteristic curve-determined threshold was comparable to the altitude-adjusted threshold proposed by WHO. Thus, clinical and public health practice in South Africa should adopt adjustment of Hb for altitude to avoid underestimation of ID and missing women in need for intervention.

Food insecurity, diet quality and body composition: data from the Healthy Life Trajectories Initiative (HeLTI) pilot survey in urban Soweto, South Africa

“…Anthropometric data collection followed World Health Organization (WHO) anthropometry standards, and all research assistants were trained by trainers from WHO. Haemoglobin (Hb) levels (g/dl) were assessed using a HemoCue, and anaemia was classified as a Hb level of <12•5 g/dl based on the WHO's altitude-adjusted threshold (20,21) .…”

Phenotypic differences between highlanders and lowlanders in Papua New Guinea

“…In order to minimise the impact of malaria prevalence differences between PNG lowlands and highlands, we removed people suffering from anaemia from the haemoglobin comparison analysis, following the World Health Organization (WHO) standard cut-offs. These cut-offs have been adjusted to limit the underestimation of anaemia among PNG highlanders following the altitude adjustment suggested by WHO (exclusion of non-pregnant lowlander women < 12 g/dl, lowlander men <13 g/dl, exclusion of non-pregnant highlander women < 13.3 g/dl, highlander men <14.3 g/dl) [69,104]. This filter did not change the significant difference of haemoglobin concentration between PNG highlanders (mean: 16.34 g/dl [95% ) and lowlanders (mean: 14.81 g/dl [95% CI 14.31-15.33]) (Table 1, S4 and S7 Figs).…”

Building knowledge, optimising physical and mental health and setting up healthier life trajectories in South African women (Bukhali): a preconception randomised control trial part of the Healthy Life Trajectories Initiative (HeLTI)

“…The trial was designed following the Standard Protocol Items (Recommendations for Interventional Trials (SPIRIT) 2013 statement). Through extensive qualitative (focus groups, in-depth individual interviews and stakeholder engagement)18–23 and epidemiological research,24–31 we identified our young women (18–28 years) as the target group given that a high proportion these women are already either overweight or obese and most will have their first child during this age range, and developed the intervention package. We initially opted for a cluster randomised study design in order to included community peer group sessions as part of the intervention.…”