Use of Point-of-care Haemoglobin Tests to Diagnose Childhood Anaemia in Low-and Middle-Income Countries: A Systematic Review

Objectives Anaemia is a major cause of mortality and transfusion in children in Low- and Middle-Income Countries (LMICs), however current diagnostics are slow, costly, and frequently unavailable. Point-of-care haemoglobin tests (POC(Hb)Ts) could improve patient outcomes and use of resources by providing rapid and affordable results. We systematically reviewed the literature to investigate what, where and how POC(Hb)Ts are being used by health facilities in LMICs to diagnose childhood anaemia, and to explore challenges to their use. Methods We searched a total of nine databases and trial registries up to 10th June 2022 using the concepts: anaemia, POC(Hb)T, LMIC and clinical setting. Adults ≥21 years and literature published >15 years ago were excluded. A single reviewer conducted screening, data extraction and quality assessment (of diagnostic studies) using QUADAS-2. Outcomes including POC(Hb)T used, location, setting, challenges and diagnostic accuracy were synthesised. Results Of 626 records screened, 41 studies were included. Evidence is available on the use of 15 POC(Hb)Ts in hospitals (n=28, 68%), health centres (n=9, 22%) and clinics/units (n=10, 24%) across 16 LMICs. HemoCue (HemoCue AB, Ängelholm, Sweden) was the most used test (n=31, 76%). Key challenges reported were overestimation of haemoglobin concentration, clinically unacceptable limits of agreement, errors/difficulty in sampling, environmental factors, cost, inter-observer variability, and supply of consumables. Five POC(Hb)Ts (33%) could not detect haemoglobin levels below 4.5g/dl. Diagnostic accuracy varied, with sensitivity and specificity to detect anaemia ranging from 24.2-92.2% and 70-96.7%, respectively. Conclusions POC(Hb)Ts have been successfully utilised in health facilities in LMICs to diagnose childhood anaemia. However, limited evidence is available, and challenges exist that must be addressed before wider implementation. Further research is required to confirm accuracy, clinical benefits, and cost-effectiveness.


INTRODUCTION
Anaemia is a major global health problem, affecting over 1.8 billion people worldwide [1,2].The condition is characterised by reduced blood haemoglobin (Hb), resulting in increased morbidity and mortality.Definitions vary by age, with anaemia and severe anaemia classified as Hb < 11 g/dL and Hb < 7 g/dL in children aged 6-59 months [2].Prevalence and years lived with disability are highest in Sub-Saharan Africa and South Asia where nutrient deficiencies, infectious diseases and haemoglobinopathies are common [1,3].Children under 5 years of age are most vulnerable, with an estimated prevalence of 56.5% in low-and middleincome countries (LMICs) [4].
Severe anaemia is life-threatening and accounts for many hospital admissions in Sub-Saharan Africa.A large randomised controlled trial (RCT) investigating fluid bolus on mortality in hospitalised African children with severe infection, found 33% of presented children had Hb level < 5 g/dL and this resulted in increased mortality (FEAST) [5,6].Severe anaemia often requires emergency blood transfusion to restore Hb levels.However, this requires efficient diagnosis and availability of donated blood for effective treatment.This poses significant challenges in LMICs, where laboratory analysis is often lengthy, and stock-outs of blood are frequent [7].Delays in transfusions are common [8].Results from FEAST show that 52% of severely anaemic children died when not transfused within 8 h, with 90% of deaths occurring within 2.5 h [5,6].Therefore, prompt transfusion is critical to save lives.
Haematology analysers are the routine diagnostic method used to diagnose anaemia.However, equipment is expensive, requires electricity, trained personnel, and regular supply of reagents.This leads to them being often unavailable in LMICs, resulting in inaccurate diagnosis by clinical assessment and inappropriate use of transfusion [9][10][11].Point-of-care haemoglobin tests (POC(Hb)T) have been developed to help address these issues.These tests should be Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free and Deliverable, according to World Health Organisation (WHO) ASSURED criteria [12].They are less invasive and provide immediate results [13].
Although several POC(Hb)Ts have been developed and evaluated in recent years, it is unclear to what extent POC(Hb)Ts have been employed to diagnose anaemia in underserved populations.Understanding where and what POC(Hb)Ts are currently used by health facilities and the barriers to their use, will help guide work to improve their availability and allow safe implementation.
The aim of this study was to conduct a systematic review to explore and summarise available evidence on POC(Hb)T use in children in LMICs.Using data from published literature and trial registries, we address the following questions: what, where and how are POC(Hb)Ts being used by health facilities in LMICs to diagnose childhood anaemia, and are there challenges to their use?To the best of our knowledge, our systematic review was the first to address these questions and therefore provides invaluable evidence for policymakers.

Literature search
We conducted a systematic review, reported in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines [24].We aimed to identify all published and unpublished literature using POC(Hb)Ts in children in LMICs.We searched six bibliographic databases: MEDLINE, EMBASE and Global Health via OVID, Web of Science, LILACS and Cochrane Central Register of Controlled Trials.Clinical trial registries (WHO International Clinical Trials Registry Platform and ClinicalTrials.gov)were searched for unpublished trials.Pro-Quest Dissertations and Theses were also searched.Entire platforms were searched up to 10 June 2022 and English language filters applied.Relevant journals, articles and authors were manually searched to identify missing literature; this included searching reference lists of included studies.
Search terms were based on four key concepts: anaemia, POC(Hb)T, LMIC and clinical setting.LMIC filters were provided by Cochrane Collaboration and updated according to World Banks Classification 2022 [25,26].Full details of the search strategy are outlined in Table S1.

Selection criteria
We included all RCTs and observational studies using POC(Hb)Ts to diagnose anaemia in children (aged 0-20 years) attending health facilities, published/registered within the last 15 years.Reviews, at-home POC Hb testing, testing from non-blood samples, high-income countries, and non-English or non-full text publications were excluded, as were studies not performing POC(Hb)Ts immediately at the site of care (laboratory or delayed sample analysis).There were no restrictions based on child presentation or characteristics to ensure generalisability in the paediatric population.

Data extraction
Results were exported to Endnote 20 and Rayyan systematic review management software.Duplicates were removed and further checked manually.The primary reviewer (RB) doublescreened titles and abstracts for relevance using pre-specified inclusion/exclusion criteria.Potentially eligible studies were further screened by full-text assessment.Any uncertainties on study eligibility were discussed and resolved by consensus with co-authors (ECG, AS).
We extracted: study characteristics, location, setting, POC(Hb)T(s) used, sample, prevalence of mild/moderate/ severe/overall anaemia or mean Hb concentration, diagnostic accuracy and challenges to test use reported by study authors.All data were collected using three piloted data extraction tools (study characteristics, challenges and diagnostic accuracy) created in Microsoft Word (Tables S2 and S3; Table 3).

Quality assessment
The primary reviewer (RB) assessed risk of bias (RoB) and applicability concerns using an adapted QUADAS-2 tool (Table S4) [27].Due to limited evidence on HemoCue (HemoCue AB, Ängelholm, Sweden) device accuracy in this population and setting, studies using HemoCue as reference standard were judged high RoB for domain three.'Unclear' judgement was only made when insufficient evidence was reported.

Data analysis
Extracted data were synthesised from all included studies and summarised in groups to answer the review question: study characteristics, POC(Hb)Ts, location/setting and challenges.Median and interquartile-range (IQR) were calculated for test sensitivity and specificity using Microsoft Excel.Due to differences in cut-offs used to define anaemia and severe anaemia across included studies and age groups, we summarised data according to how it was reported in papers (severe or overall anaemia) rather than using WHO definitions.For diagnostic studies, test sensitivity and specificity were summarised by including cut-offs of Hb < 5 g/dL and Hb < 7 g/dL for diagnosis of severe anaemia.Metaanalysis was not conducted due to insufficient data available for individual POC(Hb)Ts.

Study characteristics
Seven hundred forty-two records were identified from bibliographic databases and 24 from trial registries (Figure 1).One hundred seventy-nine duplicates were removed and 587 records were title and abstract screened.Four hundred thirty-nine records were excluded, leaving 148 records for full-text assessment.Thirty-nine additional records were identified from reviewing related articles and citation lists.In total, 45 records from 41 studies met inclusion criteria and were included in our review [3,5,6,13,15,19,22,. Figure 1 shows reasons for exclusions.

DISCUSSION
We systematically reviewed the literature to explore POC(Hb)T use in children in LMICs.Using data from published literature and trial registries, we found evidence on the use of 15 different POC(Hb)Ts by health facilities across 16 LMICs in the last 15 years to diagnose childhood anaemia; from 41 studies.Thirty-nine studies (95%) were conducted in Africa, indicating little evidence is available outside this region.We found that, to date, HemoCue is the most widely utilised test in this population and setting.Our results represent a relatively small proportion of commercially available and assessed POC(Hb)Ts, suggesting limited evidence is available in children [17,[66][67][68][69][70].Imperfect diagnostic accuracy, sampling errors, environmental factors and costs were key challenges reported for POC(Hb)T use.
Five POC(Hb)Ts (33%) could not detect Hb levels below 4.5 g/dL.This is important because many children with severe anaemia in LMICs have Hb < 4 g/dL [3,71] and, for uncomplicated severe anaemia, WHO guidelines recommend blood transfusions only for children with Hb < 4 g/dL.Three studies in our review reported mean Hb concentration by POC(Hb)T < 4 g/dL and five additional studies reported Hb values below this level [3,5,33,37,44,47,50,55].The WHO guidelines for the management of children with severe anaemia and the transfusion algorithm developed based on results from TRACT use a cut-off of Hb < 4 g/dL to determine which children require transfusion in the absence of other severity signs [23,72].Therefore, Mission Hb (ACON Laboratories, USA), I-STAT, Aptus (Entia, UK), Rad-67 (Masimo, USA) and Pronto (Masimo, USA) are not currently suitable for identifying severe anaemia in this population.It is worth noting however, that I-STAT, Rad-67 and Pronto measure additional parameters besides Hb and haematocrit, increasing their utility.URIT-12 (URIT, China) and HCS have a Hb cut-off of 4 g/dL and so accuracy detection at this level must be further investigated.We identified several challenges to POC(Hb)T use that need addressing before wider implementation.No POC(Hb) T showed excellent diagnostic accuracy across all measurements and therefore may not meet all ASSURED criteria [12].Five studies reported overestimation of Hb concentration in eight POC(Hb)Ts (Table 2) [15,29,32,49,58].This is vital since it could result in misclassification of severity of anaemia and therefore prevent truly eligible children from receiving a lifesaving transfusion or appropriate treatment.In contrast, underestimation of Hb levels by POC(Hb)Ts has been reported in children, causing unnecessary use of scarce resources and exposure of children to transfusion-related risks [73,74].A previous review of HemoCue found underestimation of Hb most frequently reported, with few studies reporting overestimation of Hb concentration [75].These conflicting findings could be explained by variations in child Hb level [15,[76][77][78].
Similarly, wide LOA means estimated Hb values could span all categories of anaemia.Our results show seven diagnostic studies and eight POC(Hb)Ts exceeded the clinically acceptable accuracy of upper and lower LOA within 1 g/dL (Table 3) [15,19,29,47,49,54,58].This suggests within-subject variation is too large to provide a clinically meaningful diagnosis.These results are in line with a previous systematic review including adults and children in mixed settings [79].However, a different review has shown clinically acceptable LOA [80].Clinicians should be aware of these LOA when basing clinical decisions solely on these Hb estimations.We found substantial variation in test sensitivity to detect anaemia and severe anaemia, with lowest values reported for HCS and Rad-67 [29,58].This is contrary to a previous review that identified lowest sensitivity to detect anaemia for HemoCue301 (22.6%) and highest sensitivity for HCS (99.3%) out of 6 POC(Hb)Ts [81].Our median values for test sensitivity and specificity to detect anaemia were moderate, suggesting some children would receive a false negative result.
Variation in test performance across studies in our review and with previous literature has several possible explanations.First, nine studies in our review were judged high RoB for at least one domain [15,19,29,31,49,55,58,60,63].Differences in anaemia prevalence, geographical factors (temperature, altitude and humidity), reference test, transportation and storage of consumables, sampling technique and training could also explain discrepancy [15,82,83].Three studies did not use thresholds for severe anaemia defined by WHO for the assessment of sensitivity and specificity (Hb < 5 g/dL), limiting evidence synthesis and contributing to disparity [19,29,55].Lastly, two included studies used different sources of sample for the reference method and POC(Hb)T, and five included diagnostic studies used venous samples for POC(Hb)T [15,19,47,49,54,58,60].This could explain variation due to known differences in capillary and venous blood [84].
These real-life factors pose a challenge to POC(Hb)T use.There is a need for standardised training protocols to reduce errors in sampling technique and interpretation of colour-based tests.Competency of staff and therefore performance should increase as these tests become routine practice.Our findings also suggest five POC(Hb)Ts used may not be suitable for use in some LMICs due to possible device failure at high temperature (>30 C) (Table 1) [15,19,32,35,39,42,[50][51][52]57].
Moreover, we identified analyser costs and lack of supply of consumables as challenges to POC(Hb)T use.Although upfront costs are relatively high, particularly for noninvasive and HemoCue devices, it is the recurrent, per test costs that pose an obstacle to sustained use in LMICs and could explain the lack of supply of microcuvettes and cartridges [85].Total cost of POC tests must be weighed against their benefits such as earlier diagnosis, reduced morbidity and mortality, improved patient satisfaction and decrease of unnecessary referrals, and additional testing [86].Use of POC(Hb)Ts with electronic decision support algorithms could enhance their cost-effectiveness in triage of sick children.However, only one included study adopted this approach and therefore this requires further research [42].The novel colour-based assay offers a significant cost advantage at 0.26 USD per test, however further evidence on its use is required.Other affordable technologies, such as smartphone-based colorimetry are at early stages of development for identifying severe anaemia in LMICs [87].
Key strengths of our review were wide inclusion criteria and adherence to systematic review methods.This allowed a comprehensive synthesis of POC(Hb)T use in this population and setting.Ongoing trials were included and therefore reduced publication bias.Furthermore, we assessed RoB and applicability of included diagnostic studies to evaluate the reliability and validity of findings on POC(Hb)T performance.
Our review has limitations.A single reviewer (RB) screened results, adapted QUADAS-2 tool and judged study inclusion eligibility and RoB and applicability concerns.However, records were screened twice to minimise risk of missing relevant articles and uncertainties were resolved by consensus with co-authors (ECG, AS).We searched a restricted number of databases and trial registries; however, they were the largest and most renowned databases, specific to the subject area.Other methodological limitations include exclusion of reviews, non-full-text or non-English articles and studies published over 15 years ago.Only 13 studies (32%) reported challenges to POC(Hb)T use and therefore our review may be subject to reporting bias if not all challenges were reported.We only assessed data from published literature and trial registries.Clinical trials/studies may not represent the total use of POC(Hb)Ts and may be atypical due to trial funding and supply of tests and consumables.
Another limitation of our work is our focus solely on tests used in children.Our decision to focus on tests available for children was driven by the requirement to be able to detect lower haemoglobin levels in children than is needed for adults, given the different thresholds for defining severe anaemia in these groups [88,89].However, by excluding studies that looked at POC(Hb)Ts used only in adults, we may have missed some relevant studies that may be relevant for children as well.Different studies used different definitions of anaemia and severe anaemia, and we report the definitions used, as we were unable to convert this to standardised definitions.There is debate at the moment about what thresholds should be used [88,89], and WHO guidelines for malaria differ in the thresholds used to those in guidelines for care of children in hospital [72,90].

Further research
Diagnostic accuracy data for this population and setting was available for only 10 POC(Hb)Ts.This finding is critical, since POC(Hb)Ts must be validated in the population and setting of their intended use before wider adoption.Further high-quality research on test accuracy, particularly using capillary samples, is warranted to assess performance in various settings and address discrepancy between studies.There is currently insufficient data to conduct meta-analysis on individual POC(Hb)Ts in this population and setting.Further research should ensure data and results can be combined with previous studies for meta-analysis.
Very few studies used POC(Hb)Ts in guiding and monitoring transfusion [5,22,37].Therefore, further research is essential to evaluate use with the transfusion algorithm and impact on patient-centred outcomes, time to transfusion and usage of blood supply.Further research is also required to understand the clinical and resource implications of under/overestimating Hb levels, especially near the cut-off for severe anaemia.The challenges identified in our review also stress the need for further development of some POC(Hb)Ts and standardised training procedures.For example, by expanding detection ranges to include lower Hb levels and to enable higher operating temperatures.

CONCLUSIONS
In conclusion, 15 POC(Hb)Ts have been successfully utilised in health facilities across 16 LMICs to diagnose childhood anaemia of various aetiologies.However, several challenges to their use exist and must be addressed.We found Hemo-Cue301, HemoCue801 and HemoControl (EKF Diagnostics, UK) offer the most suitable Hb detection ranges and operating temperatures (<40 C) for use in this setting.However, we identified no evidence on diagnostic accuracy for HemoCue801 and HemoControl.We therefore recommend HemoCue301 as the best available POC(Hb)T to diagnose childhood anaemia in LMICs, based on available evidence.However, imperfect diagnostic accuracy is a drawback and must be weighed against benefits in costs, safety, convenience and improved clinical outcome.Further research is essential to confirm these benefits and diagnostic accuracy in these settings.Routine use of POC(Hb)Ts may significantly reduce child mortality in LMICs, where laboratory analysers are often unavailable and anaemia prevalence is high.
Diagnostic accuracy of included POC Hb tests.
Note: Challenges reported for included studies in order of most frequently reported (by study authors).Abbreviations: g/dL, grams per decilitre; Hb, haemoglobin; POC, point-of-care; QC, quality control.a HemoCue 201+ (wicking) and Pronto overestimated Hb concentration for anaemic children only.b Authors reported overestimation of Hb/clinically unacceptable accuracy based on pooled children and adult data.T A B L E 3 1.A: ?B: Test performance data from all included diagnostic accuracy studies.Tests presented in order of most used (same as Table1).Risk of Bias and Applicability 1. = Unknown.Wicking: Standardised method used to draw capillary blood directly from skin into the microcuvette.Gravity: Non-standardised method where capillary blood is first transferred onto a surface before drawn into the microcuvette.Correlation data rounded to 2 decimal places.Abbreviations: CCC, concordance correlation coefficient; CI, confidence interval; g/dL, grams per decilitre; HCS, Haemoglobin Colour Scale; ICC, intraclass correlation coefficient; LOA, limits of agreement; POC Hb test, point-of-care haemoglobin test; r, Pearson's correlation coefficient; SA, severe anaemia; ρ Note:c , Lin's concordance correlation coefficient.