Public Health Screening Project

From Ni Wiki

Introduction

This manual was developed to introduce individuals (laypersons, community health workers, nurses, doctors, administrators) to the HbCS system in the specific context of Guyana. Whenever possible, we strongly encourage that the HbCS be introduced in a comparative manner with the currently used technique (ex. HemoCue in this instance). A direct comparison will allow individuals to assess the strengths and weaknesses of both systems in a first-hand manner.

Objectives

At the end of the training, the user should be able to:  Understand the strength and weaknesses of the HbCS  Identify settings where the HbCS would be an appropriate and useful device  Reliably measure blood haemoglobin concentration using the HbCS  Recognize situations and practices which do not comply with the HbCS instructions for use

Background

Anaemia is one of the major health problems around the world. In developing countries (including Guyana), the prevalence of anaemia is often greater than 50% in pregnant women and young children. Given the global impact of anaemia on public health, the measurement of blood haemoglobin is essential to diagnose anaemia and is an important prerequisite in many other health issues.

HbCS

The idea behind the haemoglobin colour scale is not new. Based on the property that blood with different amounts of haemoglobin dries different colours, Tallqvist and others proposed the idea of a colourimetric assay as early as 1900. However, this technique was soon regarded as inaccurate and abandoned. Recently, the pressing need for a simple, inexpensive, and reliable measurement of haemoglobin led the World Health Organization to revisit the idea and employ modern technology to correct many of the historical problems and perfect this concept.

Using spectrometric analysis and a computerized printing process, a reference colour scale was developed on a special fade and UV-resistant paper. The scale consists of a range of six colour shades representing haemoglobin values from 4-14 g/dL and the severity of the anaemia in clinical terms. The scale is supplied with special test strips which provide uniform absorption, dispersion, and drying of blood for greatest colour consistency and thus accuracy.

In validation and field studies by the World Health Organization and others since 1995, the HbCS has achieved a sensitivity of 80-94% and a specificity of 91-98% with the HemoCue as reference. For severe anaemia the scale was 95% sensitive and 99.6% specific. In screening blood donors the scale was 98% accurate, which was more reliable than copper sulfate. The manufacturing of the test has been contracted to Copack GmbH (http://www.copackservice.de) and became commercially available in 2001.

The HbCS can potentially play a role in both curative and preventative health services. Some example situations where the HbCS system may be useful:

 Anti-Retroviral Programs – pretreatment anaemia screening to guide appropriate therapy and monitor disease related exacerbations of anaemia  Blood Transfusion Services – detecting and excluding anemic donors  Malaria and Nutrition Programs – screening for anaemia and measuring success of interventions  Maternal and Child Health Clinics – for routine screening and detection of anaemia severity to guide management strategies

Comparison of HbCS with HemoCue

HbCS HemoCue Equipment Cost None $350 (US) Cost per Test $0.02 (US) $0.75 (US) Tests Expire No Yes Measurement Type Semi-quantitative Quantitative User Variability Low* None Accuracy High Very High Power Source None Batteries Portability Very High Medium

• with proper training, shading represents an advantage

In the areas of specialized training, maintenance, and timeliness of results, both methods excel and neither demonstrates a clear advantage.

Instructions for Use

Always use approved blood collection techniques and safely dispose of hazardous materials including used swabs, lancets, test strips, etc. Use gloves when collecting blood and handling the colour scale.

Apply a drop of blood large enough to form a stain about 1 cm in diameter on the test strip. The drop should be applied to the absorbent “puffy” die of the strip that is fibrous in appearance. Make sure the stain covers the entire area of the aperture on the scale. Equally, too much blood may take too long to dry.

Once the blood has been applied, wait 30 seconds and read the scale immediately by placing the strip at either the darkest or lightest colour and sliding the stain up or down until the best match is found. Do not delay reading the test strip as the colour of the stain will change over time. If the stain appears to lie between two shades on the scale, record the mid-value of the two colours. If in doubt between two colours, record the lower value.

An approximate 45° angle has been found to be optimal for reading the test, although you should tilt the book such that you can best distinguish the different shades of red. Do not read the scale in any shadow, including your own. The scale should be read directly under artificial light, or in a well-lit area with the daylight (but not direct sunlight) coming in from over your shoulder.

Incorrect use of the scale may result in incorrect estimations.

Common Mistakes

The manufacturer states that in a validation study most results were accurate to within 1-1.5 g/dL. Most of the errors were found to be largely a result of incorrect technique including:

 Not waiting for 30 seconds before reading the results  Reading the results after 2 minutes  Reading in a shadow or direct sunlight  Inadequate size of blood drop

Conclusions

The HbCS is a reliable system to estimate haemoglobin provided that the instructions are strictly followed. It is ideal for use at the community level and in rural, low-tech areas. The HbCS is intended for use in the absence of laboratory haemoglobinometry and does not replace a laboratory test. Users who have difficulty distinguishing colour variation should not attempt to use the scale.

Acknowledgments

We would like to thank Nourish International for the haemoglobin colour scales and their continued support of the author. We are heavily indebted to Dr. Ramasaran, Mr. Ramu, Mrs. Howard and all of the staff at the Regional Health Centers for providing valuable feedback.

References

1. World Health Organization, Department of Essential Health Technologies. Haemoglobin Colour Scale Operational Research Agenda and Study Design. 2004

2. Stott GJ, Lewis SM. A simple and reliable method for estimating haemoglobin Bulletin of the World Health Organisation, 1995, 73:369-373

3. Lews SM, Stott GJ, Wynn KJ. An inexpensive and reliable new haemoglobin colour scale for assessing anaemia. Journal of Clinical pathology, 1998, 51: 21-24

4. Montresor A. et al. Field trial of a Haemoglobin colour Scale: an effective tool to detect anaemia in preschool children. Tropical medicine and International Health, 2000, 5; 129-133

5. Copack GmbH. Haemoglobin Colour Scale Information Leaflet. 2001.

Practice Tests

The instructor will provide a blood sample for you to practice on. Analyze the haemoglobin from the sample using the HbCS in strict accordance with the instructions. If possible, also analyze the sample using the HemoCue system. Record your results in the tables below. Report your result to the instructor who will compile all the values and present the average value recorded by all the participants followed by the true haemoglobin concentration of the sample. If your result varies from the true haemoglobin value by more than ± 1 g/dL, try repeating the HbCS test until you can better match the colour. Seek help in interpreting your result from other participants and try and see if your readings improve as you analyze more samples.

Results Using HbCS

Trial Hb Result Average Value True Value (g/dL) 1 2 3 4 5

Results Using HemoCue

Trial Hb Result Average Value True Value (g/dL) 1 2 3 4 5