Hemoglobinometer - About an Essential Point-Of-Care Diagnostic Device

Introduction

Estimation of hemoglobin is an accurate indicator for diagnosing anemic disorders. Anemia is a clinical condition where the oxygen-carrying capacity of the red blood cells is reduced resulting in insufficient oxygen supply to all the organs and tissues in the body. Anemia is not a single disease entity. It represents a sign or clinical symptom that arises as a consequence of various disorders. Assessing hemoglobin, a prominent protein in red blood cells becomes an easy and reliable laboratory testing method for detecting anemia. Hemoglobin estimation using a hemoglobinometer is a frequently requested screening test in individuals with symptoms of anemia and also to evaluate the efficacy of treatment interventions.

Why Should Hemoglobin Levels Be Estimated?

Hemoglobin is the predominant component of the red blood cells (RBCs) that constitute about 90 % of the dry weight in a mature red blood cell. It is a specialized metalloprotein that comprises a heme part containing iron and a globin part made up of protein chains. The type of hemoglobin in adults is called adult hemoglobin (HbA) and that present in the fetus is called fetal hemoglobin (HbF).

The most essential function of hemoglobin is oxygen transport in red blood cells. The iron in the heme molecule binds reversibly with oxygen and delivers it to the tissues. It also clears carbon dioxide from the tissues and carries it to the lungs. Thus, hemoglobin is an essential medium of gaseous exchange (oxygen and carbon dioxide) in the body. The protein chains help in the reversible binding of oxygen with iron. Fetal hemoglobin binds with oxygen more readily than adult hemoglobin.

Anemia is characterized by low hemoglobin concentration in the blood or decreased oxygen content in RBCs which is caused by a variety of disorders. Undiagnosed and untreated anemia leads to adverse clinical consequences. It is a major public health problem in developing countries like India. Most of the hemoglobin estimation methods require well-equipped laboratory settings that are not easily available, particularly in rural areas. Hemoglobinometers serve as gold standard methods in evaluating blood hemoglobin content. These devices are reliable, user-friendly, and portable clinical instruments for detecting anemia, especially where minimal lab facilities are available.

What Are the Various Methods for Hemoglobin Estimation?

In recent years different types of methods have been developed and standardized in estimating hemoglobin (Hb). These techniques are broadly classified into -

Invasive Methods - for these methods, the blood sample is collected from the individuals by inserting a needle through the skin which is done by a trained medical provider.

• WHO hemoglobin color scale (HCS).

• Hemoglobinometers are based on the photometry principle (HemoCue and Sahli's method).

• CO-oximetry (based on the spectrophotometry principle).

• Automated hematology analyzers (AHAs).

Noninvasive Techniques - these procedures do not break the skin or physically pierce the body. They use imaging principles and sensors for performing the tests.

• Pulse oximetry.

• Photoplethysmography.

• Optoacoustic method.

• Diffuse reflectance spectroscopy.

• Imaging-based technique.

Each of these Hb estimation methods has its own advantages as well as limitations and is employed in various types of clinical settings depending on their requirement and availability.

What Is Hemoglobinometer?

A haemoglobinometer is a clinical laboratory instrument that measures the amount of hemoglobin (Hb) present in the blood. It is also called a hemochromometer. There are two types of hemoglobinometers currently used in clinical practice. They are -

• Conventional Hemoglobinometers - these methods are based on color development (photometry), where the blood sample is diluted with ceratin reagents and the resulting color is compared in a standardized Hb comparator box. Sahli’s or acid hematin method, cyanmethemoglobin method, and oxyhemoglobin method are some of the manual methods of hemoglobinometers.

• Digital or Portable Hemoglobinometers - they also work in a similar method (reflectance photometry), where the blood sample is loaded in thin strips containing chemical reagents, and the resulting reaction is analyzed by self-calibrated sensors. They also include microprocessor hemoglobinometers.

How Does a Hemoglobinometer Work?

Hemoglobinometer is a specialized photometric device that measures Hb concentration in the blood by correlating to its optical density (liner correlation). The working principle of hemoglobinometers (both conventional and digital) is based on Beer-Lambert’s law.

Beer-Lambert’s Law

• The absorbance (capacity to absorb light) of a pure compound is directly proportional to the absolute concentration of that particular compound.

• A known concentration of an absorbing substance with a definite wavelength is standardized and its absorbance readings are used to calculate the concentration of the unknown absorbing substance.

• Photometry method of hemoglobinometers is based on this law, where the absorbance of the Hb-reagent compound is compared with the absorbance (radiant energy at a particular wavelength)with a standard calibration.

Sahli’s or Acid Hematin Method

• Five microlites of the blood sample is mixed with N/10 HCl (hydrochloric acid) and is converted into acid hematin (brown in color).

• This solution is diluted with distilled water till the color of acid hematin is matched with the standardized brown colored glass of the Hb comparator box.

• The concentration of Hb in the given sample is estimated directly by comparing it with the standard.

Cyanmethemoglobin Method

• This method is internationally recommended for detecting hemoglobin concentration.

• Blood is diluted with a mixture of potassium cyanide and potassium ferricyanide solution.

• Hb is eventually converted into cyanmethemoglobin (HiCN) by the two reagents.

• The absorbance of this solution is measured in a spectrophotometer at a definite wavelength of 540 nm.

• A colorimeter with a yellowish-green filter is also used to read the color wavelength.

Oxyhemoglobin Method

• Oxyhemoglobin is formed when hemoglobin reacts with ammonia.

• The color of the resulting solution is calibrated in a photocolorimeter.

Alkaline Hematin Method

• Sodium hydroxide reacts with hemoglobin to form alkaline hematin.

• The color of alkaline hematin is estimated in a colorimeter at a wavelength of 540 nm.

Digital Hemoglobinometer

• It is a handy (palm-sized) nanoelectronic bio device that has self-calibrated sensors.

• It takes less than 60 seconds for estimating hemoglobin in digital hemoglobinometers.

• Its working principle is based on reflectance photometry.

• Eight milliliters of blood sample is needed.

• Blood is introduced into thin plastic strips containing specific chemical reagents.

• The vial containing strips has a unique digital code that is entered into the device at the time of loading.

• Each pack has 50 sterile lancets for single use.

• The digital hemoglobinometer is both main-electrical as well as battery-operated (rechargeable battery - 3.6 V).

How Are the Results Interrupted in a Hemoglobinometer?

The measured concentration of hemoglobin in the whole blood is expressed in grams per deciliter and denoted as g/dL.

Normal Reference Values of Hb

• Males - 13 to 17 g/dL.

• Females - 12 to 15 g/dL.

WHO (World Health Organization) Cut-off Value for the Presence of Anemia

• Males < 13 g/dL.

• Females < 12 g/dL.

• Pregnant women < 11 g/dL.

What Are the Quality Assurance Protocols Followed for Hemoglobinometers?

Quality assurance testing of hemoglobinometers is done to monitor the manufacturing methods and determine the efficacy of all required calibrations. it identifies the presence of flaws in the device and ensures the accuracy of the readings.

• All technical staff should be well-trained for data handling and instrument operation.

• The reports are frequently assessed by technical experts to ensure quality.

• Appropriate sterilization protocol is followed to ensure the complete destruction of infectious microorganisms and contaminants.

• Regular inspection to detect breakage of instrument parts or altered discoloration of the calibrated standards is required for precise estimation of hemoglobin.

How Are Conventional Hemoglobinometers Beneficial?

Conventional haemoglobinometers have unique features that make them ideal for use, particularly in tropical countries with limited lab facilities. Some of their benefits are as follows -

• Easy and convenient to perform.

• Inexpensive and affordable.

• Used as point-of-care testing or a bedside procedure.

• A minimal requirement for technical expertise

• A reliable reference standard is provided by WHO for direct comparison.

• Used in general clinical practice.

What Are the Advantages of the Digital Hemoglobinometer?

Digital hemoglobinometers serve as simple screening devices for the detection of anemia, especially for public health workers in primary health care centers and on the field. Its advantages are as follows -

• Easy portability.

• Battery, as well as mains, operated.

• Faster generation of results (result in 60 seconds).

• Ease of use (no pipetting needed).

• Sensitivity and specificity of digital hemoglobinometers are more accurate.

Limitations of Hemoglobinometers

Some of the commonly reported disadvantages of hemoglobinometers are as follows -

• Abnormal plasma proteins or high leucocyte count cause turbidity interfering in colorimetric readings.

• Color of standardized glass in the comparator box eventually fades over a course of time.

• Individual perspectives in matching the color cause variations in the results.

• The color of the resulting compounds could develop slowly leading to false reporting.

• Some forms of hemoglobins (sulphemoglobin) do not react with the reagents resulting in decreased Hb values.

Conclusion

Hemoglobinometers are simple, quick, and reliable clinical devices for estimating hemoglobin concentration in the blood. They are commonly used in diverse clinical settings such as community hospital settings, private labs, medical institutions, and primary health centers. Hemoglobinometers are the most preferred and cost-effective method for screening the presence of anemia in current clinical practice.