Introduction

The measurement of hemoglobin and hematocrit levels and red blood cell count are among the most common laboratory tests worldwide ¹ because they are essential for the diagnosis and follow-up of hematologic disorders, mainly anemia ², a disease highly related not only to iron deficiency and other nutrient (vitamin B12, folic acid) deficiencies ³ but also, to a lesser extent, to erythrocyte morphology and volume disorders, autoimmune diseases and neoplasia, among other conditions ⁴. Hemoglobin, a complex hemoprotein found inside erythrocytes (although similar globins can also be found in non-erythroid cells ⁵), phylogenetically conserved since the beginning of the evolution of living things (as functionally similar globins can be found in other vertebrates, invertebrates and prokaryotes ⁶), is responsible for transporting oxygen and carbon dioxide, as well as serving as a pH buffer by capturing hydrons when it loses oxygen ⁷. Hematocrit, also known as packed cell volume or erythrocyte volume fraction ⁸, is the volume percentage of red blood cells in blood, so this measurement depends on the number of red blood cells ⁹. Red blood cell count is a test that is part of a complete blood count, measures the number of red blood cells in a blood sample ¹⁰ and is used in routine medical consultations to monitor or diagnose disorders involving decreased or excess red blood cell production ¹¹.

Hemoglobin levels are measured in automated machines where erythrocytes are broken down and hemoglobin is released into a solution so that its concentrations are spectrophotometrically measured using the cyanmethemoglobin method ¹². Hematocrit is not directly measured: the automated system multiplies the number of red blood cells by their mean corpuscular volume ¹³. This fact has led to questioning the relevance of performing both measurements in terms of cost-effectiveness ¹⁴ when the objective is the screening and diagnosis of anemia on a large scale since, as mentioned before, most hemoglobin is contained in red blood cells ¹⁵. Furthermore, previous research studies have suggested that both tests are very highly correlated ¹⁶; likewise, less frequent diseases with significant clinical symptomatology, such as macrocytic anemia and polycythemia, cause disagreement between hemoglobin and hematocrit ¹⁷.

This research aimed to determine the degree of correlation between hemoglobin and hematocrit and between hemoglobin and red blood cell count in apparently healthy patients attending routine medical consultations in the district of Villa El Salvador in Lima, Peru. The results will allow us to determine whether this relationship is strong enough to question the relevance and cost-benefit of requesting a hematocrit test paired with a hemoglobin test, and also to determine the degree of correlation between these parameters and red blood cell count in our population.

Materials and methods

Results

Most patients aged 11 years or younger who attended the polyclinic showed adequate hemoglobin ranges (Table 1).

It was observed that most male patients had adequate hemoglobin ranges (90.2 %) and a relatively high percentage of female patients had inadequate hemoglobin levels (35.1 %) (Table 2).

Spearman’s rank correlation coefficient showed that, in general, making no difference between groups, there was a strong positive correlation between hemoglobin and hematocrit (Rho = 0.928) compared to hemoglobin and red blood cell count (Rho = 0.838). Likewise, a strong positive correlation between hemoglobin and hematocrit was observed in males and females, as well as between hemoglobin and red blood cell count, being this correlation higher in the male group (Table 3).

The correlation between hemoglobin and hematocrit was high and positive in all female age groups; on the other hand, the correlation between hemoglobin and red blood cell count was moderate and positive in the 1-10 and 11-17 year old groups and high in the young adulthood, middle adulthood and older adulthood groups (Table 4).

The correlation analysis according to the male age group showed a high and almost perfect positive correlation in the 1-10 year old group; correlations between hemoglobin and hematocrit and between hemoglobin and red blood cell count were high and positive in all groups except in the 1-10 year old group, in which a moderate and positive correlation between hemoglobin and red blood cell count was found (Table 5).

Discussion

It was observed that a higher percentage of females had lower-than-normal hemoglobin levels than males. The reason for this is that iron deficiency anemia is usually more common in females than in males ¹⁸ because of menstrual losses (which may involve up to 20 mg of iron ¹⁹), pregnancy ²⁰, blood loss such as in abnormal uterine bleeding, among others ²¹. Meanwhile, males are not exposed to these risk factors, with the exception of occult bleeding in the elderly, usually from the gastrointestinal tract ²², as well as disorders involving the intestinal absorption of vitamin B12 ²³.

A high and positive correlation between hemoglobin and hematocrit and between hemoglobin and red blood cell count was found in general and according to sex: specifically, a correlation close to one between hemoglobin and hematocrit. This agrees with a study by Nijboer (2007) that, although focused on establishing the correlation between hemoglobin and hematocrit in patients with different grades of acute blood loss due to trauma, showed that even in these conditions both hemoglobin and hematocrit behaved as almost identical parameters ²⁴. Moreover, although there are studies that question the classic 3:1 hematocrit to hemoglobin ratio ²⁵, the high correlation found in the aforementioned background (acute blood loss) and in the present study (healthy population) shows that they are almost identical parameters; therefore, the systematic use of both tests in preventive-promotional campaigns and screening studies in the general population could be discouraged. A high and positive correlation was also observed between hemoglobin and red blood cell count, which was slightly lower than the relationship between hemoglobin and hematocrit. Even though it could be reasonable to think that a higher correlation should exist because hemoglobin is a hemoprotein found in red blood cells of human beings from the development of the embryonic yolk sac ²⁶, different types of hemoglobin with different affinity for oxygen or carbon dioxide, such as methemoglobin, carboxyhemoglobin, glycated hemoglobin, among others, could slightly decrease the statistical correlation ²⁷.

It was observed that the correlation between hemoglobin and red blood cell count was high and positive in all adult groups of both sexes but moderate in females younger than 18 years and boys younger than 11 years. This agrees with Ahmad (2020), who identified a moderate and positive correlation between hemoglobin and hematocrit in a study aimed at assessing the correlation between blood count variables among children from a school in Rabwah, Pakistan ²⁸. Because hemoglobin is a hemoprotein physiologically bound to red blood cells, it can be stated that increased hemoglobin is related—by yet unclear mechanisms—to a smaller increase in red blood cells among infants, toddlers and children. This could probably be attributed, for example, to the fact that fetal hemoglobin (with shorter life span and oxygen-carrying capacity) is still found in infants, persisting until about 6 months of age ²⁹. In addition, erythrocyte production in early life stages and part of childhood may be considered in almost every bone in the body ³⁰, which could imply a large production of less mature erythrocytes than those of later life stages.

The limitations of this study were the lack of randomization, as patients were selected on a first-come, first-served basis. Moreover, since the study was limited to measuring degrees of correlation, it was not possible to define the presence and types of anemia based on hemoglobin, hematocrit or red blood cell count in the study patients.

In conclusion, hemoglobin levels are positively and highly correlated with hematocrit in males and females of all ages. Likewise, hemoglobin correlates moderately and positively with red blood cell count in females younger than 18 years and boys younger than 11 years. The results suggest that simultaneous hemoglobin and hematocrit testing may be unnecessary in screening and preventive-promotional campaigns on anemia conducted in large population groups. Likewise, with respect to the correlation between hemoglobin and red blood cell count, further research is needed to deepen the reasons why correlation goes from moderate to high in the age groups of both sexes.