Blood tests are part of regular health checks. However, sometimes interpreting the results becomes confusing due to terms that are unknown and normality values reflected in different ways. In addition, two aspects have to be taken into account: the values of the determinations are not always expressed in the same units and the “normal” figures may have small variations , since they depend on the laboratory that analyzes the sample. This article describes some of the determinations that are made in a routine blood test , although it is always better to rely on the criteria of the health professional before being alarmed at a result that is not understood. They are also giventhe indications that must be followed before an analysis .
Analysis of blood cells: the blood count
The three groups of cells present in the blood are: red blood cells , white blood cells and platelets. Red blood cells, also called red blood cells, are the corpuscles (elements) responsible for transporting oxygen from the lungs to all cells of the body. Inside is hemoglobin, which carries oxygen and is responsible for the characteristic red color of blood.
Before a blood test, it is recommended not to exercise hard, not to smoke and avoid a copious dinner
Analyzes reflect various values of red blood cells. First, it is common to see the number of red blood cells , expressed in millions per cubic millimeter, whose normal values vary between 4.300.000 and 5.900.000 / mL. Hemoglobin also quantifies hemoglobin (between 12.5 and 17 g / L), which is often proportional to red blood cells; that is, when there is anemia , both the number of red blood cells and the number of hemoglobin are low. The hematocrit is the percentage of red blood cells in the total blood volume and is also a good indicator for anemias. Acceptable results are different in men, from 40.7% to 50.3%, than in women, from 36.1% to 44.3%.
In the blood count, other useful data are available: VCM (Mean Corpuscular Volume, with values between 78 and 100 femtolter, fL), which reflects the size of red blood cells; HCM (Mean Corpuscular Hemoglobin, ranging from 27 to 32 picograms per cell, pg / cell), based on the amount of hemoglobin in each hematocyte; and CHCM (Mean Corpuscular Hemoglobin Concentration, 32 to 36 gm / dL), which relates the amount of hemoglobin that carries the red cell to its volume.
For the white blood cells or leukocytes , the blood count reflects its total number (it consists of the word “count”, with normal values between 3,500 and 11,000 / mL) and the different classes of leukocytes (collected as “leucocyte formula”). Leukocytes are the basic pillar of defense against microorganisms. There are several types and each of them is responsible for a specific function: neutrophils, lymphocytes, monocytes and eosinophils.
The number of leukocytes increases in infections and predominates one type or another, depending on the type of microorganisms ( bacterial infections increase neutrophils and those caused by viruses, lymphocytes and monocytes). They may decrease in very serious infections, in diseases of the bone marrow or as a side effect of some drug.
Finally, the blood count studies platelets (130,000 and 450,000 / mL), involved in the formation of blood clots. Hematologic diseases and liver disorders are the most frequent causes that alter their number.
Study of liver and kidney function: biochemistry
The determinations related to the kidney are urea (normal value: 10 and 40 mg / dl), creatinine (between 0.6 and 1.2 mg / dl) and the ionogram. The creatinine is a muscle protein that circulates in the blood and is excreted through the urine. Their levels are one of the most accurate indicators of kidney function. Urea also measures renal function and degree of hydration. It increases in renal insufficiency , dehydration states and in individuals with a lot of muscle mass.
Transaminases with values above normal denote that there is a process that causes an inflammation
Since one of the primary functions of the kidney is the elimination of water and electrolytes, the study of renal function is complemented by the ionogram, which determines the levels of sodium, potassium and chlorine . The latter are sometimes identified by the acronyms of the periodic table of elements: Na (135-146 mEq / l), K (3.5-5.0 mEq / l) and Cl (98-106 mEq / l) ), respectively.
In the section of the biochemistry also the function of the liver is studied. Values shown as GOT / ALT (normal value between 0 and 37 U / L), GPT / AST (between 0 and 41 U / L) and GGT (between 11 and 50 U / L) correspond to what is known as transaminases. They are enzymes that are found inside the liver cells. Values above normal denote that there is a process that causes inflammation. These processes may be as varied as hepatitis (acute or chronic) or the toxic effects of alcohol or certain drugs .
Alkaline phosphatase is another enzyme that is present in the liver as well as pregnant in other areas such as bone, and its value ranges from 40 to 129 U / L. It tends to arise in problems of obstruction of the bile ducts and in some alterations of the bone, like in the phase of consolidation of a fracture or in infiltrations tumor. Often, children have high numbers of alkaline phosphatase during the growth stage.
Alkaline phosphatase and bilirubin levels (0.2 mg / dL and 1 mg / dL) are also indicators of liver health . Bilirubin is formed by destroying hemoglobin and is taken up by the liver, which eliminates it by bile. When it is not able to metabolize it properly (as in various liver diseases) or when there is a problem in the excretion of bile (such as stones in the gallbladder), high levels of bilirubin are detected. If they are important, a very characteristic yellowish skin dye is known as jaundice.
Metabolism study: glucose and cholesterol
Glucose is a sugar (carbohydrate) , as the main source of energy for cells. Their levels vary during the day and are maximum in the two hours that follow the ingestion and minimums after prolonged fastings. Normal levels range from 70 milligrams per deciliter of blood (mg / dL) to 110 mg / dL. The diagnosis of diabetes is established when there are two fasting determinations above 126 mg / dL or one above 200 mg / dL, even after a meal.
High LDL, responsible for transporting cholesterol to tissues, contributes to the deposition of more cholesterol in the walls of the arteries
In the case of blood glucose values above 100mg / dL, but below 126mg / dL, glucose intolerance is indicated, which may indicate a previous state of diabetes . In these cases, it is recommended to perform a glucose overload study: it consists of administering a preparation with 75 g of glucose and determining the glycemia at two hours. If values between 140 and 199 are obtained, the diagnosis of diabetes is also established .
For the study of fats or lipids , analytics determine cholesterolvaluesand triglycerides. Cholesterol studies their total levels and some of their fractions, which are known as “good” cholesterol (HDL) and “bad” cholesterol (LDL). Cholesterol is an essential element for life, since it is the precursor of some hormones and bile acids. Since it is a fatty substance, it is not soluble in blood water and needs a lipoprotein to transport it. The best known lipoproteins are LDL and HDL. LDL is responsible for the transport of cholesterol to tissues, so if it is high, it contributes to the deposition of more cholesterol in the walls of the arteries. In contrast, HDL removes cholesterol from tissues and, for that reason, is popularly known as “good” cholesterol .
The interpretation of the results that appear in the analytic can give rise to confusions since, contrary to what happens with the glycemia, there are no values of “normality” that are accepted for the whole world, but they are in function of each person and depend on their cardiovascular risk. This means that the same cholesterol levels are not recommended for a person who has had a heart attack rather than a healthy, non-smoker.
As a guide, people who have had a cardiovascular problem (stroke, stroke …) should keep total cholesterol below 200 mg / dl and the LDL fraction between 70-100 mg / dl (or 2.58 mmol / l). Conversely, if the cardiovascular risk is low, it is sufficient that LDL levels below 130 mg / dl are maintained. The triglycerides correspond to the fat that we ingest with the diet. They increase with diets high in fat and in people with overweight or with significant alcohol intake. Values below 150 mg / dL are recommended.