Diagnostic tests

A list of such diagnostic tests that certainly constitute a part of every day Biology and is being ordinarily expected by the UPSC from a graduate, who intends to take a shot at the civil services, may be stated as below:

Blood-sugar test: As the sugar that is present in our blood in a dissolved state mainly, as Glucose is essentially all that constitutes a universal source of energy for our body to be in a living state. This sugar serves as a fuel which the inbuilt cellular machinery burns in a process called respiration to derive the useful energy out of it. Infact, whatever we consume as food is eventually converted into the sugar and hence, the presence of sugar in the blood is but a natural process and our body has a complete mechanism in place to preserve the sugar as reserve fuel whatever that remains in excess of body’s immediate requirement and thus, an ideal equilibrium is maintained so far as the concentration of sugar in the blood is concerned. Once this equilibrium is disturbed, the ideal sugar level in the blood is thus, not maintained and hence, a diseased condition results what we call as Diabetes that has far reaching consequences on the overall health of an individual which does include the malfunctioning of various other vital organs of the body. Given thus, it necessarily calls for a need to regularly monitor the sugar level of the blood so that a bigger, irreversible damage to the body could be prevented before it gets too late.

In order to monitor the blood sugar level, a specialized diagnostic test is performed what we call as blood sugar test. For performing this test, a blood sample is taken, into which a chemical called as Fluoride-oxalate mixture is added just to prevent the coagulation or normal clotting of the blood besides preventing the RBC’s from consuming the glucose. This is how, the blood sugar is determined as against the ideal value of blood sugar level present in the body. In case, the given sample shows a sugar level higher than the ideal value, it will simply indicate a condition of hyperglycemia and hence, a possible rise of a disease called as Diabetes mellitus. The normal or ideal range of blood sugar per 100 ml or deciliter of blood during fasting, designated as FBS (Fasting blood sugar) and after meals, designated as PP (Post prandial) is as given below:

Blood-haemoglobin test: As we know, haemoglobin is a red colored, iron containing pigment present inside the RBC that not only imparts a red colour to the human blood, but acts as the most important agent of oxygen transport and is thus, described as the respiratory pigment. A reduction in the amount of this pigment from the standard and ideal value of 12-14 gm per 100 ml of blood in an individual shall indicate a condition of anaemia that again can have serious repercussions on the health of an individual.

The amount of haemoglobin in a given sample of blood is measured with the help of an instrument called as Sahli’s haemoglobinometer or Haemometer. In this diagnostic test, the haemoglobin is converted into acid haematin by adding HCl into it. The normal range of Hb.per 100 ml or per deciliter of the blood in an adult human being & children is as given below in the table:

Note: Although, the Hb.content in children per deciliter of blood is less, but the affinity of this Hb. for oxygen is much higher as compared to adults.

Noted further that a single RBC can contain as much as about 280 million Hb.molecules that as such constitutes about 33% of the RBC. It being a conjugated protein is made up of a protein called as Globin and a haem group that is made up of four Porphyrin rings as does a chlorophyll molecule. Structurally, haemoglobin particularly, the globin protein part, is made up of four polypeptide chains, designated as two alpha and two beta chains. While alpha chains are made up of a total of 141 amino acids each and each beta chain is made up of a total of 146 amino acids.

Erythrocytic sedimentation Rate (ESR): A very significant diagnostic test, performed in Cancer patients in which ESR is always on the higher side as compared to normal individuals. ESR does rise in some acute and chronic infections such as TB and other inflammatory diseases although, in normal conditions, ESR also rises in pregnancy. ESR is determined after mixing the blood with an anti-coagulant in which the blood is allowed to stand in a tube. As it stands, the RBC’s start piling up one above the other and hence, settle down in the tube, to which we call as Rouleaux phenomenon. The rate at which the RBC’s settle down in an hour (always calculated in the first hour) and so called as sedimentation, determines the ESR of an individual. The normal range of ESR (Sedimentation in the first hour) is as given below in the table:

Total Leucocyte Count (TLC): The leucocytes or WBC are remarkable blood cells that support the defence mechanism of the body and hence, maintain the immune system of the body. They are also described as the scavenger cells, for they do remove the dead or foreign material (antigen) out of the body through a process called as phagocytosis. Their number is also fixed in the blood and hence, their increase or decrease in number may show different states of the body. An increase in the leucocyte count is called as Leucocytosis; whereas, their decreased count in the blood is called as Leucopenia. The normal range of TLC per cubic millimeter (mm3) of blood is given in the table below:

However, under following conditions, the leucocyte count can also increase to an abnormally high level, as is shown in the table below:

Blood Urea: Urea, the main excretory waste in human beings or for that matter, in all Ureotelic organisms, It is synthesized in the Liver through a cyclic process what we call as Krebs-Hansleit cycle or Ornithine cycle. From the blood, the same is filtered out by the Kidneys else, its presence in the blood beyond permissible levels can be fatal for an individual. If the concentration of urea in the blood increases beyond the normal range, it simply points out at a renal trouble that may end up eventually into a complete renal or kidney failure. Given thus, in order to know about the actual state of health of kidneys, the blood urea test certainly becomes a matter of paramount importance. The amount of urea in the blood is estimated from the amount of Ammonia that liberates following the action of an enzyme, urease on it.

The normal value of Blood-urea is 20-40 mg/100 ml. of blood. This value may increase in Kidney failure cases or dehydration that causes the loss of body fluids. It however, decreases in pregnancy.

Lipid Profile test: Although, lipids are quite essential for the body as being the reservoirs of stored energy and thus, constitute the energy depots of our body. Therefore, they are as much a significant part of our daily diet as do the other components such as carbohydrates and proteins. But what makes the real difference is the quantity and the kind of lipids being consumed by us. Hence, a regular lipid profile of our body becomes a necessary health imperative since, a kind of lipids if found beyond their permissible limits in our body can become a cause of some serious heart ailments. The lipid concentration in our blood is found in the blood plasma where their total concentration is between the range of 400-600 mg per 100 ml. Therefore, it is the profile of the plasma lipids that is generally done to know their actual concentration in the body.

The plasma lipid profile includes the three main components:

• Cholesterol profile (Their normal value in pasma is 1/3^rd of the total plasma lipids (400-600 mg/100 ml) that is equal to 150-220mg/100 ml.

• Triglycerides profile (Their value is also 1/3^rd of the total plasma lipids and hence, comes out to about 150-200 mg.)

• Phospholipids profile (Also 1/3^rd of the total plasma lipid)

The respective value of all three above components in blood plasma is given herein below in the tabulated form:

Notably, the cholesterol is mainly synthesized in the Liver and intestines from where it is carried in the form of lipoproteins. Thus, it is essentially, the determination of these lipoprotein concentrations that is tested in a lipid profile. For the purposes of a lipid profile, following 2-main form of lipoproteins are very significant especially from the view point of their being behind a number of cardiac disorders, so called as CAD (coronary artery disorders or diseases):

?HDL (High Density Lipoproteins): HDL plays a significant role in removing the cholesterol from the plasma as well as the cells and thus, carries the same over to liver. This is why; HDL is described as good cholesterol. Given thus, it is anti-atherogenic in nature and prevents as such so called cardiac disorders. To learn and memorize about which cholesterol is good or bad for health, a simple clue may be taken from H alphabet of HDL and remembered as H for healthy or happy.

?LDL (Low density Lipoproteins): LDL on the other hand, does the other way round and hence, transports cholesterol from the liver to the tissues and thus, increases the cholesterol level in the body particularly, in the cells and plasma. As such, it is directly related to the incidences of cardiovascular diseases. For this reason, it is generally described as the bad cholesterol and is generally associated with promoting clot formation (thrombus) in the heart blood vessels. It can also be remembered by correlating alphabet L of LDL to Lethal.

Given below is the tabulated form of HDL and LDL concentration in the body that must be ideal and the ranges below (for HDL) and above (for LDL) which it can be risky for the body in either case:

ELISA- test

ELISA, an acronym for Enzyme linked Immuno Sorbent Assay, is a quantitative technique for the detection of antigens and antibodies in the blood of a person especially, the one who is suspected to have caught the AIDS infection. In this technique, the most popular enzyme used is called as Alkaline Phosphotase or Peroxidases. These enzymes are linked to either the antigens or antibodies as a label which can then be detected by measuring the enzymic activity. Today, ELISA test is being used for the detection or diagnosis of the following kinds of suspected infections such as:

• AIDS
• STDs *(sexually transmitted diseases)
• Rubella virus
• Hepatitis
• Thyroid disorders and
• hCG etc.

However, besides ELISA, other diagnostic tests being increasingly used in the medical diagnostics today are DNA-hybridization and PCR (Polymerase chain reaction) etc…