Blood tests: Understanding the different kinds

Written By: Dr Anitha Anchan | Updated : April 22, 2015 3:35 PM IST

There seem to be scores of hard-to-pronounce, harder-to-remember blood tests that doctors seem to order every time you visit them. So many, that you don't know if they are actually needed or whether the doc is just messing around with you. Thankfully, Dr Anitha Anchan agreed to dumb things down for us mere mortals and explain the different kinds of blood tests - what they are called, why they are necessary and what the test results signify:

Complete Blood Count (CBC) Test

The most routine blood test out there it gives information about the cells in your blood. A complete blood count will include various investigations. Abnormally high or low counts can indicate the presence of anaemia, infections, clotting problems, blood cancers and immune system disorders. To read more about the CBC test, click here.

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Erythrocyte Sedimentation Rate (ESR)

It is the rate at which red blood cells settle down when the blood is place in a tube under specified conditions in an hour. It is a nonspecific test because increased results do not show where the inflammation is and what is causing it. The rate tends to be higher among women especially during menstruation and pregnancy. Drugs such as dextran, methyldopa, oral contraceptives and theophylline can increase ESR.

High ESR values are seen in acute and chronic inflammations, infections, cancers and autoimmune diseases. ESR value decreases in congestive heart failure, hypofibrinogenemia, polycythaemia and sickle cell anaemia. Drugs like aspirin, cortisone, and quinine may also decrease ESR.

	Normal values of ESR (Westergren method)
Males	0-15mm/hour
Females	0-20mm/hour
Children	0-10mm/hour

Blood Cultures

Blood cultures are commonly done when infection is suspected. It is a test to detect the presence of microorganisms like bacteria and fungi in the blood. The sample is placed in a culture media, it is then incubated in a controlled environment and observed for growth in the microorganisms. 2-3 blood cultures are usually done before the result is considered negative.

Blood Typing and Cross-matching

A blood typing test is used to identify blood group. The Blood group is determined by two special proteins (antigens), the ABO antigen and the Rhesus antigen.

Cross matching is the process that is done prior to a blood transfusion to test compatibility of the donor and the intended recipient. It is important that anyone who receives blood is given blood that matches their blood group to prevent the immune system from attacking the red blood cells. Cross matching is also used during pregnancy as there is a small risk that the unborn child may have a different blood group from the mother.

Blood Glucose test

It is used todiagnose and monitor diabetes. Glucose is a type of sugar that the body uses for energy. People with diabetes often have high levels of glucose in their blood.

Routine blood glucosetests are done at any time with no preparation. The normal range is 80 to 110 mg/dL. Shortly after eating, the blood glucose level may rise temporarily up to 140 mg/dL. With repeated tests, a glucose level greater than 200 mg/dL may indicate diabetes.
A postprandial glucose test determines the amount of glucose in the blood after a meal. A 2-hour postprandial blood sugar measures blood glucose exactly 2 hours after eating a meal. By then blood sugar usually goes back down in healthy people, but it may still be elevated in people with diabetes. Diabetes is present if the amount of blood-sugar two hours after a meal is greater than 200 mg% on two separate occasions. Blood-sugar values between 140 and 200 mg% is termed 'impaired glucose tolerance'.
For pre-prandial (fasting) blood glucose tests, you should not eat anything for several hours before the test. Normal fasting blood sugar is between 90 and 130 mg/dL. Diagnosis of diabetes is made when two separate blood tests show your fasting blood glucose level greater than or equal to 140 mg/dL.

Home Blood Sugar Testing - A blood glucose meter is an electronic device for measuring the blood glucose at home. The blood glucose test is performed by pricking your finger with a small, sharp needle (lancet), putting a drop of blood on a chemically active disposable test strip and then placing the strip into a digital meter that displays your blood sugar level. Within few seconds, the blood glucose level will be shown on the digital display.

Lipoprotein Panel

It is a blood test to show whether you're at risk for coronary heart disease (CHD). It measures the levels of LDL and HDL cholesterol and triglycerides in your blood. You may need to fast for 9 to 12 hours before a lipoprotein panel.

	Values	Inference
Total cholesterol	< 200 mg/dL	Desirable
Total cholesterol	240 mg/dL and above	High
*LDL (bad) cholesterol* (main source of cholesterol build-up and blockages in the arteries)	< 100 mg/dL	Optimal
	160 189 mg/dL	High
*HDL (good) cholesterol* (helps decrease blockages in the arteries)	< 40 mg/dL	Major risk factor for heart disease
	60 mg/dL and above	Considered protective against heart disease
Triglycerides (can also raise heart disease risk)	< 150mg/dL	Normal
	150-199mg/dL	Borderline high
	> 200mg/dL	High

Enzyme-linked Immunosorbent Assay (ELISA) test

Your immune system produces specific antibodies in response to infections (such as HIV) or allergy (such as peanut allergy). An ELISA test checks for the associated antibody in the blood.

Blood test for Sexually Transmitted Diseases

Some viral sexually transmitted diseases are screened by drawing blood samples. Blood tests for STD include testing for the following diseases:

HIV/AIDS - blood drawn three to six months after possible exposure can detect HIV antibodies
Hepatitis B - blood examined for antibodies.
Syphilis - test done three months after possible exposure can detect antibodies
Herpes - blood examined for antibodies; however, many standard tests are not accurate
Chlamydia
Gonorrhoea

Western Blot

It is the confirmatory HIV test. The period of time between HIV infection and the appearance of anti-HIV antibodies in the blood is called the window period. During this period the test result is negative. This test is also used for screening people in high-risk groups, pregnant women, organ donors and blood donors.

Liver Function Tests

When the liver is damaged, it releases enzymes into the blood and levels of proteins produced by the liver decreases. The test measures the levels of these enzymes and proteins. It is used to help diagnose certain liver conditions, such as hepatitis (liver infection), cirrhosis (liver scarring) and alcoholic liver disease (liver damage caused by excessive alcohol consumption).

Genetic Tests

Gene test - Polymerase chain reaction (DNA Testing) - A gene test is used when a specific genetic mutation is suspected to be responsible for a person's symptoms. DNA is extracted from your blood sample and searched for the suspected genetic mutation. Genetic conditions that can be diagnosed using a gene test include - Haemophilia: blood's ability to clot (thicken) affected; Cystic fibrosis: build-up of sticky mucus in the lungs; Sickle cell anaemia: shortage of normal red blood cells and Polycystic kidney disease: cysts inside the kidneys.
Chromosome testing (Karyotyping) - It is a more general test which is used when a person's symptoms are suspected to be caused by a gene-related problem but the specific gene is not known.Chromosome testing is often used to test children with physical or developmental problems without any apparent cause and for couples who have experienced repeated miscarriages.
Genetic Screening - Similar to gene testing, but it is used in people who have no obvious symptoms. Genetic screening is carried out during pregnancy (antenatal screening) to check for common genetic conditions, such as Down's syndrome (extra genetic material causes delays in the mental and physical development of a child), Sickle cell anemia and Thalassemia. It is also done with people who are thought to be at risk of developing a genetic condition like Huntington's disease (a disorder in which nerve cells in certain parts of the brain degenerate).

Calcium and Electrolyte levels in blood serum

Calcium is an important mineral present in the body. Electrolytes are minerals like sodium, chloride, bicarbonate and potassium, which help maintain fluid levels and acid-base balance in the body. Normal values of minerals are:

	Values	Indication
Calcium	8.4 - 10.2 mEq/dl	Abnormal levels may be a sign of kidney problems, bone disease, thyroid disease, cancer, malnutrition, etc
Sodium	136-145 mEq/L	Increases(hypernatremia) in dehydration, kidney disease or persistent diarrhoea.Decreases (hyponatremia) in poorly controlled diabetes, liver disease, lack of sodium in your diet or pneumonia.
Potassium	3.5 - 5.0 mEq/L	Increases (hyperkalemia) in kidney failure and ACE inhibitor (to treat high blood pressure) medication.Decreases (hypokalemia) as a result of heavy sweating or persistent vomiting or diarrhoea.
Chloride	95-105 mEq/L	Increases(hyperchloremia) in certain kidney diseases, diarrhoea or overactive parathyroid glands.Decreases (hypochloremia) as a result of heavy sweating, vomiting and some types of kidney disease.

Protein Electrophoresis

This test measures specific proteins in the blood to help identify diseases. Different elements of a blood serum are separated into individual components like albumin and globulin (alpha1, alpha2, beta and gamma) proteins. The test is used to screen variety of diseases like multiple myeloma (plasma cell cancer), macroglobulinemia, amyloidosis (group of diseases that result from the abnormal deposition of amyloid protein in various tissues of the body), liver dysfunction and chronic fluid-retaining conditions and to find the cause of hypogammaglobulinemia (HGG).

Protein	Normal values
Albumin	38-50g/L
Alpha-1 Globulin	1-3g/L
Alpha-2 Globulin	6-10g/L
Beta Globulin	7-14g/L
Gamma Globulin	7-16g/L

Blood Urea Nitrogen (BUN) and Creatinine

Blood tests for kidney function measure levels of blood urea nitrogen (BUN) and creatinine which are waste products filtered out of the body by the kidneys. Abnormal BUN and creatinine levels may be signs of a kidney disease.

Blood enzyme tests used to check Troponin and Creatine

Troponin and creatine tests are ordered when patients have chest pain or other heart attack signs and symptoms. Troponin is a muscle protein which leaks out into your blood when muscle or heart cells are injured. A blood product called Creatine Kinase-MB (muscle brain) is released when the heart muscle is damaged.

Northern Blot (RNA testing)

It is a technique for identifying specific sequences of RNA. It is used in cancer research and genetic identification between species. It can be used to observe a particular gene's expression pattern in infection, over the course of treatment, in the rejection of transplanted organ, etc. Northern blot analysis has also been used to detect cancerous pancreatic cells and tissues.

Whew! Hopefully, we've managed to cover most of the major blood tests and what they mean. If you've any further doubts and queries please ask us on our Q and A section.

Read more about causes, symptoms, diagnosis and treatment of hiv/aids.

Also read: Blood tests: Understanding the basics

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