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Blood Tests

Blood  tests in the laboratory detect any disturbances in the chemical levels of your body. There are several tests done, each for its specific purpose:

  • Haemogram: For detailed assessment of vital parameters of blood

  • Blood Group: Essential for donating or receiving blood in case of emergencies

  • Urine test (Routine & Micro): For detecting infections or any other abnormality in the kidneys and urinary tract

  • Blood sugar For detecting blood sugar levels. Essential in detecting diabetes

  • Blood Urea & Serum Creatinine: For assessing the performance of the kidneys

  • SGPT, SGOT, Serum Bilirubin: For assessing the performance of the liver

  • Lipid profile: For analysis of the good and bad cholesterol levels in your blood as they are an excellent indicator of the condition of your heart

  • Thyroid Stimulating Hormone (TSH): For assessing the functioning of thyroid gland

  • Australia Antigen: For detecting the presence of Hepatitis B

  • Vitamin B 12: For assessing the levels as it plays a key role in the normal functioning of the brain, nervous system and in the formation of blood.

    How it is done?

    You will be made to sit on a chair with your arm on the hand-rest of the chair or on a table. The technician will insert the needle in a particular vein of your arm and draw in a small quantity of blood, which will then be sent to a lab for testing.

Method of testing

Normal ranges


Test results are usually interpreted based on their relation to a reference range.

The "Normal" or Reference Range

"Your test was out of the normal range," your doctor says to you, handing you a sheet of paper with a set of test results, numbers on a page. Your heart starts to race in fear that you are really sick. But what does this statement mean, "Out of the normal range"? Is it cause for concern? The brief answer is that a result out of the normal range is a signal that further investigation is needed.

The interpretation of any clinical laboratory test involves an important concept in comparing the patient's results to the test's "reference range." (It's also commonly called the "normal range" but today reference range is considered a more descriptive term.


What is a reference range?

Some tests provide a simple yes or no answer.

A typical lab report will have your results followed by a normal or reference range. For example, your results for a thyroid-stimulating hormone (TSH) test might look something like: 2.0 m-IU/L, ref range 0.5 - 5.0 m-IU/L. The test results indicate that it falls within the "normal" range.

How was that reference range established? The short answer is: by testing a large number of healthy people and observing what appears to be "normal" for them.


Effects of Age and Sex on the reference range

For many tests, there is no single reference range that applies to everyone because the tests performed may be affected by the age and sex of the patient, as well as many other considerations.

Alkaline phosphatase is an enzyme found in the cells that make bone, so its concentration in the body rises in proportion to new bone cell production. In a child or adolescent, a high alkaline phosphatase level is not only normal but also desirable-the child should be growing healthy bones. But these same levels found in an adult are a sign of trouble-osteoporosis, metastatic bone disease (extra bone growth associated with tumors ), or other conditions. So experience from testing large numbers of people has led to different reference ranges by age group.

Haemoglobin and hematocrit (a red blood cell measure) both decline as a natural part of the aging process.

The patient's sex is another important consideration for many tests.

Creatinine is produced as a natural by-product of muscle activity and then removed from your bloodstream by your kidneys. Because males have greater muscle mass than females, the reference range for males is higher than for females.

As another example, blood loss through menstruation may cause lower haemoglobin and hematocrit levels in premenopausal women.


Other Factors Affecting Test Results

Laboratories will generally report your test results accompanied by a reference range keyed to your age and sex. Your physician then will still need to interpret the results based on personal knowledge of your particulars, including any medications or herbal remedies you may be taking. Additional factors that can affect your test results include your intake of caffeine, tobacco, alcohol, and vitamin C; your diet (vegetarian vs. non-vegetarian); stress or anxiety; or a pregnancy. Even your posture when the sample is taken can affect some results, as can recent heavy exertion.

It's important to comply with your doctor's instructions in preparing for the test, such as coming in first thing in the morning, before you eat anything, to get your blood drawn. That compliance makes your sample as close as possible to others; it keeps you within the parameters of your reference group.


What does it mean if my test result is out of the reference range?

Based on the laws of probability, 1 out of 20 (or 5%) determinations will fall outside the established reference range, thus a single test value may mean nothing significant. Generally, the test value is only slightly higher or lower than the reference range. To put this in more perspective: If a doctor runs 20 different tests on you, there's a good chance that one result will fall out of a reference range despite the fact that you are in good health.

Of course, the result may indicate a problem. The first thing your doctor is likely to do is to re-run the test. Perhaps the analyte being measured happened to be high that day due to one of the reasons stated above, or perhaps something went awry with the sample (the blood specimen was not refrigerated, or the serum was not separated from the red cells, or it was exposed to heat).

Laboratories will generally report the findings based on age and sex, and leave it to the physician to interpret the results based on factors such as diet, your level of activity, or medications you are taking.

If you know of any special circumstances that could affect a test, mention them to your doctor; don't assume your doctor has thought of every possible circumstance.


Sample type

Fasting type

Why do you need to fast prior to some blood tests?

What will happen if you do not fast before getting tested for blood sugar or cholesterol?

Your doctor might have told you to undergo a blood test and specified that you should fast for at least 10 hours before going for one. You might think that chewing mint after your dinner or sipping a cup of coffee in the morning is ok. But in reality, fasting for less than 10 – 12 hours can affect your test results


Why is fasting before certain blood tests necessary?

Fasting means you should not eat/drink any food or drinks, except water for a set period because the nutrients present in food are absorbed into your bloodstream, which in turn affect the parameters being measured.


What will happen if you don’t fast for a set period?

The time required for fasting (before going for a blood test) is calculated based on the overall rate of metabolism in a healthy individual, which is around 10-12 hours prior to having your blood drawn. If you don’t fast, or fast for a less than the prescribed duration, your test results might be inaccurate. This means that you might have to repeat the test for a proper diagnosis.

Also, some test values change may change depending on the type of food you eat. For example, if you eat lots of sweets, your blood sugar will be high. Hence, to avoid inaccurate readings and improper diagnosis, follow your doctor’s instructions without fail.


What other activities or foods you should refrain from before going for a blood test?

In most cases, it is recommended not to drink any juice, tea or coffee, prior to getting tested. However, you may have a few sips of water. Also, do not smoke, chew gum or exercise as these activities may stimulate the digestive system and affect the test results.


What is the best time for a blood test if you are fasting?

You should get your blood test done in the early morning as it minimizes the length of time you need to go without food. Also, in case of diabetes, post-lunch (after eating) blood test is also carried out to determine the changes in your blood sugar levels. Here are 3 tests for diabetes you should know about.

 Can you take medicines/nutrient supplements before getting tested?

Ask your doctor if you should continue taking your regular medicines/vitamin and mineral supplements while you are fasting. In some cases, these medications might affect the test leading to an inaccurate diagnosis.

 What to do after your blood test is done?

As you are on an empty stomach for more than 12 hours, you might be feeling low on energy. So carry a biscuit packet or a fruit and a bottle of water with you while going for a blood test to satiate your hunger pangs.