Blood tests are some of the most commonly ordered workups by doctors, either in laboratory or clinical settings. Not only do blood tests help in early diagnosis, but they're also important tools in the assessment of bodily change over time. Blood work can consist of many important tests that track subtle differences in biological markers and help your doctor diagnose many medical conditions. 

Blood tests are routine and some of the most common laboratory procedures. Your doctor might usually order a blood work panel during a routine physical examination, in case he suspects certain underlying causes of disease, or before a major medical procedure. But how often should you get a blood test? We discuss the recommended frequency, general precautions, and the most common bloodwork procedures below.

How Often Should You Get A Blood Test? 

The frequency of your blood work depends on both your health and your doctor's discretion. Blood work consists of a variety of different panels that check for very selective components in your blood, including electrolytes, hormones, and special proteins. Blood tests are ordered by your doctor for three primary reasons: 

• Annual Physical Examination: Your doctor might recommend a blood test during your yearly general physical examination. It gives the doctor a chance to take a closer look at the functioning of your body and catch any warning signs for several medical conditions early on. 
• Underlying Medical Conditions: If you have a complex medical history, and suffer from conditions like obesity, diabetes, heart disease, hypertension, liver and kidney disease, your doctor will recommend more frequent blood tests to monitor your health. Blood work for individuals with underlying conditions can range from every 3 months to every 6 months.
• Sudden Appearance of Symptoms: The onset of symptoms like shortness of breath, fatigue, frequent urination, swelling in the legs and face, all warrant an immediate doctor's appointment. The doctor will order a table of blood tests to make a detailed assessment of your potential condition and eventual diagnosis. 

Be sure to give your doctor a detailed history of your symptoms, medical issues from the past, and also mention your family's medical history. 

What Does Routine Blood Work Look For? 

Blood work contains multiple panels of different tests that look for different components present in your blood and their corresponding levels. Most of the tests that make up a blood panel are important screening tests and are carried out regularly to check for diseases, potential warning signs, and may be required before major medical procedures like surgery. A few common blood tests are:

1. Complete Blood Count

Blood cell counts estimate the numbers of cellular components of your blood - the red blood cells, white blood cells, and platelets. Blood cell counts are extremely commonplace in diagnostic laboratories and hospitals. These tests enable doctors to tell if there's anything wrong with the counts of your blood cells. 

Blood cell counts also measure the quantity of hemoglobin present in your blood. Hemoglobin is the primary pigment in the blood that carries oxygen. Alongside hemoglobin, blood cell counts also indicate hematocrit, or the volume of blood that contains red blood cells. Any abnormal increase or decrease corresponds with underlying health conditions and warrants further testing.  

Here are some common laboratory values for reference: 

• Red Blood Cells: 
• Men - 4.32 - 5.72 million cells/mcL; 
• Women - 3.90 - 5.03 million cells/mcL
• White Blood Cells: 3500 - 9600 cells/mcL
• Platelets: 
• Men - 135,000 - 317,000 cells/mcL; 
• Women - 157,000 - 371,000 cells/mcL
• Haemoglobin: 
• Men - 13.2 - 16.6 g/dL; 
• Women - 11.6 - 15.6 g/dL
• Haematocrit: 
• Men - 38.3 - 48.6%; 
• Women - 35.5 - 44.9%

Please note that the values mentioned here are merely for basic knowledge and reference. All reports must be evaluated only by a registered medical professional. 

2. Metabolic Panel 

This test looks for various chemically active components in your blood that drive your body's metabolism. The main organs involved in your body's metabolism are the kidneys, the spleen, the liver, and the various glands. A metabolic panel is a very specific test that tells your doctor your body's comprehensive chemical status. A metabolic panel looks for - 

• Electrolytes and mineral ions like chloride, potassium, calcium, and sodium. 
• Enzymes and markers secreted by the liver, spleen, glands, and kidneys. 
• Excretory products like urea, ammonia, creatinine. 
• Blood sugar levels and specific proteins that are indicators of organ function. 

The test is highly specific and extremely accurate. Often, many early indicators of disease are detected by observing abnormal values on a metabolic panel. 

Reference ranges and normal values for this test are: 

• Sodium: 136 - 144 mEq/L
• Potassium: 3.7 - 5.2 mEq/L
• Chloride: 96 - 106 mmol/L
• Calcium: 8.5 - 10.2 mg/dL
• Blood Glucose: <100 mg/dL (fasting)
• Carbon Dioxide: 23 - 29 mmol/L
• Blood Urea Nitrogen: 6 - 20 mg/dL
• Creatinine: 0.8 - 1.2 mg/dL
• Alkaline Phosphatase (ALP): 44 - 147 IU/L
• Alanine Aminotransferase (ALT): 7 - 40 IU/L
• Aspartate Aminotransferase (AST): 10 - 34 IU/L
• Bilirubin: 0.3 - 1.9 mg/dL
• Albumin: 3.5 - 5.4 g/dL
• Total Protein: 6 - 8.3 g/dL

3. Blood Sugar Panel 

Blood sugar is an important indicator of conditions like diabetes. Both Type-1 and Type-2 Diabetes screenings include testing for blood sugar levels. This test is included in all routine examinations and is especially highlighted in individuals that are obese, have a sedentary lifestyle, are middle-aged, and/or have a family history of diabetes.

Elevated blood sugar can be caused by the lack of insulin, the resistance of the body's cells to insulin, or a combination of both reasons. This is the primary cause of diabetes. Insulin transports the glucose in your blood to your cells to be used as fuel. In the lack of this hormone, blood sugar accumulates in the blood and can cause a lot of long-term complications such as neuropathy, retinopathy, heart disease, and nephropathy (kidney disease). Blood sugar is measured at three different periods:

• Fasting - Tested on an empty stomach 
• Post Prandial - Tested after a meal 
• Random - Tested during any given time of day

Reference values for blood sugar tests are: 

• Fasting Blood Sugar: <100 mg/dL
• Post Prandial Blood Sugar (After a meal): <180 mg/dL
• Random Blood Sugar: <200 mg/dL

4. Lipid Panel 

There exist freely floating fat droplets in the blood called triglycerides, and complex molecules of fat called cholesterol. The lipid panel measures the level of these molecules in your blood and is an important risk assessor for heart disease. This test is specifically recommended to obese individuals, people with a family history of heart disease, and individuals approaching middle age. The test measures freely floating fat droplets; the triglycerides, high-density lipoprotein (good cholesterol), low-density lipoprotein (bad cholesterol), and very low-density lipoprotein (the component that creates the greatest risk for heart disease). 

Reference values for the lipid panel are: 

• Total Cholesterol: <200 mg/dL
• HDL: 60 mg/dL or higher, risk of heart disease increases if 40mg/ dL or lower
• LDL: <100 mg/ dL
• VLDL: 5 - 40 mg/ dL
• Triglycerides: <150 mg/ dL

5. Coagulation/Clotting Function Panel 

Blood contains several specialized proteins that carry out a complex chain reaction that results in clotting. Blood clots not only prevent loss of blood due to hemorrhage but are also the most important components of the body's healing mechanism. Clots release specific chemicals that signal inflammation in the area and subsequent repair of the injury.

The coagulation panel is a set of tests that determines the speed of your body's clotting factors. A variety of conditions, medications, and predispositions can result in either a quicker or delayed clotting response. A clotting function panel has three primary components: 

• Prothrombin time
• Partial Thromboplastin time
• International Normalized ratio

Any abnormal values can indicate underlying medical conditions and your doctor may call for further testing. A range of normal values for this panel are: 

• PT: 10 - 12 seconds
• PTT: 30 - 45 seconds
• INR: 1 - 2 

6. Thyroid Function Panel 

The thyroid gland is one of the most important glands in the body. Though the gland weighs just about an ounce in adults, it carries out essential functions related to growth, metabolism, and normal body function. The thyroid achieves this by secreting a set of hormones called Tri-iodothyronine (T3) and Thyroxine (T4). The functioning of the thyroid is also determined by a hormone called the thyroid-stimulating hormone, secreted by the pituitary gland. The thyroid panel judges the levels of these three hormones alongside the level of binding of a particular T3-binding protein called thyroxine-binding globulin. The doctor can make further diagnoses based on elevated or reduced levels of these hormones and parameters, and can also order more tests. 

Reference values for this panel are: 

• T4: 4.6 - 12 ug/ dL
• T3: 80 - 180 ng/ dL
• TSH: 0.5 - 6 uU/ mL
• T3RU: 23% - 37%

7. Enzyme Markers Panel

Enzymes are biological catalysts that drive the molecular basis of metabolism and body function. Analyzing the levels of enzymes and any linked abnormalities can help your doctor with a pinpoint diagnosis and a timely treatment plan. The commonly employed enzyme marker panel tests are:

• CPK1: An enzyme found in the brain and lungs. 
• CPK2 & 3, Troponin: Enzymes found in the cardiac muscles. 

Abnormalities in the levels of these enzymes can indicate trauma, cancer, cardiac arrest, and heart attacks. Normal values for these enzymes are- 

• CPK1: 200 U/ L
• CPK2: 5 - 25 IU/ L 
• CPK3: 200 U/ L 
• Troponin: <0.2 ng/ mL

8. DHEA & Sex Hormones Panel 

The production of testosterone dominates in sexually mature men, whereas the production of estrogen dominates in sexually mature women. The two are steroid hormones synthesized by the body following the development of secondary sexual characteristics. Both hormones are synthesized from a hormone called Dehydroepiandrosterone (DHEA). DHEA is secreted by the adrenal gland. Understandably, the levels of DHEA are the highest in young adults and reduce with advancing age. Abnormally high or low levels of DHEA might indicate different conditions in men and women like PCOS, erectile dysfunction, and tumors of the pituitary and adrenal gland.

Reference ranges for DHEA levels are:

• Men: 280 - 640 ug/ dL
• Women: 65 - 380 ug/ dL

9. Sexually Transmitted Diseases

For individuals with multiple sexual partners, it is important to get screened for STDs regularly. Diseases like chlamydia, gonorrhea, syphilis, HIV, herpes, and hepatitis can sometimes remain undetected. Specific testing and screening might be required to detect these diseases. Consider being tested in case you have a new sexual partner as well. Regular screening ensures your own and your partners' safety.

10. C-Reactive Protein Panel 

When the body undergoes inflammation, the liver produces a protein called C-Reactive Protein. It indicates massive trauma, intoxication, poisoning, autoimmune diseases, and heart disease. C-Reactive Protein tests are important in the early diagnosis of serious diseases like those affecting the heart. Elevated C-Reactive Protein indicates a raised risk to the heart. Here are some values for reference- 

• Ideal or Low Risk: <1 mg/ L
• Intermediate Risk: 1 - 2.9 mg/ L
• High Risk: >3 mg/ L
• Very High Risk: >10 mg/ L

How Long Does Blood Work Take? 

Most blood tests take between 24 and 72 hours after sample collection. Though this varies depending on the laboratory and the nature of the tests, this is the median waiting period. Most labs will release your test results directly to your doctor's office or a patient-dedicated web portal. 

What Should You Eat Before Blood Work 

Most doctors recommend you maintain an empty stomach before sample collection. Food can affect parameters like blood sugar, lipids, metabolic panels, and liver function tests. A fasting period of eight hours should suffice. Be sure to schedule your sample collection right before breakfast in the morning to avoid daytime fasting.

The Procedure & Its Importance

The procedure is simple and is performed by a trained phlebotomist, who will sanitize the skin over your vein before collecting the sample. The samples will be collected in a few test tubes based on the number of tests and their requirements. The area of puncture is covered with a sterile bandage or cotton.

Blood work happens to be the most widely performed diagnostic test. The test is commonplace in laboratories, private practices, and hospitals due to its cost-effectiveness, high specificity, and minimally invasive approach. Be sure to contact your healthcare provider for further queries on blood work or in case you think you need a test.