Blood Tests For Hypertension
General

Blood Tests For Hypertension – Preparation, Procedure, And Results

Hypertension is one of the most commonly found non-communicable diseases in India as well as all over the world. The prevalence of hypertension in India is considerably high owing to lifestyle changes, low awareness among people, lack of medical facilities and poor control.

What Is Hypertension?

Hypertension can be defined as a systolic blood pressure greater than 140 mm of Hg or diastolic blood pressure greater than 90 mm of Hg.

The diagnosis of hypertension can be ascertained based on an average of two or more readings taken on two or more visits after the first screening.
Hypertension can be differentiated into the following grades based on the systolic and diastolic blood pressure readings

 
Grade Of Hypertension Systolic Blood Pressure (mm of Hg) Diastolic Blood Pressure (mm of Hg)
Grade I (mild) 140 – 159 90 – 99
Grade II (moderate) 160 – 179 100 – 109
Grade III (severe) Greater than 180 Greater than 110
Isolated systolic hypertension Greater than 140 Less than 90

White Coat Hypertension

This is also called as masked hypertension. People having this type of hypertension are generally free from anti-hypertensive medications. These patients do not require any medications since their blood pressure is normal on all occasions except when they visit a doctor, a clinic or a hospital setting.

What Causes Hypertension?

Hypertension can also be divided into two major types depending upon the underlying causes.

Primary Hypertension Secondary Hypertension
This type is also called essential hypertension.

The cause of this type of hypertension is mostly unknown but can also occur due to a combination of genetic and environmental factors.

About 2-3% of all cases of hypertension fall under this category.

Secondary hypertension may occur due to a variety of renal and endocrine factors.

Causes

  • Genetic and hereditary causes
  • Low physical activity or sedentary lifestyle
  • High salt intake
  • Obesity
  • Insulin resistance
  • Low birth weight and intrauterine nutrition
Causes

Renal Causes

  • Glomerulonephritis
  • Diabetic nephropathy
  • Polycystic kidney disease
  • Renal artery stenosis

Endocrine Causes

  • Cushing’s syndrome
  • Pheochromocytoma
  • Thyroid disorders
  • Acromegaly
  • Hyper-parathyroidism

Other Causes

  • Oral contraceptives
  • Glucocorticoids
  • Alcohol
  • Acute stress
  • Pregnancy induced hypertension
  • Coarctation of aorta
  • Abuse of recreational drugs

Signs And Symptoms Of Hypertension

Often, patients may remain asymptomatic and high blood pressure is detected as an accidental when people visit the doctor for screening for some other illness.
However, some of the signs and symptoms associated with high blood pressure may be

  • Dizziness or a sensation of lightheadedness
  • Fainting
  • Palpitations
  • Flushing of face
  • Tinnitus
  • Disturbances in vision

Can A Blood Test Detect High Blood Pressure?

No. High blood pressure can only be detected and monitored using a blood pressure apparatus, also called as the sphygmomanometer.

Why Does Your Doctor Advice You To Undergo Blood Tests For Hypertension?

Once you are diagnosed with hypertension (the basis of diagnosis is mentioned above), your doctor may advise you to undergo certain laboratory tests.
These blood tests do not directly diagnose high blood pressure. But the levels of certain minerals, ions, hormones and certain other blood constituents such as cholesterol help to detect the underlying possible cause for high blood pressure.

Similarly, a CBC for hypertension may also be done as a routine test for the slightest alterations in its parameters also help to diagnose the possible cause.
Subsequently, these parameters may also need to be monitored serially once you are on treatment for high blood pressure. Annual blood tests for hypertension may also be done to monitor response to treatment.

Preparation For The Test

  • Blood tests for hypertension generally do not require any specific preparation except if you are asked to undergo a lipid profile test or a thyroid function test which needs overnight fasting of at least 10-12 hours.
  • Before reporting to the laboratory or the clinician’s office for a blood test for hypertension, it is important to keep yourself well hydrated by drinking plenty of water. This makes it easier for the nurse to find the vein to collect blood sample.
  • Continuation or discontinuation of some regular medications before the test must be ascertained by your doctor.
  • Avoid smoking or consuming alcohol at least 24 hours before the test as these may interfere with test results.

Procedure Of The Test

  • Blood test for hypertension requires collection of blood through a vein, mostly at the flexor portion of the elbow.
  • The nurse will apply a tourniquet above the site from where blood has to be collected.
  • The skin overlying the vein is cleaned and made sterile with alcohol.
  • A needle is inserted into the vein and the desired amount of blood is collected into vials.
  • The tourniquet is then loosened and a small cotton swab is placed over the vene-puncture site to prevent blood from oozing out. You will be required to apply slight pressure over the swab for about 10-15 minutes until the bleeding stops.
  • Since no major procedure is carried out, you will be able to resume work or return to your regular routine immediately after the blood is collected.

Interpretation Of Results

Interpretation of results will depend upon the type of blood test done for hypertension. Some blood tests with their normal parameters are mentioned below.

Blood Glucose Levels

Condition Fasting (mg/dl) Postprandial (mg/dl)
Normal 80 – 100 120 – 140
Pre-diabetic 101 – 125 140 – 160
Diabetic Greater than 126 Greater than 200

Apart from blood glucose levels, HbA1c (glycosylated hemoglobin) test is also done which gives the patient’s percentage value of average blood sugar over the last 3 months.

Lipid Profile Test

Parameter Optimal Borderline High
Total cholesterol 

(mg/dl)

<200 200 – 239 >239
LDL cholesterol 

(mg/dl)

<130 130 – 159 >159
HDL cholesterol 

(mg/dl)

<60 40 – 60 <40
Triglycerides 

(mg/dl)

<150 150 – 199 >199

Complete Blood Count (CBC)

Parameter Normal Range
Hemoglobin (males) 13 – 16 gm%
Hemoglobin (females) 12 – 14 gm%
White blood cells (WBC) 5000 – 10000 cu/mm of blood
Red blood cells (RBCs) 4.5 – 5.5 million/ml
Platelets 1.5 – 5.0 lakhs/ml
Mean corpuscular volume (MCV) 80 – 94 fl
Mean corpuscular hemoglobin (MCH) 27 – 32 pg
Mean corpuscular hemoglobin concentration (MCHC) 28 – 36 g/100ml of red blood cells
Lymphocytes 850 – 4100 cells/ml
Monocytes 200 – 1100 cells/ml
Neutrophils 1500 – 7800 cells/ml
Eosinophils 50 – 550 cells/ml
Basophils 0 – 200 cells/ml

Serum Electrolytes

Parameter Normal Range
Sodium (mEq/L) 135 – 145
Potassium (mEq/L) 3.5 – 5.0
Chloride (mEq/L) 96 – 109
Calcium (mg/dl) 8.5 – 10.5
Magnesium (mEq/L) 1.4 – 2.1
Phosphorus (mg/dl) 3 – 4.5

Thyroid Function Test

Parameter Normal Range
T3 0.92 – 2.78 nmol/L
T4 58 – 140 nmol/L
TSH 0.5 – 4.7 mU/L

Kidney Function Test

Parameter Normal Range
Blood urea nitrogen (BUN) 5 – 25 mg/dl
Creatinine 0.3 – 1.4 mg/dl

Blood tests for hypertension are generally done annually to either diagnose or to monitor the response to treatment for hypertension. Yet, you must consult the doctor if you notice any abnormalities in the test results even if they are done as a routine screening.

Leave a Reply

Your email address will not be published. Required fields are marked *