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Tests to diagnose and monitor high blood pressure

Various tests to diagnose high blood pressure, evaluate organ damage and monitor antihypertensive drug therapy.

Blood pressure (BP) is one of the critically important vital signs of life. It is the force exerted by circulating blood on the walls of the blood vessel as the heart pumps blood. It is expressed as systolic/diastolic blood pressure. Maximum pressure in the arteries as the ventricles of the heart contracts and pushes blood out is called the systolic blood pressure (SBP). A normal systolic blood pressure is 120 mm Hg or below. The pressure in the arteries as the heart muscle relaxes following its contraction is called diastolic blood pressure (DBP). Normal diastolic blood pressure ranges between 60 and 80 mm Hg.

Latest JNC guidelines of hypertension

According to the new guidelines by the Eighth Joint National Committee:

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  • The definition of high blood pressure remains the same under the new guidelines. Hypertension is a blood pressure above 140/90.
  • The normal range of blood pressure revised from 140/90 to 150/90 for people above 60 years of age. Medication in adults aged 60 or older is recommended only when their blood pressure exceeds 150/90.
  • Diabetics and kidney patients younger than 60, like everyone else that age be treated when their blood pressure exceeds 140/90. According to previous guidelines, treatment was to be initiated in such patients when their blood pressure reading surpassed 130/80.

Tests to diagnose hypertension

The only way to know whether you have hypertension is to by measuring your blood pressure. Blood pressure is measured with an instrument called sphygmomanometer. The diagnosis needs to be confirmed at a recall visit one to four weeks later.

Normal BP: 120 mmHg/80 mmHg.

Prehypertension: SBP 120-139 and DBP 80-89

Hypertension: SBP 140 or higher and DBP 90 or higher

Isolated diastolic hypertension: only DBP is above normal

Secondary hypertension results from an underlying condition like diabetes, kidney disease, thyroid problems, blocking of arteries, pheochromocytoma, adrenal disease, heavy alcohol intake, etc. Depending on your physical examination and medical history, specific tests like urinalysis, electrolyte panel, lipid profile, fasting glucose, HbA1C, blood TSH and T4 tests, blood urea nitrogen and creatinine tests, etc. may be ordered to help detect the possible underlying conditions. Blood levels of sodium and potassium are checked to exclude hypertension resulting from adrenal disease. Cholesterol profiles are used to assess cardiovascular risk and glucose levels are tested to evaluate diabetes. Thyroid disorder is diagnosed by measuring thyroid stimulating hormone levels. Likewise, blood urea and creatinine measurements are measured to exclude kidney disease as a secondary cause of hypertension [1].

Tests for organ damage

Hypertension is known as a silent killer. High and uncontrolled blood pressure can damage your arteries, nerves, eyes, heart, kidneys and brain. Damage to organs due to uncontrolled hypertension is called end-organ damage. Your doctor may order different tests to assess any organ damage from high blood pressure. Diagnosing hypertensive end organ damage early can help reverse it with specific and aggressive treatment.

EYES

Eye examination with an ophthalmoscope is done to look for changes in the retina at the back of the eyes. It looks for swelling or damage of the eye nerve, bleeding in the retina, narrowing of the small arteries of the eyes, etc.

HEART AND BLOOD VESSELS

A full cardiovascular assessment is conducted if you have persistently raised blood pressure.

1. Lipid profile

A lipid profile can assess the risk of developing atherosclerosis. The test evaluates the levels of total cholesterol, HDL cholesterol, LDL cholesterol and triglycerides. LDL, the bad cholesterol , tends to deposit blood cholesterol on the arterial walls.

LDL values and inference: < 100 mg/dL is optimal

100-129 mg/dL is above optimal

130-160 mg/dL is borderline high

> 160 mg/dLis high

High blood LDL levels cause the formation of clots (plaques) in the blood vessels and cause narrowing of the vessels.

HDL values and inference: HDL value of 60 mg/dL and above is considered protective against heart disease.

< 40 mg/dL in men and < 50 mg/dL in women is a major risk factor for heart disease.

Triglyceride values and inference: < 150 mg/dL is normal

150-199 mg/dL is borderline high

200-499 mg/dL is high

> 500 mg/dL is very high

Hypertriglyceridemia, or high levels of triglycerides, is a risk factor for coronary artery disease and other heart diseases.

Very low-density lipoprotein (VLDL) values and inference: 2-30mg/dL is normal

VLDL has the highest quantity of triglycerides and hence increased levels contribute to heart disease.

Total cholesterol values and inferences: < 200mg/dL in adults and <170 mg/dL in children is desirable

200-240mg/dL in adults and 170-200mg/dL in children is borderline high

> 240mg/dL in adults and >200mg/dL in children is high

Total cholesterol/HDL ratio: 3.0 is desirable

5.0 is borderline

6.0 is high risk

The lower the total cholesterol level, the better it is for the heart.

2. Pulse wave velocity

It is the rate at which blood pressure waves (arterial pulse) move down the blood vessel. It is usually measured between the major blood vessel supplying blood to your brain (carotid artery) and main blood vessel of the leg (femoral artery). Normal PWV: 5-10 m/s in people below 50 years of age and 6-12 m/s in people above 50 years of age. Depending on the device used, values above 10 to 12 m/sec are classified as pathological (disease causing)2. A raised pulse wave velocity suggests an increased risk of death from conditions of the heart or blood vessels.

3. Chest X-ray

A chest X-ray can evaluate and provide an estimate of the size of the enlarged heart muscle. It is less specific than the detailed echocardiography.

4. Electrocardiogram

Electrocardiography or ECG measures the electrical signals that travel through the heart and records it on paper in the form of a graph showing waves in a distinct pattern. Depending on the shape of these waves, doctors can evaluate any abnormal condition of heart. The test helps determine heart rate, rhythm, conduction abnormalities, left ventricular size and look for evidence of damage to specific regions of the heart muscle.

5. Echocardiography

An echocardiogram is an ultrasound examination of the heart. The test might be considered to confirm or refute the presence of left ventricular hypertrophy or LVH (enlargement of the heart muscle) suggested by ECG findings [2]. It is the gold standard for diagnosing hypertensive heart disease. It most accurately evaluates LVH, which may be a precursor of angina (chest pain due to obstructed blood supply to the heart muscle), arrhythmia (abnormal heart rhythm), heart failure, and dyspnea (breathlessness). It can also determine contraction and relaxation function of the left ventricle, as well as the size of the left atrium.

6. Doppler ultrasound

It checks blood flow through the arteries. It can help detect peripheral vascular disease.

KIDNEY

Urea and creatinine are the gold standard markers to detect kidney disease. Kidney abnormalities due to high blood pressure (hypertensive nephropathy) can be detected by using kidney function tests which measure the levels of these markers.

1. Serum creatinine

Normal range: Males - 0.8 to 1.2mg/dL and Females - 0.6 to 0.9mg/dL

Higher levels may indicate kidneys dysfunction. The levels increase as the kidney disease progresses.

2. Protein (albumin) in urine

Proteins are typically not detectable in urine. An abnormal quantity of the protein albumin in the urine (albuminuria) could be an early sign of kidney disease [2].

5-30 mg/dL - Trace

30 mg/dL - 1+

100 mg/dL - 2+

300 mg/dL - 3+

>1000 mg/dL - 4+

3. Blood urea nitrogen (BUN)

Normal range: 7 to 20 mg/dL

Higher levels (greater than 20-40 mg/dL) may be suggestive of altered kidney function.

4. eGFR

Since serum creatinine alone is not a reliable measure of kidney function, eGFR is recommended as an index of kidney function2.

90-120 ml/min/1.73 m2: Normal range

60 and 89 mL/min/1.73m2: mild chronic kidney disease (CKD)

30 and 59 mL/min/1.73m2: moderate CKD

15-29 mL/min/1.73m2: Severe CKD

<15 mL/min/1.73m2: kidney failure (dialysis needed)

THYROID

Thyroid dysfunction is detected and monitored by thyroid function tests which measure the levels of thyroid-stimulating hormone (TSH), triiodothyronine (T3) and thyroxine (T4) in the blood.

1. Thyroid Stimulating Hormone (TSH)

Measuring the TSH can help early detection of thyroid dysfunction.

Normal range: 0.4 to 4.0 milli-international units per liter of blood (mIU/L)

Lower values indicate overactive thyroid (hyperthyroidism) and higher values indicate underactive thyroid (hypothyroidism).

2. Free T4

Normal range: 9 - 25 picomoles/litre

Lower values indicate hypothyroidism and higher values indicate hyperthyroidism.

3. Free T3

T3 level assessment helps diagnose and determine the severity of thyroid dysfunction.

Normal range: 3.5 to 7.8 pmol/litres

A low T3 level indicates hypothyroidism and a high T3 level indicates hyperthyroidism.

Tests to monitor medications

Your doctor may order different tests to monitor for side effects of antihypertensive medications and assess any organ damage from them. Blood potassium and creatinine tests may be ordered to monitor therapy with ACE inhibitor, Angiotensin II receptor blockers (ARB), diuretics and aldosterone antagonists.

References

1. National Clinical Guideline Centre (UK). Hypertension: The Clinical Management of Primary Hypertension in Adults: Update of Clinical Guidelines 18 and 34 [Internet]. London: Royal College of Physicians (UK); 2011 Aug. (NICE Clinical Guidelines, No. 127.) 8, Assessing cardiovascular risk, target organ damage and secondary causes of hypertension. Available from: https://www.ncbi.nlm.nih.gov/books/NBK83281/

2. Schmieder, R. E. (2010). End Organ Damage In Hypertension. Deutsches rzteblatt International, 107(49), 866 873. http://doi.org/10.3238/arztebl.2010.0866

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