04-06-2021 / Health and Fitness

Dehydration Affects Blood Pressure and Lab Blood Test Results

When inaccurate blood test results are suspected, dehydration is one of the several factors that should be considered. Here are the effects of dehydration on blood pressure and common blood tests

Dehydration Affects Blood Pressure and Lab Blood Test Results
Mazia AhmedMazia Ahmed

Mazia Ahmed

MSc Nutrition Science, Ph.D. Scholar

Topic of Content


A reduction of the central circulating blood volume in addition to dehydration results in stroke, a fall in cardiac blood pressure, and a fall in cardiac output, if left uncompensated. Dehydration can be serious and can cause serious and threatening complications like kidney problems and heart-related emergencies if left untreated. Not only does it cause kidney problems or heart-related issues, but in addition to this, dehydration can also cause potentially dangerous changes in blood pressure.

The most common reason for dehydration include poor oral intake of water and fluid loss from-

  • Skin, for example, fever and burn

  • The gastrointestinal tract, for example, vomit and diarrhea

  • Urine for example diabetes insipidus, diabetes ketoacidosis, glucosuria and diuretic therapy.

Causes of Dehydration

There are several other possible causes of dehydration other than not drinking enough fluids. The following causes include-

  • Illness- Vomiting and diarrhea can lead to a significant loss of fluid and electrolytes along with a high fever causing dehydration.

  • Increased sweating- Water is lost when you are sweating, so an increase in sweating can occur in hot weather or during exercises or sick with a fever, thus leading to dehydration.

  • Frequent urination- You can also lose fluid through urination while taking medications like diuretics or having underline conditions such as alcohol consumption or diabetes that causes frequent urination resulting in dehydration.

Clinical Features of Dehydration

  • Dry skin

  • Dry mucus membrane

  • Reduce skin turgor

  • Orthostatic hypotension

  • Reduce axillary sweating

  • Cognitive impairment

  • Tachycardia and hypertension

  • High osmolality and concentrated urine

  • Reduced urinary output

  • Feeling fatigued or tired

  • Dizziness and lightheadedness

  • Confusion

  • Dark-colored urine

Dehydration Symptoms

Symptoms of Dehydration in Children

  • Absence of tears when crying

  • Irritability

  • Sunken eyes, cheeks, or soft spot on the skull

  • No wet diapers for several hours

  • Fatigue

Biochemical Changes Due to Dehydration

  • Raised creatinine

  • Raised serum urea

  • Increased urea and creatinine ratio

  • Reduced estimated glomerular filtration rate

  • Hyponatremia

  • Raised urine specific gravity

  • Raised serum or urine osmolality

  • Dehydration affecting your blood pressure

Effects of Dehydration on Blood Pressure

Blood pressure is the amount of force your blood exerts on the walls of your veins and arteries, and due to dehydration, there can be an effect on your blood pressure, causing it to rise up or down.

1. Dehydration and Low Blood Pressure

When your blood pressure reading is lower than 90/60 mm Hg, it results in low pressure, where dehydration can cause low blood pressure due to a decrease in blood volume. To adequately reach all the tissues of your body, maintaining a normal blood volume is necessary for blood. Therefore, when you are dehydrated, your blood volume can decrease, resulting in a drop in blood pressure. Thus, your organs won't receive the nutrition and oxygen they need when blood pressure drops too low and can potentially result in shock.

2. Dehydration and High Blood Pressure

High blood pressure happens when the systolic reading of blood pressure is 140 mm Hg or higher and the diastolic reading is more than 90 mm Hg. There is a link between high pressure and dehydration because dehydration can increase blood pressure due to the actions of a hormone called vasopressin secreted when there's a higher amount of solute in the blood or when the blood volume is low. Your kidney absorbs water, but dehydration opposes urine from passing. Moreover, when you are dehydrated and high concentration of vasopressin can also cause your blood vessels to constrict, leading to increased blood pressure.

Dehydration Dangers

9 Effects of Dehydration on Hematocrit

Hematocrit is the volume of Red Blood Cells (RBCs) in the blood. Dehydration is the most common cause of a high hematocrit value because the volume of the fluid in the blood drops and the red blood cells per volume of blood rises, thus causing inaccurate results of the test. But with adequate intake of fluid, the hematocrit returns to normal.

1. Effect of Dehydration on Hemoglobin

If a person is severely dehydrated, the hemoglobin will appear higher than the patient with normal blood volume. Also, if the patient's fluid is overloaded, the hemoglobin range will be lower than their actual level. This is because hemoglobin and hematocrit are based on whole blood volume and therefore are dependent on plasma volume.

2. Effect of dehydration on CBG measurement

Dehydration causes hypertension and increases glucose utilization in the local tissues. Thus this leads to the false low result of the capillary blood glucose (CBG) test.

3. Effect of Dehydration on Blood Glucose

The rise in glucose was found to be out of proportion to changes in metabolite concentrations that could be due to passive concentration of the plasma (haemoconcentration) as a result of dehydration. Also, an increase in hepatic glucose production, with increased plasma glucose levels during hyperosmolality can be caused by dehydration.

4. Effect of Dehydration on Renal Function Test

Dehydration has multiple effects on the kidney. The loss of body water leads to an increase in serum osmolality and activation of vasopressin which results in urinary concentration.

5. Effect of Dehydration on Liver Function Test

There is a significant difference in serum total albumin and protein level in a dehydrated patient before and after hydration with intravenous fluid. Still, the liver enzymes and bilirubin level remain unchanged, indicating the change in protein level due to dehydration status rather than a liver abnormality.

Keep yourself hydrated for Healthy Kidney

6. Effect of Dehydration on Lipid Profile

There has been an investigation carried out in fasting subjects to see dehydration on lipid profile. The subjects were allowed to fast firstly with no fluid replacement and then with salt and water supplements where the fasting subjects with no fluid has higher total serum cholesterol, LDL cholesterol, HDL cholesterol, apolipoprotein A1 and apolipoprotein B compared to the subject who had fasted with salt supplements and prior fluids.

7. Effect of Dehydration in Cholesterol Test

Dehydration causes blood volume to decrease, leading to a drop in blood pressure and blood flow, resulting in cholesterol accumulation in the arteries. To protect cell membranes, the body may increase the production of cholesterol in response to severe dehydration.

8. Effect of Dehydration in a Lab Blood test and Blood pressure

Due to dehydration, there can be inaccurate blood test results as suspected, as water accounts for approximately 60% of the adult human body weight. So, lack of water may lead to dehydration and thus affecting blood pressure and blood test results.

9. Effect of Dehydration in Kidney Value Test

Two of the most common tests for diagnosing kidney diseases and evaluating kidney functions are the creatinine test and the blood urea nitrogen (BUN) test. Higher volumes of BUN and creatinine indicate that the kidney is not working properly as the test measures the amount of waste product in the blood. Dehydration can reduce the blood flow to the kidney and can elevate the blood urea nitrogen level and creatinine level in the blood.

Word of Wisdom

Thus, dehydration can be dangerous and threatening if not treated in time and can hamper the status of the patient and the laboratory results. So before any routine blood test, a patient should avoid unnecessary hot, dry environments, physical activities, and diuretic substances such as caffeine and ensure adequate water intake.


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