How Does Dehydration Affect Blood Tests and Lab Results?

Dehydration is one of several factors that should be considered when inaccurate blood test results are suspected. Water accounts for approximately 60% of an adult human’s body weight, and impacts virtually every system in the body—including the circulatory system. Which blood tests are most commonly affected by dehydration? Learn more below.

Can dehydration skew a cholesterol test?

Yes, it is possible for dehydration to skew the results of a cholesterol test. This is attributed to the fact that dehydration can cause blood volume to decrease, leading to a drop in blood pressure and blood flow. When this occurs, it increases the risk of cholesterol accumulation in the arteries. Additionally, the body may increase production of cholesterol in response to severe dehydration, in order to protect cell membranes. 

Can dehydration affect an electrolyte test?

Yes. Electrolytes are minerals found in body tissues and fluids in the form of dissolved salts, and are responsible for maintaining a healthy water balance. A typical electrolyte panel measures sodium, potassium, chloride, and bicarbonate. Any condition that affects the amount of fluid in the body—including dehydration—can cause an electrolyte imbalance. 

Can dehydration affect a kidney values test?

Yes. Two of the most common tests for evaluating kidney function and diagnosing kidney disease are the blood urea nitrogen (BUN) test and creatinine test. Both tests measure the amount of waste product in the blood; higher volumes of BUN and creatinine indicate that the kidneys are not working properly. Dehydration is known to reduce blood flow to the kidneys and elevate creatinine and BUN levels in the blood.

Can dehydration skew a CBC test?

Possibly. A complete blood count (CBC) test evaluates the overall health of the blood cells circulating in the body. Hematocrit is one component of the CBC test that can be skewed as a result of dehydration. This test measures the proportion of blood that is made up of red blood cells (RBCs); as the volume of fluid in the blood drops, the proportion of RBCs rises. 

Humans get about 20% of the water we need to sustain our bodies from the foods we eat, so fasting can increase the risk of dehydration. If your doctor recommends fasting before a blood test, be sure to drink enough water leading up to the test to help ensure accurate results.