Blood tests serve as valuable diagnostic tools, providing healthcare professionals with insights into a person’s health status. These tests measure various components in the blood, offering clues about organ function, the presence of disease, and overall well-being. However, the accuracy of these results can be influenced by several factors, one of which is the body’s hydration level. Dehydration can significantly alter blood test outcomes, potentially leading to misinterpretations and inaccurate diagnoses.
How Dehydration Alters Blood Composition
Dehydration directly impacts plasma, the liquid portion of blood. When the body loses more fluid than it takes in, total blood volume decreases due to a reduction in plasma volume. This reduction in plasma leads to hemoconcentration, where the cellular and dissolved components become more concentrated. Substances like red blood cells, electrolytes, proteins, and waste products are packed into a smaller volume, causing their measured levels to appear falsely elevated. These changes are temporary and reversible with proper rehydration.
Specific Blood Tests Impacted
Dehydration can significantly affect the results of several common blood tests. For example, a Complete Blood Count (CBC) often shows falsely elevated levels of hematocrit and hemoglobin. Hematocrit measures the percentage of red blood cells in the blood, and when plasma volume decreases due to dehydration, the red blood cells become more concentrated, artificially raising this percentage.
Electrolyte levels, including sodium, potassium, and chloride, can also be affected; their concentrations often appear higher due to reduced water content. Kidney function tests, such as Blood Urea Nitrogen (BUN) and creatinine, frequently show elevated levels when a person is dehydrated. This occurs because reduced blood flow to the kidneys, a consequence of dehydration, can temporarily impair their ability to filter waste, leading to a higher BUN-to-creatinine ratio that suggests kidney stress rather than actual damage.
Glucose levels might appear falsely elevated because the blood’s concentration makes the existing sugar more prominent. Liver function test parameters, particularly albumin, can also show increased concentrations. Albumin, a protein made by the liver, becomes more concentrated in the blood when fluid volume is reduced.
Ensuring Accurate Results Through Hydration
To ensure accurate blood test results, proper hydration before a blood draw is advised. Drinking sufficient plain water in the hours leading up to a test helps maintain normal blood volume, preventing artificial concentration of blood components. This practice aids in obtaining reliable test results and can also make the blood draw process smoother, as well-hydrated veins are typically easier for healthcare professionals to locate and access.
Unless specific fasting instructions prohibit it, general guidelines suggest consuming about 8 ounces of water approximately one hour before a blood test, and maintaining good hydration in the 24 hours prior. Communicate any concerns about hydration or symptoms of dehydration to the healthcare provider or phlebotomist before the test. This transparency allows them to interpret results more accurately and determine if retesting after proper hydration is necessary, preventing potential misdiagnoses or unnecessary follow-up procedures.