Understanding Lab Tests for Dehydration
Written by Private MD Labs Medical Writing Team • Last Updated: September 8, 2025
Dehydration occurs when the body loses more fluids than it takes in, leading to an insufficient amount of water and electrolytes for normal bodily functions. While dehydration is typically diagnosed through clinical assessment and symptoms, blood and urine tests are fundamental for evaluating the severity of fluid loss and monitoring the body's response to dehydration.
Top Recommended Test
Comprehensive Metabolic Profile (includes eGFR)
This comprehensive panel can reveal elevated chloride levels and other electrolyte imbalances that indicate dehydration. It provides a complete picture of how fluid loss affects your body's chemical balance and kidney function.
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Why Lab Testing is Important for Dehydration
Although there isn't a single blood test to directly diagnose dehydration, laboratory testing plays a crucial role in assessing the impact of fluid loss on your body's systems. When dehydrated, blood becomes more concentrated, affecting various lab values and potentially indicating complications that require medical attention.
Other Relevant Tests
Complete Blood Count / CBC (includes Differential and Platelets)
High hematocrit levels can indicate dehydration, as the blood can become more concentrated if the body loses too much water. This test helps assess the concentration of blood cells relative to plasma volume.
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Kidney Function Profile
An elevated BUN to creatinine ratio can indicate dehydration, as water loss can lead to an increase in blood urea nitrogen levels relative to creatinine. This test specifically monitors how dehydration affects kidney function.
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Urinalysis, Complete Profile
This test can detect concentrated urine, amorphous sediment, and hyaline casts - all indicators of dehydration. Dark, concentrated urine is often one of the first laboratory signs of insufficient fluid intake.
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Creatinine, Serum
Elevated creatinine levels can indicate severe dehydration. When the body is dehydrated, the kidneys may not be able to properly process creatinine, leading to increased blood levels.
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Potassium, Serum
Dehydration can cause high potassium levels because of the reduced amount of water in the body, resulting in a higher concentration of potassium in the blood.
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Albumin
High levels of albumin may indicate dehydration, as the amount of fluid in your blood can affect albumin levels. This protein becomes more concentrated when blood volume decreases.
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Urea Nitrogen (BUN)
When a person is dehydrated, the BUN level may rise as blood becomes more concentrated and less able to carry away urea. This is a key marker for assessing dehydration severity.
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Understanding Your Results
Dehydration affects multiple body systems, which is why several different lab values may be elevated or altered. These changes reflect the body's attempt to conserve water and maintain essential functions. The pattern of results, rather than any single test, helps healthcare providers assess the degree of dehydration and guide appropriate treatment.
Important Considerations
The information here is for educational purposes only and is not a substitute for professional medical advice. Severe dehydration can be a medical emergency requiring immediate treatment. Always consult with a healthcare provider for proper diagnosis and treatment of dehydration and related complications.
