What are the urinalysis (UA) findings indicative of dehydration?

From the Guidelines

Dehydration is best indicated by serum or plasma osmolality >300 mOsm/kg, rather than relying solely on urinalysis findings. When evaluating urinalysis for dehydration, one should consider the following findings:

• Increased urine specific gravity (>1.025)
• Decreased urine volume
• Darker yellow or amber coloration
• Increased urine osmolality (>800 mOsm/kg)
• Elevated urine sodium concentration
• Higher urine creatinine level
• Presence of ketones in cases of severe dehydration
• Variable urine pH, potentially more acidic 1. However, it's crucial to note that these urinalysis findings should be interpreted in conjunction with clinical correlation and other signs of dehydration, such as decreased skin turgor, dry mucous membranes, and thirst 1. The most recent and highest quality study suggests that serum osmolality is the primary indicator of hydration status, and an action threshold of >300 mOsm/kg should be used to identify low-intake dehydration in older adults 1.

From the Research

Urinalysis Findings Indicative of Dehydration

To assess dehydration through urinalysis (UA), several factors can be considered:

• Urine specific gravity (USG): A value of ⩾1.013 can indicate dehydration with high accuracy 2
• Urine color: A subject-assessed urine color of ⩾4 can offer high sensitivity and moderate specificity for detecting dehydration 2
• Urine osmolality: A value of >500 mOsm/kg can be indicative of dehydration 2, 3, 4, 5

Limitations of Urinalysis in Dehydration Assessment

However, it's essential to note that:

• The diagnostic accuracy of urinary measures, including USG, urine color, and urine osmolality, may be limited in certain populations, such as older adults 3, 6
• Physical signs and urine markers may show little utility in determining hydration status in elderly patients 6
• Saliva osmolality has demonstrated superior diagnostic accuracy compared to physical signs and urine markers in assessing dehydration in older individuals 6

Additional Considerations

Other factors that can influence urinalysis findings include:

• Changes in body weight, haematological parameters, and bioelectrical impedance can also be used to assess hydration status 4
• Urine color can be a reasonable indicator of hydration when laboratory analysis is not available or when a quick estimate is necessary 4, 5