Dehydration and Mean Platelet Volume (MPV)
Dehydration typically causes an elevated MPV rather than a low MPV, as it leads to hemoconcentration of blood components. 1
Relationship Between Dehydration and MPV
Dehydration affects laboratory values through hemoconcentration, which typically results in:
- Elevated serum protein levels
- Increased blood cell concentration
- Higher MPV values (not lower)
Physiological Explanation
When examining the relationship between hydration status and platelet parameters:
- Dehydration causes hemoconcentration, which typically increases MPV rather than decreasing it 1
- Research shows that MPV values have a positive correlation with serum creatinine and proteinuria, which are often elevated in dehydration 2
- Plasma osmolality changes associated with dehydration (>300 mOsm/kg indicating definitive dehydration) tend to affect platelet parameters in the direction of elevation 1, 3
Causes of Low MPV
Low MPV is more commonly associated with:
- Certain inflammatory conditions
- Specific hematological disorders
- Bone marrow suppression
- Some medications
Rather than being caused by dehydration, low MPV may be seen in:
- Patients with emphysema (1.92 times higher odds of having MPV < 10th percentile) 4
- Certain demographic groups (males, age 45-64 years, and those with recent hospital stays) 4
Clinical Assessment of Dehydration
When evaluating hydration status:
- Serum osmolality is the gold standard for determining dehydration (>300 mOsm/kg indicates definitive dehydration) 1, 3
- Urine specific gravity >1.020 and body mass changes >1% suggest dehydration 1
- Clinical signs include dry mucous membranes and decreased skin turgor 1
Management Implications
For accurate laboratory interpretation in suspected dehydration:
- Consider hydration status before attributing abnormal laboratory values to pathological conditions 1
- Rehydrate patients before retesting laboratory values to avoid misinterpretation 1
- For mild to moderate dehydration, provide oral rehydration with 6 mL of water per kg of body mass every 2-3 hours 1
Common Pitfalls
- Confusing "dehydration" with "hypovolemia" - these terms are often incorrectly used interchangeably 3
- Attributing laboratory abnormalities to disease processes without considering hydration status 1
- Failing to recognize that dehydration typically causes elevated (not decreased) MPV values 1, 2
- Not accounting for the complex relationship between hydration status and hemostatic parameters 5
In summary, while dehydration affects multiple laboratory parameters, it typically causes an increase in MPV rather than a decrease. Low MPV values should prompt investigation for other causes beyond hydration status.