From the Guidelines
Dehydration can be indicated on a Complete Blood Count (CBC) by an elevated hematocrit level, which is the most significant indicator, as well as increased hemoglobin levels, elevated red blood cell (RBC) count, and increased mean corpuscular hemoglobin concentration (MCHC). When dehydrated, blood becomes more concentrated, causing these values to rise above normal ranges. The white blood cell count can sometimes show a mild elevation due to hemoconcentration, though this is less specific 1. These changes occur because dehydration reduces plasma volume while the number of blood cells remains constant, creating a relative increase in cellular components. It's essential to interpret these CBC changes alongside clinical symptoms and other laboratory findings, as similar patterns can appear in other conditions like polycythemia. Rehydration typically reverses these CBC abnormalities within hours to days, depending on severity. Some key points to consider when evaluating dehydration through a CBC include:
- Elevated hematocrit levels, typically above 45% in men and 42% in women
- Increased hemoglobin levels
- Elevated RBC count
- Increased MCHC
- Possible mild elevation in white blood cell count due to hemoconcentration It's crucial to note that while these indicators can suggest dehydration, they should be considered in conjunction with clinical presentation and other diagnostic findings, as they can also be present in other conditions. The provided evidence does not directly link the management of chronic myeloid leukemia 1 to the signs of dehydration on a CBC, but it does emphasize the importance of hydration in various medical contexts. In contrast, the ESPEN guideline on clinical nutrition and hydration in geriatrics 1 discusses the challenges of assessing and managing dehydration, particularly in older adults, but does not specifically address CBC findings in dehydration. However, it highlights the importance of considering dehydration in the context of overall patient care and the need for a comprehensive approach to diagnosis and treatment.
From the Research
Signs of Dehydration on a Complete Blood Count (CBC)
Dehydration can be indicated by several signs on a Complete Blood Count (CBC) report. These signs include:
- Elevated hemoglobin and hematocrit levels: Dehydration can cause a relative increase in the concentration of red blood cells, resulting in higher hemoglobin and hematocrit values 2, 3.
- Increased red blood cell count: Dehydration can also lead to an increase in the red blood cell count, as the body tries to conserve water and concentrate the blood 3.
- Changes in blood urea nitrogen (BUN) and creatinine levels: While not directly measured on a CBC, dehydration can affect kidney function, leading to changes in BUN and creatinine levels, which can be measured on other blood tests 4.
Effects of Dehydration on Blood Parameters
Studies have shown that dehydration can affect various blood parameters, including:
- Hemoglobin and hematocrit levels: A study published in the Southern Medical Journal found that saline bolus infusion can cause a significant decrease in hemoglobin and hematocrit levels, but these parameters tend to return to baseline over time 3.
- Urinary excretion: Dehydration can inhibit urinary excretion, as the body tries to conserve water 2.
- Electrolyte levels: Dehydration can also affect electrolyte levels, including sodium and chloride, which can be measured on other blood tests 4.
Clinical Implications
In clinical practice, the signs of dehydration on a CBC can be used to guide treatment and management of patients with dehydration. For example:
- A study published in the Indian Pediatrics journal found that children with acute diarrhea and severe dehydration who received Ringer's lactate solution had improved outcomes compared to those who received normal saline 4.
- Another study published in the New England Journal of Medicine found that the use of lactated Ringer's solution versus normal saline did not result in a significantly lower incidence of death or readmission to the hospital within 90 days after the index admission 5.