Have a patient with variations in their Hemoglobin (Hb) and Hematocrit (Hct)? Then consider the patient’s hydration status. Hemoglobin and hematocrit are measures of the amount of red blood cells in circulation, with Hb measuring the amount of oxygen-carrying protein in the blood and Hct measuring the percentage of blood volume made up of red blood cells. Both Hb and Hct can be affected by changes in blood volume, which can occur due to changes in hydration status.

Dehydration can cause an increase in both Hb and Hct levels, as a result of a decrease in plasma volume. Conversely, overhydration or fluid overload can cause a decrease in Hb and Hct levels, as a result of an increase in plasma volume. It is important to consider the patient’s hydration status when interpreting Hb and Hct levels, as well as any other relevant patient history or laboratory findings.

In addition to hydration status, other factors that can affect Hb and Hct levels include underlying medical conditions such as anemia, bleeding disorders, and chronic kidney disease, as well as certain medications (testosterone) and lifestyle factors such as smoking and alcohol use.

Overall, it is important to consider these factors in the context of the patient’s overall clinical picture, and to repeat Hb and Hct measurements as needed to monitor changes over time. I will typically recheck it in a week if the numbers don’t make sense. Sometimes, it is just a lab error!