Yes, a high red blood cell (RBC) count can be temporary. Dehydration can reduce the fluid in your blood, making red cells appear more concentrated, and living at high altitude can also affect the count. But a high result may also reflect ongoing red blood cell production or another health condition. A clinician may recommend repeat testing and review other results to understand the cause.
An RBC count is usually measured as part of a complete blood count (CBC). One result marked higher than expected does not necessarily mean that your body is producing too many red blood cells. The reason for the result, changes over time, and other blood measurements help determine whether the finding is temporary or needs further investigation.
Why can a high RBC count be temporary?
One important explanation is a change in the balance between red blood cells and the liquid part of the blood, called plasma. When plasma decreases, red blood cells become more concentrated in a blood sample even though the body has not necessarily produced additional cells. This is sometimes called relative or apparent erythrocytosis. According to Mayo Clinic, dehydration and certain medicines that increase fluid loss can cause this type of elevation.
Dehydration and fluid loss
Dehydration is a common reason for a temporarily concentrated blood result. It can occur when the body loses more fluid than it takes in. Situations that may contribute include:
- Vomiting or diarrhea that causes fluid loss.
- Heavy sweating, particularly when fluids are not adequately replaced.
- Not drinking enough fluids during an illness or period of increased fluid needs.
- Taking diuretic medicines, sometimes called water pills, which increase the amount of fluid passed in urine.
When dehydration is responsible, the apparent elevation may improve after the fluid imbalance has been addressed. However, a high RBC result should not automatically be attributed to dehydration without considering other findings. Drink fluids according to your usual needs and any medical instructions you have received; do not deliberately drink excessive amounts of water or stop prescribed medicines to change a test result.
Living at high altitude
At high altitude, the body is exposed to lower oxygen availability. In response, it may increase red blood cell production to help carry oxygen to tissues. The MedlinePlus Medical Encyclopedia notes that the RBC count can increase for several weeks at higher altitudes. Therefore, a change associated with altitude may last longer than a brief episode of dehydration. Recent travel, a move to a higher elevation, or living at altitude can help a clinician interpret the finding.
When might a high RBC count not be temporary?
A high result can also occur when the body continues to make more red blood cells than usual. In these situations, the increase may persist until the underlying cause is identified and managed. The cause is not always serious, but persistent results deserve attention because some conditions require treatment or monitoring.
- Low oxygen levels: Certain lung or heart conditions may reduce the oxygen available to the body and stimulate additional red blood cell production.
- Sleep apnea: Repeated interruptions in breathing during sleep can contribute to lower oxygen levels and a higher RBC count.
- Smoking: Exposure to carbon monoxide from smoking can interfere with oxygen delivery and contribute to an increased red blood cell count.
- Medicines and hormones: Testosterone, anabolic steroids, and erythropoietin used in certain circumstances can increase red blood cell production.
- Kidney-related conditions: Some kidney problems can affect the production of erythropoietin, a hormone that signals the bone marrow to make red blood cells.
- Bone marrow disorders: Polycythemia vera is an uncommon condition in which the bone marrow produces too many red blood cells.
The NHS guidance on erythrocytosis distinguishes between an apparent increase caused by reduced plasma and an absolute increase involving additional red blood cells. This distinction matters because correcting dehydration may address an apparent elevation, whereas ongoing increased production may require investigation of an underlying condition.
How can you tell whether a high RBC count is temporary?
The appearance of a single abnormal result cannot reliably establish whether the change is temporary. A healthcare professional will consider the result alongside your medical history, medicines, recent illness, fluid intake, smoking history, altitude exposure, symptoms, and previous blood tests. The laboratory's reference range also matters because expected results can differ between laboratories and according to factors such as age and sex.
According to Cleveland Clinic, evaluating erythrocytosis begins with reviewing medical history, medicines, lifestyle, and symptoms to help identify a possible relative increase. A clinician may then decide whether repeat blood testing or additional investigations are appropriate.
What tests might be needed?
A repeat CBC may help show whether the elevated result persists. The timing should be determined by the healthcare professional based on the original findings and possible cause. The clinician may also review hemoglobin and hematocrit, which provide related information about red blood cells, rather than interpreting the RBC count alone.
If the result remains higher than expected, additional tests may be considered according to the clinical situation. These can include measuring oxygen levels, checking kidney function, or measuring erythropoietin. In selected cases, testing for changes associated with bone marrow disorders may be appropriate. Not everyone with a high RBC count needs every test.
Tell your healthcare professional about recent fluid loss, changes in where you live or travel, and all medicines or hormone treatments you use. This information can help guide decisions about repeat testing and whether further investigation is necessary.
When should you seek medical attention?
Arrange a medical review if your RBC count remains higher than expected, rises on repeated tests, or occurs alongside concerning symptoms. A clinician can assess whether the finding is related to fluid balance, oxygen levels, medication use, or another health condition.
A high laboratory result alone does not establish an emergency. However, seek emergency medical care if you develop sudden chest pain, significant difficulty breathing, coughing up blood, or signs that may indicate a blood clot or stroke. The NHS guidance on erythrocytosis highlights the importance of urgent assessment for symptoms associated with serious clot-related complications.
Do not assume that a high RBC count will resolve on its own. If dehydration or another temporary factor is suspected, follow the recommended plan for addressing it and ask whether repeat testing is needed to confirm that the result has returned to the expected range.