What should you know about a high HCT blood test?

A high HCT blood test means red blood cells make up a larger share of your blood than the laboratory reference range. HCT, or haematocrit, is read alongside haemoglobin, red-cell size, symptoms, and your medical history. One result does not identify a cause by itself.

Blood can look more concentrated after fluid loss from vomiting, diarrhoea, fever, heavy sweating, or not drinking enough. Living at altitude, smoking, or reduced oxygen reaching the body can also be relevant. Less commonly, the bone marrow may be making too many red blood cells. The result may also need checking against the sample quality and your usual readings.

Arrange a routine review so a clinician can assess the full blood count, hydration, medicines, smoking, sleep and breathing symptoms, and any recent illness. Do not start aspirin, donate blood, or change prescribed treatment just because HCT is high. A repeat blood test may be suggested when dehydration or a temporary illness could have affected the result.

Seek urgent medical help for sudden chest pain, severe breathlessness, fainting, new weakness on one side, confusion, or a painful swollen leg. These symptoms can have serious causes and should not be explained away by a blood-test result. Contact a clinician promptly if you have a persistent severe headache or visual change.

Ask which HCT value and reference range were used, whether haemoglobin and red-cell count support the finding, whether you might be dehydrated, and whether another test is needed. Mention smoking, snoring, travel to high altitude, recent illness, and every medicine or supplement you take.