The Core Message
Polycythemia means there are more red blood cells than average.
Most people with a high hemoglobin or hematocrit fall into the secondary category rather than the PV (polycythemia vera) category.
The goal is to determine whether this is:
- a normal or temporary response to something (oxygen level, smoking, sleep apnea, hormones)
- a laboratory concentration issue (dehydration)
- or a true bone marrow condition (PV)
PV is uncommon, affecting about 2–3 people per 100,000, so most elevated red cell counts have other explanations.
Most causes of secondary polycythemia do not increase clot risk.
A Simple Script You Can Adapt
“We can think of polycythemia as having two main buckets of causes.
In the first bucket is one condition called polycythemia vera — or PV.
In the second bucket is everything else that can raise red blood cells.
PV is uncommon.
Most patients fall into the second bucket, where the body is responding normally to a signal such as lower oxygen, smoking, sleep apnea, high altitude, or hormones.
Sometimes we notice higher red cell counts during routine testing or after changes in health, oxygen levels, or sleep.
That means today’s finding is often the beginning of the sorting process, not evidence of an urgent problem.
In PV, the bone marrow acts on its own, making red blood cells even when the body is not asking for more.
PV is a bone marrow condition, and it not only raises red cells — it also affects platelets and inflammation. Those changes together increase the risk of blood clots.
In secondary polycythemia, red cells are responding appropriately to outside signals, and the clotting risk usually comes from the underlying condition, not the red cells themselves.
A very helpful test called JAK2 mutation testing helps us distinguish these buckets.
If JAK2 is positive, we strongly consider PV.
If JAK2 is negative, especially repeatedly, PV becomes very unlikely, and we look toward secondary causes.”
Optional Additional Reassurance
“Most people with a high hemoglobin turn out to be in the secondary bucket, not the PV bucket.
Even when PV is diagnosed, it is a chronic, slow-moving condition, and with treatment, most patients do very well.”
Helpful Analogies You Can Borrow
Tip: Choose one or two analogies that match your patient’s age, background, or communication style.
Analogy A — Two Containers
Imagine I’m holding two containers.
In my left hand is a small container with one condition — PV.
In my right hand is a large container with all the other reasons red cells go up.
PV is uncommon, and most people land in the right-hand container.
Analogy B — Thermostat and Furnace
Your bone marrow is like a furnace controlled by a thermostat.
In secondary polycythemia, the thermostat is turned up because the body wants more oxygen.
In PV, the furnace ignores the thermostat, producing heat (red cells) even when it shouldn’t.
Analogy C — Two Types of Red Cell Behavior
In secondary causes, red cells are following orders.
In PV, red cells have gone rogue, making more of themselves even without a signal.
Analogy D — Why JAK2 Matters
Think of JAK2 as the sorting key.
A positive JAK2 suggests PV.
A negative JAK2 moves us strongly toward the secondary causes container.
Analogy E — Testing Tie-In: What the CBC Really Shows
A CBC tells us the hemoglobin and hematocrit, which reflect the level of red cells in the blood.
What it doesn’t tell us is why those levels are high.
That’s why we check the JAK2 mutation and look at things like oxygen levels, sleep apnea, smoking, or hormones.
The pattern over time, together with these tests, tells us which bucket you’re in.
Common Patient Worries and How to Address Them
“Does this mean I have cancer?”
PV is classified as a type of chronic blood cancer, but it behaves very differently from fast or aggressive cancers. It usually progresses slowly, is highly treatable, and most people live normal lives for many years. Most people with a high hemoglobin do not have PV.
“Is my blood too thick?”
Rather than thinking about ‘thickness,’ it’s more accurate to say there are more red cells than usual. In secondary causes, the level is usually not dangerous by itself. In PV, the level matters because keeping the hematocrit below about 45% reduces the risk of blood clots. At very high levels, some people may develop hyperviscosity symptoms such as headaches, dizziness, visual changes, or ringing in the ears — and that is one reason we monitor and treat PV.
“Am I at higher risk for blood clots?”
Only PV clearly increases clot risk.
Most secondary causes do not increase risk from the red cells themselves.
Some secondary causes — such as smoking or sleep apnea — have their own health risks, and treating them helps overall health.
“Do I need treatment?”
PV requires reducing the hematocrit and sometimes adding medication.
Secondary causes are treated by addressing the underlying issue, not by removing blood.
“Why do I need the JAK2 test?”
Because JAK2 helps us sort between PV and secondary causes — two very different categories.
Suggested Teach-Back Questions
- What are the two main buckets of causes for polycythemia?
- Why does PV behave differently from secondary polycythemia?
- What does the JAK2 test help us decide?
- What symptoms or changes should make you contact me sooner?
Phrases to Avoid (and What to Say Instead)
- Avoid: “Your blood is dangerously thick.”
Say instead: Your red cells are higher than average, and our job is to understand why. - Avoid: “This always means something serious.”
Say instead: Most people with high red cells fall into the secondary bucket, not PV. - Avoid: “We don’t know what’s going on.”
Say instead: The JAK2 test and a few other checks will tell us which category you’re in.
Counseling Tips Based on Communication Science
- Reassure early — most cases are secondary.
- Normalize the diagnostic process — two buckets, one sorting key.
- Use the furnace/thermostat analogy to explain PV vs secondary.
- Avoid discussing clot risk until PV is confirmed.
- Anchor safety by emphasizing that trends and JAK2 results guide decisions.
- Provide a timeline for follow-up and next steps.
Optional Script for Persistent or Markedly Low Counts
Your lymphocyte count has stayed low over several tests. That doesn’t automatically mean something serious, but it does tell us it’s worth looking a little deeper.
We’ll check for things like nutritional deficiencies, autoimmune conditions, or certain infections. Most causes are treatable, and many people with low lymphocytes continue to do very well.
Micro-Script for Very Short Visits or Patient Portal Messages
Your hemoglobin is higher than average. There are two main categories of causes — PV and secondary causes. Most people fall into the secondary group.
A test called JAK2 helps us sort between the two.
We’ll repeat your blood counts and follow up once the JAK2 result is back. There is nothing today that suggests urgency.