Dear Doctor: I've been diagnosed with polycythemia vera, which I understand is very rare. I'm currently being treated with phlebotomies. Please explain this diagnosis and what science has learned about it.

Dear Reader: To understand polycythemia vera (PV), you must first understand how bone marrow works. For starters, the marrow is full of stem cells that eventually become red blood cells (which carry oxygen), platelets (which help the blood to clot) and white blood cells (which fight infection). Initially, however, the stem cells become either lymphoid cells (which develop into lymphocytes, a specific type of white blood cell) or myeloid cells (which develop into red blood cells, platelets or white blood cells that are not lymphocytes). PV occurs when the myeloid cells reproduce preferentially, producing more of their type of cells.

This causes a significant elevation in the number of red blood cells and, to a lesser degree, platelets and white blood cells. The origin of this proliferation is linked to a mutation in the JAK2 gene, which is only occasionally linked to a genetic susceptibility within families. More often than not, it's a random mutation.

The greatest complications of PV are due to the increased concentration of red blood cells and platelets within the blood stream. This increases the risk of blood clots, which can lead to strokes, heart attacks and a sudden loss of blood flow to other organs or to the extremities. About 16 percent of people with PV develop an arterial thrombosis, or blood clot in an artery. About 7 percent develop blood clots in the veins, which can lead to clots in the legs or lungs or in the vein to the liver and spleen.

Speaking of the spleen, 36 percent of people with PV develop an enlarged spleen. Because this organ stores red blood cells and filters out old ones, the high concentration of red blood cells mean that these cells become sequestered in the spleen, causing it to enlarge and compress surrounding structures.

One of the more irritating symptoms of PV is itching, which worsens with exposure to warm water. A more troublesome symptom is a burning sensation in the hands or feet due to alterations of blood flow in the small blood vessels in the feet or hands. This condition, called erythromelalgia, affects 29 percent of patients.

Once a practitioner is clued into the possibility of PV, he or she may order a bone marrow biopsy as well as further blood work, including checking for the mutation in the JAK2 gene.

Phlebotomy is often necessary to lower the red blood cell count, which significantly decreases the risk of blood clots. Low-dose aspirin (81 milligrams) can provide benefit too, not only by reducing the chance of clotting, but by reducing the itching of PV. And, for people over 60, or those with a history of clots, the medication hydroxyurea can help by lowering the red and white blood cell and platelet counts.

As you mention, PV is rare, occurring in 1 out of every 50,000 people per year on average. Although the condition can be life-threatening -- for all the reasons explained above -- the phlebotomies (inconvenient though they are) can help keep the disease under control.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My blood test results always include levels of HDL and LDL cholesterol, but what about lipoprotein(a)? Don't high levels triple the risk of a heart attack or stroke at an early age? If so, shouldn't doctors test for it?

Dear Reader: The short answer is: for some people, yes.

The longer answer starts with some background: Lipoprotein(a) is a type of blood protein similar to the low-density lipoprotein (LDL) commonly measured in a cholesterol test. Because its structure resembles that of the proteins plasminogen and tissue plasminogen activator (TPA), which are involved in the breakdown of blood clots, lipoprotein(a) competes with those proteins and decreases their ability to break down clots. In other words, lipoprotein(a) boosts the blood's clotting ability. This could potentially aid wound healing and repair of tissues, but no specific need for lipoprotein(a) has been found.

The big concern with lipoprotein(a) is its potential to encourage clot formation within the arteries, raising the risk of heart attacks and strokes. A 2009 study in the Journal of the American Medical Association reviewed the results of 36 studies assessing the role of lipoprotein(a) and vascular disease in a total of 126,634 people. The authors found that, with every 3.5-fold increase in the level of lipoprotein(a), there was a 13 percent relative increase in coronary heart events and a 10 percent increase in stroke rate. The authors concluded that the high lipoprotein(a) levels were an independent risk factor for heart attacks and strokes, but not as strong a risk factor as other cholesterol markers.

However, very high levels of lipoprotein(a) are a significant risk factor for coronary heart disease, as illustrated in an Italian population study. The 2014 study measured lipoprotein(a) in 826 people and then followed them for 15 years. Those with lipoprotein(a) levels greater than 45 mg/dl -- totaling 20 percent of the study group -- had 2.3 times greater odds of stroke or coronary heart disease compared to those with lower levels.

As for why some people have higher lipoprotein(a) levels than others, the answer is in our genes. Variations of lipoprotein(a) levels appear to be related to a part of a gene called apo(a). Two different variations in this gene can cause elevation of lipoprotein(a). A grouped analysis found that people with one of the variations had 50 percent greater odds of coronary heart disease, while those who had both variations had 2.5 times greater odds.

So, to answer your question: If you have a family history of early heart disease, your doctor should consider checking your lipoprotein(a) level, especially if you have no other risk factors. People who have had a heart attack without any other risk factors also should have their levels checked.

As for lowering the lipoprotein(a) level, niacin can do this at high doses (2 to 4 grams per day), as can cholesterol-lowering PCSK9 inhibitors. Note, however, that no studies thus far have assessed the benefits of doing so.

Instead, people with very high levels of lipoprotein(a) may find greater benefit in significantly lowering their overall cholesterol with statins. Statins won't lower the lipoprotein(a) level itself, but they provide greater health-related bang for the buck. Lastly, because elevated lipoprotein(a) levels increase the risk of clot formation in the arteries, people at high risk may also find it prudent to take aspirin as a blood thinner.

In summary, for most people, overall cardiovascular health should be the focus in reducing the risk of heart attack and stroke, not lipoprotein(a).

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My daughter has been talking about the merits of "raw water" -- and the perils of regular tap water. Could it be that people are really drinking non-sterilized or treated water? Isn't that dangerous?

Dear Reader: Thanks to a recent feature story in The New York Times about several companies in the United States that are selling so-called raw water, there's now a national conversation about this trend. The water referred to in the story is untreated, unfiltered and unsterilized. The purveyors claim it is bottled in the exact state that it emerges from certain springs, and attach all sorts of health claims to their products.

While these companies say that the water they sell is safe for consumption (it turns out that one of these vendors, who charges upward of $20 per gallon, is actually drawing from the very same aquifer that furnishes part of Oregon with tap water at a fraction of the cost), the idea that people would seek out so-called natural water is alarming.

The truth is that securing clean drinking water has been one of the great challenges throughout history. Untreated water can contain everything from parasites, viruses and bacteria to naturally occurring chemicals like arsenic. And while municipal drinking water certainly has its own share of black eyes, as the scandal in Flint, Michigan, has most recently illustrated, the idea that spring water is automatically safe to drink is naive and dangerous.

According to the Environmental Protection Agency and the Centers for Disease Control and Prevention, drinking untreated water puts you at risk for any number of pathogens such as E. coli, hepatitis A, Shigella, giardia and norovirus, to name just a few. Diarrhea, cholera, dysentery, typhoid and polio are all water-borne illnesses. Add in wild card pollutants like pesticides, farm waste runoff, carcinogenic compounds and leakage or even spillage from septic tanks -- all of which can leach into the ground miles upstream of a seemingly pristine spring -- and drinking "raw" water can become a genuine health risk.

Clean water is an international health issue. In developing nations, water contaminated with pathogens and pollutants accounts for 80 percent of all disease. According to the World Health Organization, more than 300,000 children under the age of 5 die each year from gastrointestinal illness associated with the lack of potable water. As any experienced backpacker will attest, drinking unfiltered, untreated or unsterilized water is a foolhardy gamble that can result in grave health consequences.

This isn't to say that public water supplies are perfect. According to a report issued by scientists with the National Resources Defense Council last year, the aging municipal infrastructure in the U.S. is taking a toll on water safety. Violations of the landmark Safe Drinking Water Act of 1974 range from inadequate testing and reporting to the presence of a host of contaminants in community water systems.

Still, in our opinion the so-called raw water movement is misguided. While some natural sources may indeed be perfectly safe, the health risks of drinking untested water from a spring or pond far outweigh the chances you take at your kitchen faucet.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)