Understanding the Complete Blood Count (CBC)

I got a blood test, a CBC.  I had never paid attention to these things before, but now I decided that perhaps I should.  Tracking down plausible explanations that I could understand took some work, so I thought I would record it for future reference by myself and others.  MedlinePlus describes itself as "a service of the U.S. National Library of Medicine and the National Institutes of Health."  I was under the general impression that these were reliable sources of information, so I decided to lean toward whatever information I could get from MedlinePlus, supplemented as needed by other sources.

An important consideration to keep in mind, for many of the measures discussed in this post, is the occurrence of change.  Doctors sometimes speak of doing the tests so as to establish a baseline, so that a later test can help to detect whether a certain value is changing in an unwelcome direction, even if it does still remain within the generally accepted boundaries.

Components of the CBC

MedlinePlus said that a Complete Blood Count (CBC) measures the numbers of red blood cells (RBCs), white blood cells (WBCs), and usually platelets (PLTs); the total amount of hemoglobin (Hb or HGB); the hematocrit (Ht or HCT) (defined as the fraction of the blood composed of red blood cells); and information about the average red blood cell size (MCV), the amount of hemoglobin per red blood cell (MCH), and the amount of hemoglobin relative to the size of the cell (hemoglobin concentration) per red blood cell (MCHC).

I didn't know much about any of those things.  I was also confused because one of the lab reports I was looking at was apparently more than a CBC.  It had things that weren't on that list (above), things like "NE%" and "MO#."  That document said it was a "CD A" sample type, but my search for something explaining a "CD A" blood sample went nowhere. MedlinePlus didn't seem to have anything on blood NE and MO. Eventually I found a Laboratory Procedure Manual that suggested that I was looking at the results of a "CBC with Five-Part Differential."  This manual was prepared by NHANES, which turned out to be short for the National Health and Nutrition Examination Survey.

I did a search for the five-part differential CBC.  Among the top hits, the Free Dictionary said that this was "A standard automated differential count of WBCs generated by an automated hematology analyzer--AHA from the peripheral circulation, which divides WBCs into neutrophils--PMNs, eosinophils, basophils, lymphocytes, monocytes."  So apparently I was looking at abbreviations for that list of neutrophils:  NE, EO, BA, LY, and MO.

This seemed to be what I needed to understand the letters on my lab report.  Now I needed to figure out how to interpret the numbers. MedlinePlus seemed to indicate that the main focus was on red (RBC) and white (WBC) blood cells and hemoglobin (HGB).  Likewise, much of the information that appeared on my CBC with Five-Part Differential seemed to focus on details about RBCs and WBCs.  I decided to start with RBCs.

CBC Interpretation, Part 1:
Red Blood Cell Measures

Various sources (e.g., MedlinePlus, MedicineNet, Laura Dean of the National Center for Biotechnology Information) listed several measurements related to RBCs.  These included the RBC count itself, as well as HGB, HCT, MCV, MCH, MCHC, and red cell distribution width (RDW).  This section discusses these measures.

Red Blood Cell Value 1:  RBCs

According to MedlinePlus and my lab report, the red blood cell count (RBC) should be between 4.70 and 6.10.  This differed somewhat from that Laboratory Procedure Manual, which I had now located in PDF form.  On pages 29-30, the manual provided these "Reference Ranges (Normal Values)" for the items I was looking at (depending on your screen's resolution, you may want to click on the chart or hit Ctrl-+ to make it larger):



So as a fiftyish male, this chart said my RBC should be between 4.10 and 5.80 million (i.e., 10^6) cells per microliter (i.e., uL or μL) of blood.  The lab report I was looking at did not state my race, weight, or other information that might have explained why their values differed from those of the chart.  MedlinePlus did say that most of these counts would vary with altitude.  As another point of comparison, WebMD agreed on a range of 4.70 to 6.10, with somewhat lower values for women and children (but still not as low as those shown in the chart, above). MedicineNet didn't distinguish by age or gender; they just said the normal range was about 4.2 to 5.9.  Wikipedia provided a chart showing that different sources set the upper limit for adult males, for instance, to anywhere between 5.7 and 6.9.  These variations seemed odd, given Wikipedia's statement, elsewhere, that normal ranges in blood data tended to mean the range in which 95% of the normal population fell. LabTestsOnline said that a reading slightly outside the reference range might not matter; they said that a doctor might respond to that sort of thing by re-running the CBC.

MedlinePlus named a variety of reasons why a person might have an abnormally high or low RBC count.  Examples on the high side included smoking, congenital heart disease, and kidney tumor.  Examples on the low side included leukemia, malnutrition, and overhydration.  A New York Times article provided a longer list.  For all of these tests, certain medications could also affect the counts. LabTestsOnline said, "Fatigue may indicate a low or high RBC count. Fainting, pallor, shortness of breath, dizziness, and/or altered mental status can also indicate low RBCs. Disturbed vision, headache, and flushing may be present with increased numbers of RBCs."

Several searches failed to give me a clear picture of what would count as an extreme or danger-level RBC -- as distinct from, say, one that was abnormal but not really frightening.  Of these various searches, the most promising appeared to be the one in which I named specific problems (e.g., smoking); but it still wasn't getting me anywhere fast. At a certain point, I noticed that the Laboratory Procedure Manual (above) named "panic values" for several other measures (see below) but not for RBCs.  It seemed, then, that RBC values themselves were a sort of art, with doctors varying in their appreciation for or alarm at a given value.  After quite a bit of effort to learn more than that, I decided to move on and see what insight might emerge from other, apparently more precise measures related to RBCs.

Red Blood Cell Value 2:  HGB
(with a comment on the quality of information provided online)

Going down the list in the chart (above), hemoglobin (HGB) for a fiftyish male was apparently supposed to be in the range of 12.7 - 17.1 grams per deciliter (i.e., tenth of a liter) (g/dl).  My lab report said 14.0 - 18.0, however;  MedlinePlus said 13.8 - 17.2 for males generally; MedicineNet said 13.0 - 18.0; and Wikipedia, apparently not yet updated for the several sources just cited, said that sources ranged from a low of 13.0 to a high of 17.5. The National Anemia Action Council stated that the U.S. Food and Drug Administration prohibited blood donations by men with hemoglobin below 13.0.  The Laboratory Manual (above) named "panic values" of 6.5 on the low end and 18.0 on the high end. Ron Kennedy suggested that hemoglobin values under 5 "gm" [sic] may cause heart failure, and values over 20 gm may cause clogging of capillaries.  Mayo Clinic research has linked low hemoglobin with Parkinson's Disease 20 to 30 years later.

When I sought information about symptoms of low or high hemoglobin, I noticed (as I had noticed in other searches) that the top  Google results tended to come from sites with names like eHow.com and Buzzle.com, and that frequently the answers were as much opinion as knowledge -- or, in a glorified version of this phenomenon, from places like Wellsphere, owned by HealthCentral, whose management team appeared to include no doctors and almost nobody with doctoral degrees of any kind.  Wellsphere's own management team included just one doctor; likewise its board of advisors.  A search for symptoms of low or high hemoglobin brought me very few hits from non-commercial websites.  One problem with a commercial orientation in health information was, of course, the potential for conflicts of interest, such as those involving funding or advertising that involves pharmaceutical companies and health care equipment providers.

There seemed to be, in other words, a gap between the information needs of the public and the orientation of the medical profession -- a void that seems to invite individuals from other backgrounds. As a relatively benign example,  Sandy Rothra at eHow.com pointed toward an American Red Cross page that described anemia as the medical term for low hemoglobin.  But things did not appear to be that simple. According to the Iron Disorders Institute, it was possible to have too little iron (equated with low hemoglobin on that Red Cross page) and yet have too much iron at the same time.  WrongDiagnosis.com said there were many types of anemia; and as with RBCs (above), MedlinePlus indicated that low HGB can be due to a variety of sources, including not only anemia but also bleeding, leukemia, malnutrition, and overhydration, and that high HGB could be due to congenital heart disease, dehydration, and low blood oxygen.  Those conditions could have varying creauses and symptoms. Equating anemia with low hemoglobin, Ms. Rothra claimed that "Patients most often complain of fatigue and weakness with a low hemoglobin count, according to the National Heart, Lung and Blood Institute."  But the NHLBI page that Ms. Rothra cited was referring specifically to iron-deficiency anemia, not to low hemoglobin generally.  Equating them could be dangerously misleading.  A person is not going to fix leukemia by taking One-a-Day Multiple Vitamins with Iron.  Elsewhere, the NHLBI did make clear that anemia and low hemoglobin are not synonyms.

According to California Pacific Medical Center, symptoms of low hemoglobin include shortness of breath while doing simple tasks, fatigue, paleness, chilliness, dizziness, irritability, headache (to which Stephan added ringing in the ears).  That did substantially match up with the NHLBI's list of symptoms of iron-deficiency anemia, although the latter also included chest pain (and, in children, poor appetite, slowed growth and development, and behavioral problems).  About-Blood-Disorders.com stated that anemia could also produce rapid heartbeat and weakness. The Iron Disorders Institute added depression, sore tongue, restless legs syndrome, and loss of interest in work, recreation, relationships, and intimacy.  It appeared that the intensity or reliability of such symptoms could vary greatly according to the degree of low hemoglobin; one study of pregnant women in Liberia found significantly lower HGB levels in those who complained of headaches.  Causes of iron deficiency (which, again, is not strictly identical to low hemoglobin) could include age; gender; ethnicity; consuming foods or substances that impair iron absorption (e.g., coffee, milk, calcium supplements, eggs, chocolate, aspirin, antacids); being a super blood donor; certain diseases and disorders (e.g., sickle cell anemia, diseases of the digestive tract or endocrine system, gastric banding, bulimia); inadequate iron intake (e.g., strict vegetarianism); excessive aerobic exercise; certain chemicals (e.g., lead); drug abuse (including pain medications and alcohol); surgery; and infection.

On the high side, symptoms of "iron overload" could include chronic fatigue, joint pain, abdominal pain, liver disease (cirrhosis, liver cancer), diabetes mellitus, irregular heart rhythm, heart attack or heart failure, skin color changes (bronze, ashen-gray green), loss of period, loss of interest in sex, osteoarthritis, osteoporosis, hair loss, enlarged liver or spleen, impotence, infertility, hypogonadism, hypothyroidism, hypopituitarism, depression, adrenal function problems, early onset neurodegenerative disease, and elevated blood sugar.  Note that both over- and under-supply of iron could thus produce some of the same symptoms. Causes of iron overload could include excessive iron shots, supplements, or blood transfusions; excessive amounts of foods that contain or enhance iron absorption (e.g., red meat, supplemental vitamin C, alcohol, sugar); regular tobacco smoke or use; risk factors for metabolic syndrome that heighten the risk of type 2 diabetes and cardiovascular diseases; inherited iron-loading conditions (e.g., hemochromatosis); exposure to iron-containing asbestos; and working and/or living in subways, iron smelters, coal mines, and highly polluted areas.

Red Blood Cell Value 3:  HCT

Hematocrit (HCT) was next on the list in the chart (above). For a man (especially, I now assumed, a white man) in his 50s, the chart said I should be in the range of 38.0% to 50.3%.  As noted above, this was the percentage of the blood composed of red blood cells.  Wikipedia said that various sources had put the range from as low as 39% to as high as 62%, but on a different page stated that it was normally about 48% in men.  MedlinePlus said 40.7% to 50.3%. In terms of danger zones,  Bloodbook indicated, without citation, that the body can typically compensate for a loss of as much as 70% of its red blood cell mass, which would mean an adult male hematocrit as low as 14% (i.e., 30% of 48%), though of course it might be advisable to ask what in the world was causing that level. Random sources suggested that a hematocrit might be considered very low below 30% or below 24%, and that a hematocrit around 34% would be moderately low.  That said, people with hematocrits below 38% were reportedly prohibited from donating blood, even though 36% would still be considered healthy for women (with other levels for children and pregnant women).

According to MedlinePlus, a low hematocrit could result from certain diseases (e.g., lupus erythematosus, rheumatoid arthritis, kidney disease, leukemia, multiple myeloma), blood loss, bone marrow failure, or malnutrition. Wikipedia cited additional conditions specific to women and children. Symptoms of low hematocrit did not appear to be markedly different from those of other red blood cell deficiencies summarized above, although again I was struggling to find credible sources of relevant information.  For instance, the top items on my Google search came from HomeRemediesForYou.com and the aforementioned Wellsphere.

On the high side, one book (p. 385) indicated that 60% would be quite high; another random source considered 60% "extreme." A Merck webpage stated that a high hematocrit was considered an indicator of a disease called polycythemia vera:  "Without treatment, about half of the people who have polycythemia vera with symptoms die in less than 2 years. With treatment, they live an average of 15 to 20 years."  Tamer Fouad said, "A hematocrit greater than 60% is always associated with an increase of RBC mass and is diagnostic of polycythemia. For hematocrit values of 50% to 60%, the diagnosis of polycythemia requires direct measurement of the RBC mass."  According to MedicineNet, though, polycythemia vera is extremely rare in the U.S., occurring in about one person per million; but there are other kinds of polycythemia.  In the familiar list, but with some variations, they said that symptoms of high hematocrit included weakness, fatigue, headache, itching, bruising, joint pain, dizziness, or abdominal pain, and that risk factors included smoking, chronic lung disease, chronic carbon monoxide exposure, living at high altitudes, and certain genetic mutations.  MedlinePlus said that a high hematocrit could also result from dehydration, kidney disease, congenital heart disease, and other disorders (especially cor pulmonale and pulmonary fibrosis).

Red Blood Cell Values 4, 5, 6, and 7:  MCV, MCH, MCHC, and RDW

MedlinePlus combined its treatment of average red blood cell size (MCV), hemoglobin amount per red blood cell (MCH), and the amount of hemoglobin relative to the size of the red blood cell (MCHC). These three, it said, were RBC indices, and their purpose was to diagnose the type of anemia.  In my understanding of the Encyclopedia of Surgery, these three, as well as the red cell distribution width (RDW), could be calculated on the basis of other values described above, without requiring additional measurements.  As calculated values, it did not appear that these figures would be presented in any terms other than those that were standard for the measures (e.g., femtoliters), so I did not dwell upon their terms of expression. That is, I just focused on the values, without paying much attention to what they represented or how they were calculated. For that purpose, MedlinePlus and MedicineNet stated normal values for MCV (80-100), MCH (27-31 or 27-32), MCHC (32-36), and RDW (11-15).

I was not anemic, so I was not really concerned about these indices.  I was curious, though, about the fact that my lab report nonetheless stated low and high values for them.  Would there be any significance to a low or high value for one of these submeasures even without anemia -- or were they meaningful only for people with anemia?  My question, and my search, revealed what I was recognizing, by now, as the usual public uncertainty about what the measures meant in various circumstances.  (As the reader may have surmised, my lab report did not even come with an explanatory brochure, much less a comprehensive interpretive guide.)

For this one, I went into the medical literature, rather than relying on popular reports.  I encountered the interesting case reported by Rao et al., in which a 23-year-old lifelong vegetarian met DSM-IV criteria for major depressive disorder with psychotic symptoms.  Rao et al. refer to research indicating that Vitamin B12 (cobalamin) deficiency could result in psychiatric symptoms that precede hematological symptoms by as long as eight years.  In other words, mental condition can warn of dietary shortcomings long before they are manifested in the blood.  Symptoms of B12 deficiency could include depression, apathy, irritability, dementia, catatonia, delirium, and hallucinations.  The client had low hemoglobin (11.9), high MCH (43.9), high MCHC (36.2), high MCV (121.1), and low B12. According to MedlinePlus, the high MCV would meet the definition of macrocytic anemia, and the high MCH would meet the definition of hyperchromic anemia -- which could be described, together, as macrocytic hyperchromic anemia. I found this case useful for helping me to gain a degree of orientation to the discussion, and also for its discussion of relevant research, as just summarized. That case did feature anemia.

In another case, however, Maamar et al. identified a 33-year-old woman whose RBC tests were all normal, but who was experiencing a neuropsychiatric disorder without anemia -- resolved, again, with B12 injections.  Maamar et al. cited some apparently classic work by Lindenbaum et al. in which, they said, patients in a number of cases had abnormal HGB and/or MCV without anemia.  In a very different direction, Cavusoglu et al. found that high RDW was "a strong and independent predictor of all-cause mortality . . . [among men] referred for coronary angiography."  So I concluded that abnormal values in at least some of these RBC indices -- MCV, MCH, MCHC, and/or RDW -- could signal issues even without anemic values of RBC, HGB, or HCT.  I didn't investigate all of the possible things that various combinations of high and low values of these RBC indices might indicate.

CBC Interpretation, Part 2:
White Blood Cell Measures

As with RBCs, there seemed to be several different WBC measurements in the CBC with Five-Part Differential.  Or as About.com corrected me, there were five different types of WBCs: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. According to MedlinePlus, these were counted via the Blood Differential test.  This terminology led me to think that apparently a regular CBC, without the Five-Part Differential, would include the foregoing RBC measures but would not include anything for WBCs other than the overall WBC count. I verified this by checking a MedlinePlus webpage on the CBC, and also by taking a look at a report of an older blood test in my file from another medical center (described, in that case, as a hemogram).  It had all of the other values discussed above, but not these five components of the Blood Differential test.

White Blood Cell Value 1:  WBCs

The purpose of RBCs is to carry oxygen; the purpose of WBCs is to fight infection.  According to MariAnne, a senior nurse in Adelaide, the ratio of RBCs to WBCs is about 700:1.  MedlinePlus said that a normal WBC count would be in the range of 4,500 to 10,000 white blood cells per microliter (mcL).  My lab report put the range somewhat higher, at 4.8 to 10.8 (thousand).  For my age group, the chart (above) stated a broader range of 3.9 - 12.1. Wikipedia said that various sources set the lower end at several different values between 3.5 and 4.5, and the upper end between 9.0 and 11.0.

According to MedlinePlus and Laura Dean, a high number of WBCs (called leukocytosis) typically indicates an immune system response (e.g., the body is fighting an infection), but may also indicate a WBC tumor (e.g., leukemia) or the effects of a variety of drugs (e.g., NSAIDs).  The Gale Encyclopedia of Medicine said that leukocytosis could also occur naturally after a large meal or after experiencing stress, intense excitement, or vigorous exercise.  Michael Gibson stated that leukocytosis was very common in very ill patients, and (in addition to the causes just mentioned) could result from hemorrhages, steroids, burns, comas, Down Syndrome, and seizures.  As with RBCs, the Laboratory Procedure Manual (above) stated a "panic level" for WBCs at or above 16.0.  According to Gibson, a leukemoid reaction was said to occur when the WBC count exceeded 25 or 30.  Various sources seemed to say that extreme leukocytosis could involve WBC counts of 40, 50, or even 100.  Yitta et al. defined "hyperleukocytosis" as a WBC count of over 100, and seemed to say that this level (typically occurring in leukemia and some other disorders) presages death within a few weeks.

Gibson indicated that leukocytosis and leukopenia were not disorders, but were simply lab results.  This seemed to mean that they did not have observable symptoms of their own, but were rather just consequences of other disorders. MedlinePlus and Laura Dean said that a low number of WBCs (leukopenia) occurs when the bone marrow fails to produce WBCs (usually because of toxins or tumors in the bone marrow) or, more commonly, when a diseased liver or an overactive spleen is removing too many WBCs from the blood.  Dietary deficiencies and some drugs (e.g., antibiotics, diuretics) could also lower the total WBC count. Michael Gibson named a number of diseases (e.g., HIV, flu, malaria) and other conditions (e.g., alcoholism, B12 deficiency) that could produce leukopenia, and said that a reduction in WBC count could place patients at increased risk of infection.  The Laboratory Procedure Manual stated a "panic level" here, too, for WBCs at or below 3.0.  Harrison et al. seemed to indicate that 2.5 would constitute extreme leukopenia and would tend to accompany a severe viral disease or hemorrhagic fever.

White Blood Cell Value 2:  NE

Although there were apparently many kinds of WBCs, MedlinePlus said that neutrophils (NE) tended to account for 40% - 60% of the total WBC count.  Rebecca Frey of the Gale Encyclopedia of Medicine said that, for an average adult, the normal level was 1,500 cells per cubic millimeter (mm3) of blood.  My lab report stated a range of 43% - 65%, or 2.2 to 4.8 x 10^3/μL.  For my gender and age group, the chart (above) said 39.7% - 77.3%.

According to Nancy Nordenson of the Gale Encyclopedia of Medicine, neutrophils fight infection by eating bacteria.  Wikipedia said that "neutrophil" was shorthand for the technical name of neutrophil granulocyte; that neutrophils accounted for about 70% of all WBCs; and that the normal count was 2.5 to 7.5 billion cells per liter of blood (i.e., 2.5 - 7.5 x 10^9/L).  On the separate chart cited several times (above), Wikipedia reported that neutrophils were also known as grans, polys, segs, or PMNs; that on the low side, according to several sources, they accounted for 45-54% of all WBCs (for a count of 1.3 to 2.0 x 10^9/L); and that, on the high side, they accounted for up to 62-74% of all WBCs (i.e., 5.4-7.0%).

Being below that low threshold was called neutropenia, according to Rebecca Frey, and would entail increased risk of infection. Neutropenia was caused by the various problems described for WBCs generally, including decreased WBC production, destruction of WBCs, and removal of WBCs from the blood circulation.  For women,  Stephan said, mild neutropenia would have an absolute neutrophil count (ANC) of 1.0 - 1.5, moderate neutropenia would be in the range of 0.5 - 1.0, and severe neutropenia would be below 0.5.  (ANC included not only neutrophils per se but also "bands," which were apparently neutrophils in development.) According to Bangert et al., being above the high limit just described was called neutrophilia.  Neutrophilia had many causes, mostly mentioned above (e.g., rhematoid arthritis, steroids, exercise), as well as several not listed above (e.g., labor, surgery, panic, rage).

White Blood Cell Value 3:  LY

MedlinePlus said that the second most common kind of white blood cells were the lymphocytes (LY), accounting for 20% to 40% of total WBC count. My lab report put the range at 20.5% - 45.5% (1.3 - 2.9). The chart (above) said 17.8% - 51.8% for a fiftyish male.  Wikipedia said that various sources put the low end of the normal range between 16% and 25% (0.7 - 1.0), and the high end between 33% and 45% (3.5 - 4.8). MedicineNet said there were two kinds of lymphocytes:  B cells (to make antibodies that attack foreign substances) and T cells (to attack virus- or cancer-controlled cells of the human body itself).

As with the neutrophils (above), there was the possibility of lymphocytopenia and lymphocytosis, as described on e.g., specialized Wikipedia and WikiDoc webpages. These conditions would be attributable to causes like those listed by MedlinePlus. I didn't explore those pages at this point because I felt I had the basic ideas pretty much in place by this point, for my purposes, for these aspects of the CBC Differential Test.  It also seemed that we were getting into more minor aspects of blood chemistry (though obviously of life-and-death importance to those who were affected by relevant disorders or conditions); that is, I felt I could come back to this in more detail as needed, and I wanted to get on to platelets (below) and wrap this up.

White Blood Cell Values 4, 5, and 6: MO, EO, and BA

Monocytes (MO) accounted for only 2% to 8% of WBCs, according to  MedicineNet; 4.8% to 10.8%, according to my lab report; and 0% - 12%, according to the chart (above).  Further information was available on Wikipedia and WikiDoc.  Eosinophils (EO) accounted for 1% to 4% of WBCs, according to  MedicineNet; 0.9% to 2.9%, according to my lab report; and 0% to 8%, according to the chart (above).  Further information was available on Wikipedia and WikiDoc.  Basophils (BA) accounted for 0.5% to 1% of WBCs, according to  MedicineNet; 0.2% to 1.0%, according to my lab report; and 0% to 2%, according to the chart (above).  Further information was available on Wikipedia and WikiDoc. According to MedicineNet, neutrophils, eosinophils, and basophils were all types of granulocytes.

CBC Interpretation, Part 3:

Platelet Measures

As with many of the foregoing topics, MedlinePlus had a number of webpages that discussed various aspects of platelets. Platelets, they said, were a certain type of cell. This agreed with WebMD and contradicted MedicineNet and Ron Kennedy, who said that platelets were only fragments of cells. Probably there was a technical clarification by which both could be right; nonetheless, it seemed odd that something so basic to blood chemistry would not have been reduced to common, agreed-upon terms by this point.  In any case, platelets were important for purposes of helping blood to clot, so that bleeding would not continue uncontrolled.

Platelet Value 1:  PLT

MedlinePlus and MedicineNet did agree that a normal platelet count (PLT) would be in the range of 150 to 400 x 10^3 μL.  My lab report said 130-400.  The chart (above) said 157-414.  The "panic level" stated in the Laboratory Procedure Manual (above) was 50.  At that level, Ron Kennedy said that the risk was thrombocytopenia, in which the person would bleed uncontrollably from even a minor trauma.  Signs of bleeding due to low platelet count, he said, could include easy bruising, unusual nosebleeds, black, tarry stools, and heavy vaginal bleeding.  Moreover, he said, at 20, the problem is magnified into a risk of spontaneous bleeding, without any provocation, with a serious risk of death.  Such conditions can be the result of either a failure to produce new platelets or the rapid destruction of existing platelets.  The former can occur when, for instance, the bone marrow is so busy producing WBCs in response to leukemia that it neglects to produce new platelets.  Other possible causes identified by MedlinePlus include massive blood transfusion, prosthetic heart valve, and chemotherapy.

The Laboratory Procedure Manual (above) also stated a "panic level" at 800 on the high side.  This was known as thrombocytosis, and it involved production of too many platelets. Wikipedia suggested investigation of the causes if the level reaches 750. In thrombocytosis, MedlinePlus said, possible causes included anemia, certain cancers, and recent spleen removal.  According to the Mayo Clinic, thrombocytosis does not tend to have symptoms observable outside of the laboratory, and platelet level will ordinarily return to normal when the condition causing it is resolved.  Wikipedia noted, however, that some causes (e.g., hemorrhage, iron deficiency, inflammatory bowel disease, meningitis) might require additional attention to insure that the thrombocytosis eases.

Platelet Value 2:  MPV

According to LabTestsOnline, mean platelet volume (MPV) measures the average size of platelets. This was useful information because newly created platelets apparently tended to be larger; so if the average size was large or increasing, you would know that the bone marrow was producing new platelets.  Bessman et al. were able to link high or low MPV with particular kinds of disorders, including polycythemia vera (above).  Wikipedia noted that, in some cases of increased destruction of platelets, the body may produce so-called "giant" platelets.

Conclusion

Hematology is, of course, a large and complicated field.  The purpose of this post was to take a preliminary step into it, for purposes of interpreting a CBC blood test.  The philosophy or theory guiding this effort was that, once you make that first step, you begin to have a point of reference, some way to orient yourself as you continue to encounter other information about that subject.  It did not appear, from my blood test, that I had anything in particular to worry about; but life is long, and it did not seem wise to leave all of these things in the hands of doctors, who hopefully would but might not notice some particular condition or development in my present or future bloodwork.