translation agency

Being Alive
Understanding Your Blood Work

March 5, 1994
Being Alive 1994 Mar 5: 9

Complete Blood Count (CBC) Perhaps the most routine test is the complete blood count (CBC). The CBC examines formed elements (red blood cells, white blood cells, platelets), and plasma (which is made of water, protein and other substances). HIV+ people with no symptoms should have a CBC every six to twelve months. Those with symptoms should have a CBC every three to six months but those on AZT (particularly within the first four to six months) should have it done every few weeks.

White blood cells (WBC). White blood cells or leukocytes defend the body against infection. The total number of white blood cells ranges from 4,000 to 11,000 per cubic millimeter in the average healthy adult. A high WBC count may mean the body is fighting an infection. A low WBC count may mean there is a bone marrow problem either from chronic disease or from drugs like AZT or ganciclovir. Tuberculosis, histoplasmosis, and other fungal diseases may also cause bone marrow problems such as "cytopenia" or low cell counts.

Red blood cells (RBC). These cells carry oxygen throughout the body. The number of RBCs within the normal range varies from 3.6 to 6.1 million per cubic millimeter. Too many RBCs (or platelets) in the bloodstream may cause slow blood flow and compromise circulation. A low RBC may signify anemia, a shortage of red blood cells, or hemoglobin; this usually reflects underproduction or premature destruction of the cells.

Hemoglobin is a protein that enables RBCs to carry oxygen from the lungs to the rest of the body. The amount of hemoglobin determines how much oxygen the RBCs are capable of carrying to other cells. Normal hemoglobin levels range from 12 to 16 grams per deciliter for women and 13.5 to 18 for men. These levels are often low, among HIV+ people, even those not on medications. Epogen is an injectable drug that stimulates the production of red cells. It is used in anemic AIDS patients to reduce the frequency of transfusions.

Hematocrit is the volume of RBCs expressed as a percentage of the total blood volume. If you spin a sample of blood so that the cells settle to the bottom of the tube, the percentage of volume occupied by the cells alone is called the "hematocrit." The hematocrit shows the oxygen-carrying capacity of the blood. This value also tells whether the blood is too thick or too thin. The average range is 40%-54%.

Mean corpuscular volume (MCV) is the average volume of the individual red blood cells. MCV is calculated by dividing the hematocrit by the total RBCs. The average range is 81-101 femoliters. A low MCV indicates the cells are smaller than normal. This most commonly occurs because of an iron deficiency or chronic disease. AZT may cause the MCV to rise above normal, which may also happen if there is a B12 deficiency.

Mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) are measures of the amount and volume of hemoglobin in the average cell. The MCH average range is 27-35 picograms. The MCH results from dividing total hemoglobin by total RBCs. The average range from MCHC is 31-37%.

Platelets are an element of the blood that are important for blood clotting. They are formed in the bone marrow. Too many platelets may cause "sludging" of the blood flow. People with HIV disease may have low platelets or "thrombocytopenia." Drug reactions may also be responsible for the destruction of RBCs or platelets. The average platelet count is 150-440. The chance of major bleeding rises as the platelet count drops.

Differential is a breakdown of the different types of white blood cells and is usually expressed as a percentage of the total WBCs. Multiplying these percents by the total WBCs gives the "absolute" counts. For example, if the percent of lymphocytes is 30% and the total WBCs is 10,000, the absolute lymphocyte count is 3,000.

Segs, Neutrophils, Polys (polymorphonuclear cell) are WBCs involved in fighting bacterial infections. Neutropenia is a drop in the absolute neutrophil count to below 500. Neutropenia makes people with AIDS especially susceptible to bacterial infections.

Lymphocytes (lymphs) are cells that produce antibodies, regulate the immune system, and fight viruses and tumors. The T4 or CD4 cell is part of this lymphocyte family, but is not included as part of a routine CBC. Ranges vary from 10-45%.

Monocytes or Macrophages (Monos) are WBCs involved in fighting bacterial infections.

Eosinophils (Eos) are WBCs usually involved in allergic-type reactions. An elevated eosinophil percentage can help in diagnosing certain types of allergic diseases. Ranges vary from 0-8%.

If all three major blood counts (RBC, WBC and platelets) are unexplainably low, particularly in advanced stages of HIV infection, one might consider the possibility of an opportunistic infection (especially MAC or CMV) as well as underlying HIV infection suppressing the bone marrow, or malignancies such as lymphoma.

Chemistry (Chem) Panel A large part of your laboratory report examines chemicals in your blood and identifies whether body processes are working correctly. Typically, 24 of these values are included in a "Chem 24 report," also known as a SMAC or SMA20. Your physician or clinical nurse manager may be able to help you decipher your lab values. Chemistry panels should be administered once a year if you're not taking medication, more often if you are.

Here are some of the more important values for people with HIV disease.

Glucose is sugar in the blood, most commonly used to monitor diabetes mellitus. Glucose levels may become abnormally high or low when pentamidine is given intravenously.

Sodium, Potassium, and Chloride are also known as electrolytes. These must be monitored carefully in dehydration, kidney disease, and during intravenous therapy (especially with foscarnet). Sodium levels reflect salt/water balance. Potassium levels rise in kidney failure, and may be low after severe vomiting or diarrhea.

BUN stands for blood urea nitrogen. This tends to rise in dehydration and in kidney or heart failure. Prednisone and other steroids may cause BUN to rise.

Albumin is one of the two major types of protein in the blood. Manufactured in the liver, albumin decreases in chronic liver disease. It also reflects one's general nutritional status.

Globulins are a mixture of proteins that include immunoglobulins, or antibodies. Globulins tend to rise in asymptomatic HIV+ people.

A-G Ratio is the ratio of albumin to globulin.

Bilirubin derives from the hemoglobin of dead RBCs. Bilirubin is excreted by the liver as part of the bile. Bilirubin causes the yellow color of the skin and eyes (jaundice) which occurs in hepatitis, bile duct obstruction, and other liver disorders.

Gamma GT, SGOT, SGPT, and LDH are liver enzymes. Elevation of these tests is most common in liver disease, but may also rise from injuries, tumors and drug reactions. People with Pneumocystis pneumonia tend to have a more serious prognosis if they have elevated LDH.

Iron is an essential component of hemoglobin. The iron screen is useful in identifying iron deficiency, which causes anemia (low red blood cells and hemoglobin). Iron loss may be due to chronic bleeding, for instance, when Kaposi's sarcoma affects the intestines.

Cholesterol and Triglycerides are fatty substances found in the blood. They are measured to assess risk for coronary heart disease and to follow the effect of dietary manipulations. Medication is sometimes used to lower cholesterol if diet doesn't work alone. Triglyceride levels tend to be elevated in later stages of HIV disease, and this may be due to elevated levels of TNF (tumor necrosis factor).

Markers for HIV Progression Many markers measure the presence or absence of HIV in the human blood. HIV surrogate markers are measurements that effect HIV activity; they are "surrogate" because they do not measure the absolute amount of HIV. Instead they measure secondary effects of HIV on the body. Healthcare providers often use surrogate markers to decide on drug therapies and to monitor the effects of experimental treatments. Virologic markers, such as p24 antigen, are used to directly measure the presence of HIV in the human body.

CD4 Count the most commonly used marker to determine HIV progression is also known as the CD4 lymphocyte count or T4 cell count. HIV attacks CD4 cells which help fight infections. T-lymphocytes include other CD4 (helper) cells and CD8 (suppressor) cells.

A significant drop in the CD4 count reflects the amount of damage in the immune system. CD4 levels can be reported in the following ways: - Absolute number of CD4 cells per cubic millimeter (mm3).

- Percent of CD4 cells compared to all lymphocyte cells.

- Ratio of CD4 cells to CD8 (or T8) cells.

HIV+ people should have their CD4 counts taken every three to six months, and sometimes more often if they are taking medication or if their CD4 count falls below 250. The normal range for an adult male is 800-1500 CD4 cells.

CD4 Percentage a comparison of the number of CD4 cells to the total lymphocyte count (B- and T-lymphocytes). The CD4 percentage may be a more accurate measure of HIV disease progression than the CD4 count, because immune suppression may be present despite a high CD4 count. A CD4 percentage below 20% suggests serious immune deficiency, even if the CD4 count is high.

Beta 2 Microglobulin (B2M) a protein that may become elevated in HIV+ people because of lymphocyte activity. Levels can be checked in the blood and urine. B2M may not be a good marker of HIV progression among intravenous drug users because B2M levels do not seem to correlate with disease progression among IDUs.

B2M results tend to fluctuate much less than CD4 counts. B2M levels above 5.0 milligrams per liter may indicate an increased chance of HIV disease progression.

Neopterin a protein secreted by macrophages, white blood cells that act as reservoirs for HIV. Neopterin levels rise as HIV disease progresses. Monitoring both B2M and neopterin levels may be redundant because studies show that each is about equally capable of predicting disease progression. Normally, neopterin levels are below 2.0 nanograms per milliliter. Levels above 15.0 nanograms per milliliter indicate disease progression.

p24 antigen one of the proteins that make up HIV. An antigen is anything that the immune system identifies as foreign. A positive p24 antigen test suggests active HIV replication. Someone who tests positive to a p24 antigen test, even with CD4 counts above 500, may be advised to start antiretroviral therapy. Levels are usually highest both early and late in the course of HIV disease. This test is sometimes used to monitor the progress of HIV disease and the body's response to antiviral drugs.

p24 antibody an antibody produced by the immune system in response to p24 antigen. Low levels of p24 antibodies are associated with HIV disease progression. A low p24 antibody level with high neopterin level and thrush is a sign of rapid HIV disease progression. p24 antibody levels are less standardized than the p24 antigen levels.

In the procedure known as Passive Hyperimmune Therapy (PHT), p24 antibodies from healthy asymptomatic people are infused into people with later stage HIV disease.

www.aegis.org