Step Perspective, Volume 5, Number 1; A Publication Of The Seattle Treatment Education Project - February 1993
Joel Gibson, MS

There are some basic rules which hold true for nearly all laboratory tests:

1. Different laboratories can get different results on the same sample of blood. Make sure you ask your primary health care provide which lab was used if it is not noted on the report.

2. Laboratories can make mistakes. if your results have changed dramatically form your previous test, have it run again.

3. Most lab values need to be interpreted along with other clinical and laboratory data in order to develop a meaningful diagnosis. Very seldom will only one value give all of the answers.

4. Laboratory values differ according to age, sex, current medications, etc. Therefore, the interpretation of these values needs to be done with these other parameters in mind.

5. The "normal" range is the value that is normal for a person who does not have HIV. For example, a low cholesterol value in an HIV infected individual in not uncommon

CBC - The Complete Blood Count (CBC) is one of the most common tests ordered by a provider. It is a routine test used to evaluate the blood and general health. Asymptomatic, HIV positive individuals should have this test done twice a year. Symptomatic individuals should have their CBC done at least every three months. Additionally, if you are on antivirals or other medications you might need to have this test done more often. A CBC measures all the following parameters: red blood cell count (RBC), white blood cell count (WBC), hemoglobin, hematocrit, three red cell indices, and the white cell differential. Platelet counts are sometimes included in a CBC.

RBC Count - The RBC count is the number of RBCs in a cubic millimeter of blood. The RBCs are the cells produced in the bone marrow that carry oxygen to your tissues. The normal range is 4.5- 5.9 million/mm3 for men and 4.0-5.3 million/mm3 for women. a slight decreased value is not cause for alarm as many individuals with HIV infection have values below the normal range. However, a markedly decreased value should be thoroughly investigated. A person with a significantly low RBC count can have symptoms of fatigue, shortness of breath, and appear pale in color. A low RBC count can be due to progressive HIV illness or to certain medications or both. AZT, for example, can suppress the production of RBCs in some individuals. A decrease in the RBC count usually causes a decrease in the hemoglobin and hematocrit values.

WBC Count - The WBC count is the number of WBCs in a cubic millimeter of blood. The primary function of these cells is to prevent and fight infections. There are many different types of white blood cells that play specific roles in fight infections. These specific types of WBCs can be measured in the white cell differential. Normal WBC count is from 4,500 to 1,000. The WBC count can be decreased for a variety of reasons: certain medications decease the production of WBCs in the bone marrow, minor viral infections which you may not even be aware of, stress, and opportunistic infections. Values markedly decreased should be cause for concern, since during this situation one is more susceptible to other infections.

Hemoglobin - Oxygen is carried to the tissues via hemoglobin in the RBC. A normal hemoglobin level is 14.0-18.0 g/dl for men and 12.0-16.0 g/dl for women. A slow, progressive decline in hemoglobin is often seen in people with AIDS. This is usually due to a decline in the number of RBCs produced in the bone marrow. Any drug which causes a suppression of the bone marrow, will decrease the hemoglobin level. In most cases it's a matter of balancing the effects of the drug with its potential side effects. When the side effects become too great, either the drug must be removed or the dose reduced to a tolerable level. A drug which mimics the action of the hormone erythropoietin (AKA Procrit, EPO and other names), has its effect on the bone marrow causing the production of new RBCs. It has provided great relief to thousands of individuals with HIV infection and kidney dialysis patients. Erythropoietin has enabled many people to stay on bone marrow suppressive drugs without the need for transfusions.

Hematocrit - The hematocrit is the percent of the cellular components in your blood to the fluid or blood plasma. This test is one of the truest markers of anemia. Normal values for men are 40- 54% and for women 37-47%. A decrease in hematocrit is always seen with a decrease in the hemoglobin. These two values are linked to one another.

MCV - The mean cell volume or MCV is the most important of the RBC indices. It is a measure of the average size of the RBC. For those individuals taking AZT, the MCV will always be normally elevated, i.e. greater than 100. Vitamin B12 and Folic Acid deficiencies also cause increases in MCV. Normal MCV levels are 80-96.

The other 2 indices are not so important. They are the MCH and the MCHC and are used to help diagnose various anemias and leukemias.

Platelets - Platelets are cellular fragments which are necessary for the blood to clot. When activated by "trauma," platelets migrate to the site of injury where they become "sticky," adhering to the injured site and subsequently used in the developing fibrin clot (scab). Normal platelet values are 150,000-350,000. In some individuals, HIV infection itself causes a decrease in the number of platelets. Otherwise, drugs can also cause low platelet counts. Even though counts are considered low below 150,000, most people can survive without the threat of internal bleeding with counts above 50,000. On very rare occasions, the number of platelets present are adequate, but for unknown reasons they don't function correctly. Any malady involving ones platelets can be a potentially serious condition.

White Cell Differential - The white cell differential counts 100 white cells and differentiates them by type. This gives a percent of the different kinds of white cells in relation to one another. The three main types are: polymorphonuclear cells (or PMNs), lymphocytes, and monocytes. PMNs are increased during bacterial infections while lymphocytes are decreased with viral infections. Increased monocytes are sometimes seen in chronic infections. normal percent of PMNs is 55-80%. 25-33% is the normal number of lymphocytes, and 3-7% is normal for monocytes.

There are a wide range of blood chemistry tests which are done on individuals either routinely or for a specific reason. Some of the ones pertaining to HIV infection are mentioned below.

Cholesterol - Cholesterol levels, as mentioned earlier, are routinely decreased in HIV positive individuals. It's not understood why this occurs, but is thought to be related to altered metabolism. normal cholesterol levels are 150-250 mg/dl.

Amylase - amylase is an enzyme that is secreted in the mouth by the salivary glands and also in the pancreas. It can be an early warning sign of acute Pancreatitis when elevated. ddI can cause problems with the pancreas in a small number of patients taking the drug. Normal amylase levels are 25-125 milliunits/ml.

CPK - CPK or CK is an enzyme that's found in the brain and the muscles of the body. Strenuous exercise as well as a heart attack can cause increases in CPK. This makes clear the point of evaluating an abnormal test result in the context of other factors. Myopathy, dysfunction/distress with the muscles, can sometimes be confirmed with an elevated CPK. Myopathy is usually caused by HIV but can also be due to AZT, especially at higher dosages. Normal levels of this enzyme are 12-80 milliunits/ml (30 degrees) or 55-170 milliunits/ml (37 degrees). Values will be slightly lower for women.

Liver function Tests - Liver Function Tests include 5-6 individual tests which collectively can help determine the status of ones liver. elevated liver enzymes are most often caused by certain medications. The HIV infected population also has a high prevalence of hepatitis. at least 4 different viruses are known to cause hepatitis, all leading to increased liver function tests. Therefore compound factors can be at work. If liver enzymes are only moderately elevated, most providers will take a "wait and see" attitude, monitoring them over a period of a few weeks to a few months. However, if the elevation is quite high, the underlying factor must be found. this might very well be one of the medications that you're currently taking. The names of these liver function tests include SGOT, SGPT, alkaline phosphate, total bilirubin and LDH.

Kidney Functions - Two tests which measure kidney function are the BUN and Creatinine. The usefulness of these tests in an HIV infected individual usually relates to medications possibly toxic to the kidneys. Hence kidney function is monitored in this way. Foscarnet is an example of a drug which can cause renal toxicity. Normal BUN levels are 10-20 mg/dl. Normal levels of creatinine are 0.6-1.2 mg/dl.

Lymphocyte subsets - The category of lymphocyte subsets includes absolute counts and percentages of CD4 and CD8 cells as well as other parameters. Usually the number and percent of B cells is included and the number and percent of all lymphocytes (except those called "natural killer" or NK cells). Lymphocytes are broken down mainly into T and B cells. T cells are further divided into CD4(+) cells and CD8(+) cells. It is well known that HIV infection causes a slow, progressive decline in the number and percent of CD4(+) cells in most individuals. There are exceptions. Some individuals progress in their disease very rapidly and others don't seem to progress much at all after more than 12 or 13 years of infection. Normal CD4 counts are 400-1500. The role of CD8 cells is less clearly understood. Early on in the epidemic, high CD8 cell counts caused inversion of the CD4:CD8 ratio and was thought to adversely affect illness. Now it is generally believed that elevated CD8 cell counts are advantageous in the HIV positive individual as it's thought to indicate the body's ability to keep HIV somewhat constrained. Normal CD8 cell counts in an HIV negative individual are 275-780. How CD8 cells are beneficial is still being investigated.
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