In many parts of the world, medical providers care for their patients who have HIV/AIDS without the benefit of laboratory tests -- sometimes even the most basic ones. Fortunately, in the United States (and various other countries), medical providers almost always have available to them a wide range of diagnostic tools. Below are ten (plus three) of the most important ones.
Over time, the CD4 percent is a more stable measure of your immune system function because the total CD4 count is influenced by your white blood cell count at the moment your blood was drawn, a number that varies constantly. Nonetheless, by habit and tradition, health care providers have used the total CD4 cell count for key decisions, such as starting HIV meds or preventive therapy for opportunistic infections, like PCP (Pneumocystis pneumonia).
There are two versions of the most commonly used test, the Roche assay, and both have established cut-off values for the upper limit of how much virus can be detected and the lower limit, which is referred to as "undetectable" virus. Note that "undetectable" means the amount of HIV is less than the technical ability of the test to detect it and does not mean that HIV is not present.
The Amplicor version of the viral load assay has a low end cut-off of "less than 400 copies/ml" of HIV RNA/ml and an upper limit of "greater than 750,000 copies/ml." The Ultrasensitive test has a low end cut-off of "less than 50 copies of HIV RNA/ml" and an upper limit of "greater than 75,000 copies/ml." The significance of the difference between these two tests is that the Amplicor test is more accurate at higher viral loads and the Ultrasensitive test is more accurate at the low end of viral loads.
It is useful to do the Amplicor test when someone is first evaluated for HIV disease because it is valuable to know before starting treatment if the viral load is in the thousands, hundreds of thousands, or millions. Once someone is on HIV treatment and is doing well, it is more useful to use the Ultrasensitive test, given that the goal is to get the viral load as low as possible and this test is able to detect lower levels of virus in the blood.
There are other types of viral load tests, such as the branched DNA (bDNA) assay, that are sometimes used. There are various technologies but the measurement principles, with cut-offs for the upper and lower limits, are similar to what is described for the RNA PCR tests above.
Liver Function Tests (LFTs): These tests measure some key functions of the liver, a complex organ that does many important tasks in the body. The liver manufactures proteins that are essential to blood-clotting and to keeping fluid in your bloodstream instead of leaking out into your tissues and causing swelling (edema). The liver breaks down most environmental poisons (toxins) and drugs to rid the body of them. It also forms bile, which is important for digestion.
Amino aspartate transaminase (AST, formerly SGOT) and alanine aspartate transaminase (ALT, formerly SGPT) are key enzymes that indicate how well liver cells (hepatocytes) are functioning. The levels of an enzyme called alkaline phosphatase and a protein by-product called bilirubin indicate how well the production and excretion of bile is going. Albumin, a protein made in the liver, is critical for keeping fluid in the bloodstream and is an overall measure of nutritional status.
Liver function can be damaged by alcohol abuse, environmental toxins (including street drugs), viral infection of the liver (viral hepatitis) and a long list of diseases. Since people with HIV sometimes also have chronic hepatitis B or C, drink too much, or experience liver damage (hepatotoxicity) from medications, LFTs are important to monitor.
Kidney (renal) function tests: These tests measure how well your kidneys are doing their primary job, which is to rid the body of protein waste (blood urea nitrogen, or BUN) and regulate blood volume by filtering out the waste and extra water to form urine. The two main kidney function tests look at the level of waste as a way to measure how efficiently your kidneys are operating. These tests can provide clues that someone might have HIV-associated nephropathy (HIVAN) or kidney malfunction due to other causes, such as dehydration or drug toxicity.
Since some drugs are excreted from the body by the kidneys, dose adjustments need to be made when a person develops altered kidney function. Awareness of kidney dysfunction is also important when selecting an ARV regimen because some medications, like Viread, are not preferred for someone with underlying kidney disease.
Kidney function should be checked when someone enters HIV care. Thereafter, people at high risk of developing kidney disease (primarily African Americans and diabetics or people with a family history of diabetes) should have their kidney function checked at regular intervals. Routine checks are also recommended for people on ARV therapy.
There are a number of blood tests for syphilis (RPR, FTA, syphilis IgG), but the type of test is less important than the fact that everyone with HIV should have one upon entering HIV care and women who become pregnant should have one. After that, screening depends on risk -- people who are at higher risk of exposure through unprotected sex, especially with multiple partners, may need to be screened regularly. Several outbreaks around the country among men who have sex with men have occurred over the past several years. Sex workers, incarcerated individuals, and people with other sexually transmitted infections are also at high risk.
Some HIV medicines are active against hepatitis B, so it is important to craft an ARV regimen that will adequately treat both HIV and HBV at the same time. Hepatitis C currently requires treatment with two drugs that do not control HIV, and this therapy can be pretty challenging. However, depending on virus type and other factors, treatment can be very effective.
In addition to HBV and HCV, it is also important to test your blood for proteins that are protective (called antibodies) to hepatitis A (HAV). There is no chronic form of hepatitis A, but if you already have chronic liver disease from hepatitis B or C, you can get much sicker from hepatitis A than someone who doesn't have HBV or HCV because you already have some liver damage. Since there are vaccines available for hepatitis A and B (but not, unfortunately, for hepatitis C), these should be offered to every HIV-positive person whose blood tests show no prior exposure to these viruses.
Both genotypes and phenotypes are done on a blood sample. Genotypes, which are simpler, faster, and cheaper to perform, identify changes in particular viral genes that are associated with reduced or no response to specific drugs. Phenotypes, which are more complicated, time-consuming, and expensive to perform, test how well your HIV grows in the presence of different concentrations of HIV drugs.
Genotypes may be more than adequate for early resistance because they look at how much resistance the virus has compared to virus with no resistance; phenotypes have some advantages for people with extensive resistance because they can indicate how well the virus responds to individual drugs. The phenotype results can be especially useful when there are no "new" drugs available to someone and the only option is a "salvage" regimen of drugs to which the virus is still susceptible.
In the most difficult cases, both tests add information of value. Cost can limit the availability of these tests, especially the phenotype.
To be accurate, lipid testing must be done in the "fasted" state -- no food (or drink, except water or diet soda or plain tea or black coffee -- any drink without calories) for a minimum of eight hours, ideally 10 to 12. Fasting lipids include four separate measurements of different forms of fats that circulate in your blood: total cholesterol, high-density lipoprotein (HDL, or "good cholesterol"), low-density lipoprotein (LDL, or "bad cholesterol"), and triglycerides.
High levels of HDL protect you against heart disease caused by clogged arteries in your heart (atherosclerotic heart disease). Unfortunately, high levels of the other fats are associated with an increased risk for heart disease. Lipid levels can be lowered with lifestyle changes, but some people may also have to take lipid-lowering drugs in addition to a diet change and other interventions.
Cervical cancer is caused by infection with certain strains of human papillomavirus (HPV). Cervical cancer is a real threat to HIV-positive women, especially at lower CD4 counts, and became part of the case definition of AIDS in 1993. If caught early, it can be cured.
Anal Pap smears are still not standard of care due to limitations of the test and because an expert is needed to accurately analyze the results. The wealth of data that exists for cervical Pap smears does not exist for anal Paps, so questions remain about its reliability and predictability as a screening tool. In some centers, anal Paps have been an effective way to screen for anal carcinoma, but many centers lack health care providers and pathologists (the doctors who interpret Pap smears) who can perform this test reliably.
This test was developed initially for men who have sex with men, thought to be susceptible to anal carcinoma because of sexually transmitted HPV infection. However, women can also benefit from such a test, even if they have not had anal intercourse.
The guidelines for performing these screening tests are the same as those for HIVnegative individuals.
Judith Feinberg, MD, is a clinician and Professor of Medicine at the University of Cincinnati, where she is also the Director of the AIDS Clinical Trials Unit. Dr. Feinberg is an American Academy of HIV Medicine (AAHIVM)-credentialed HIV Specialist.
Additional Tests, When a Closer Inspection Is Warranted