Testing times
Robert Fieldhouse’s simple guide to blood tests and
what they tell us about our health
Doctors
use a battery of blood tests to keep a watchful eye on how our bodies cope
with HIV infection. They measure chemicals in our blood to see how our heart,
liver, kidneys and pancreas are working and how our muscles and bones cope
with HIV and antiretroviral therapy.
Blood test results alert your doctor to new infections or the beginnings of
HIV medication side effects. They select from hundreds of individual tests
depending on the treatment you are on and your medical history.
CD4 TESTING
CD4 cells are a vital part of your immune system. They are attacked by HIV
making us more likely to catch opportunistic infectons. Your CD4 count tells
you how many you have in one cubic millimetre of blood and this indicates
how well your immune system is doing - the greater the number the better.
CD4 counts typically range between 600 and 1,200 in HIV negative people. A
number of factors including recent illness and vaccinations can skew CD4 test
results so if yours drop unexpectedly you may want to retest in two or three
weeks or once you are well again
You should have a CD4 test as soon as you are diagnosed and then every three
months. This helps you and your doctor monitor what HIV is doing to your body.
Ideally, have blood taken at the same time of day.
Absolute CD4 count
Less than 200 and you may need to start preventative therapies to ward of
certain infections. Right now doctors are debating if people with a CD4 count
less than 350 should be on treatment. If it’s higher you can probably
wait a while.
CD4
percentage
This shows you the proportion of your immune cells that are CD4 cells. It
is about 40 per cent in an HIV negative person. With HIV, the percentage declines
as our immune systems fall out of balance.
CD4/CD8 ratio
CD4 cells are ‘helper’ cells which co-ordinate the immune system
while CD8 cells are called ‘killer T cells’. In HIV negative people
these are usually balanced with one CD4 cell for ever CD8 cell. But in HIV
infection, CD8s rise as CD4s fall.
VIRAL LOAD TESTS
Viral load tests measure the amount of HIV in your blood. The higher your
viral load the more virus there is to attack your immune system.
Because viruses are so small, counting them is a complicated process and fluctuations
can occur. Only large changes, like 50,000 to 500,000, are significant. There
are two types, of test: PCR, the most common, and branched b-DNA. Ensure you
get the same kind of test each time and only compare like for like.
Viral load off treatment
A viral load less than 100,000 copies is considered low in people not on treatment.
But a high viral load in the millions is not uncommon when you have just been
exposed to HIV.
Viral load on treatment
The aim of treatment should be to get your viral load to below 50; this is
described as an undetectable viral load.
A new regimen should take a little over a month to get your vial load to undetectable,
depending on how high it was before you started therapy. If it does not drop
significantly and quickly enough this may be a cue to try another regimen.
DRUG RESISTANCE TESTING
Even at undetectable levels, HIV is still present in you blood and continues
to copy itself. As it does, tiny mistakes or mutations occur and new strains
of virus develop. Unfortunately for us, some of these mutated strains are
resistant to certain HIV meds and they become less and less effective.
Resistance testing tells you what mutations your HIV has developed and which
drugs it may have become resistant to. You should be offered a resistance
test when you are diagnosed and before starting treatment.
If you are on treatment and your viral load rises, or if you switch to a new
combo but your viral load fails to drop, you should be offered a resistance
test. If you have resistance, it may be time to change your meds.
You also need to keep resistance in mind when choosing a new combo, since
different drugs can cause different mutations. Some meds are more likely to
cause one of the mutations that can single handedly make you resistant to
a whole family of drugs; others may cause mutations that need to be present
in bigger numbers before they reduce the effectiveness of your drugs. Ask
your doc what alternatives you have if the combo you’re thinking of
taking should stop working.
TYPES OF RESISTANCE TEST
Two types of blood tests measure drug resistance: genotype and phenotype.
You need a viral load of at least 500 to 1,000 for either test to work. And
both should be taken, where possible, while you are still on your meds. Once
you come off the meds, HIV may revert to its natural, or ‘wild type’
making resistance more difficult to detect.
Genotypic resistance
Genotypic testing identifies which mutations your virus has developed. It
is cheaper and faster but doesn’t directly measure resistance, just
mutations likely to cause resistance.
Phenotypic
resistance
Phenotypic tells you how susceptible your HIV is likely to be to each drug.
It will directly measure the amount of resistance you have to a certain drug.
Samples of your virus are added to test tubes containing different HIV drugs
and the lab counts the number of copies your HIV makes in each tube. Resistance
is calculated by assessing how much of a drug it takes to reduce your HIV’s
replication by 50 percent.
Viral fitness
Many mutations make faulty or less ‘fit’ versions of the original
virus. Your HIV may have learned how to duck the drugs, but in the process
they may have weakened too much to successfully battle against your immune
system. A viral fitness test will tell you if your mutations are making your
HIV more or less fit.
The test measures your HIV’s ‘replicative capacity’; its
ability to make copies of itself. If your virus is resistant but unfit, your
doctor may keep you on a combo that otherwise may seem to be failing.
COMPLETE BLOOD COUNT
A complete blood count (CBC) counts all the different types of blood cells;
red ones, white ones and platelets. Levels of these can indicate common problems
like anaemia, pneumonia, bone-marrow disease or cancer. It can also indicate
side effects to HIV meds. This should be done as part of your regular bloods,
usually every three or four months.
White
blood cell count
White blood cells are the front line of your immune system. They are produced
in your bone marrow. A high white blood count suggests a battle is already
underway; a low count may be caused by the effects of HIV meds, HIV itself
or a bone-marrow problem. A normal count is between 3,500 and 11,000 per cubic
millimetre of blood.
Haemoglobin count
Haemoglobin helps red blood cells carry vital oxygen from your lungs to all
your other cells. As many as one in five people with HIV may have a low level
with women and black African people particularly vulnerable. Lack of haemoglobin
results in anaemia that causes fatigue, listlessness and shortness of breath.
Some people get anaemia from the effect of HIV on their blood cells. But most
get it because meds like AZT can cause anaemia. Drugs such as Procrit stimulate
red blood cell production and almost always give your haemoglobin the necessary
boost. People with HIV who are iron deficient may benefit from supplements
- but ask your doc first.
Platelets
Platelets stop wounds from bleeding by clotting the blood. People with HIV
are prone to low platelet counts (thrombocytopenia). The average count is
140,000 to 400,000 per microlitre; the risk of bleeding increases if it drops
below 40,000.
Haemocrit
Haematocrit measures what proportion of your blood is made up of red blood
cells.
A low result confirms anaemia; a high one could be from smoking, dehydration,
lung disease or certain tumors. For men, a healthy range is 39 to 50 percent;
for women, it is 36 to 46 percent.
BLOOD FATS AND YOUR HEART
People living with HIV commonly test low for ‘good’ HDL cholesterol
due to the HIV virus itself but sometimes from anabolic steroids use or insufficient
exercise. LDL cholesterol, the bad kind, clogs your arteries, and increases
your risk of heart disease. ‘Friendly’ HDL cholesterol acts as
an artery detergent, scrubbing them clean. Some HIV meds and HIV itself can
boost bad LDL; we still don’t know definitively which ones.
Triglycerides
These are the most common kind of fats we eat. At high levels they can be
associated with heart attacks and inflammation of the pancreas (pancreatitis).
People on protease inhibitors, in particular, need to keep an eye out for
this.
‘D’ drug monitoring
If you’re taking either of the ‘d’ drugs, d4T (Zerit) and
ddI (Videx), then two fat digesting enzymes, amylase and lipase secreted by
the pancreas, should also be monitored. Use of d4T is less common now and
you’re unlikely to take them together unless there is a real clinical
need.
BUN
Blood urea nitrogen (BUN) rises if you are dehydrated, have kidney or heart
failure or and underactive liver or thyroid. Anti-inflammatory steroids, a
high-protein diet and strenuous exercise could also be to blame. A drop in
BUN may reflect poor nutrition.
Creatine levels
These tell you how well your kidneys are filtering your blood. Look out for
false elevations from the pneumonia drug Bactrim or the muscle pumping powder
creatine.
LIVER FUNCTION TESTS
A healthy liver keeps your blood free of toxic compounds and helps your body
get the most from your HIV drugs. Around third of people living with HIV in
Europe are co-infected with hep C. You should be offered annual screening
for hep C (HCV) antibodies.
High liver function tests on HIV therapy may mean your HIV drugs are damaging
your liver. It may also mean you have been infected with hepatitis. If you
haven’t been vaccinated against hepatitis A and B, prioritise these
jabs at your next clinic visit.
Low
albumin
Albumin is the main protein in blood. Low levels suggests malnutrition, cirrhosis
(scarring of the liver) or hepatitis B, C or HIV drug toxicity.
Raised alkaline phosphate
This could signal an HIV med needs adjusting; disease; injury, liver inflammation
or strenuous muscle use.
Raised
ALT
Alanine aminotransferase (ALT) is an enzyme found mostly in the liver and
in smaller amounts in the kidneys, heart, and muscles. Under normal conditions,
ALT levels in the blood are low. When the liver is damaged, ALT is released
into the blood stream, usually before more obvious symptoms of liver damage
occur, such as jaundice (yellowing of the eyes and skin).
Raised AST
Aspartate aminotransferase (AST) is an enzyme found mostly in the heart and
liver, and to a lesser extent in other muscles. When liver or muscle cells
are injured, they release AST into the blood.
Raised
GGT
Gamma-glutamyl transpeptidase (GGT) is an enzyme highly sensitive to changes
in liver function. It is normally present in low levels but when the liver
is injured or obstructed, it rises. It is the most sensitive liver enzyme
in detecting bile duct problems.
PT test
Prothombin time (PT) measures how long the blood takes to clot. It can be
used to monitor treatment with medication that prevents blood clots forming
such as warfarin. An abnormal PT is often caused by liver disease or injury.
Raised
bilirubin
High bilirubin levels cause jaundice and may indicate hepatitis or other viral
infections. Some drugs, including the protease inhibitor atazanavir, can raise
bilirubin slightly, giving you have a yellow hue but without risk to your
health it seems.
