Last issue we looked at the two key immunological blood tests — CD4 count and viral load. But there’s more to your three-monthly blood tests than that. Biochemistry tests can spot illness, identify drug side effects and help you manage your health.
As well as CD4 count and viral load tests, people with HIV, especially those on treatment, should also have a range of other regular blood tests. These tests are grouped together under the general heading of biochemistry or haematology.
Regardless of which term your doctor prefers, the objective of these tests is to measure the levels of various chemicals and cells in the blood. Abnormalities or changes in these levels can alert your doctor to possible illness and treatment side effects.
It’s usual to have most of the tests below done every three months for positive people on treatment and those who have symptoms of HIV disease, or less often for those who do not have symptoms. Depending on your particular circumstances, your doctor may not do all the tests in this article, and may do others not described here. If you’re unsure about the meaning of any test result, the best person to explain it to you is always your doctor.
Reference intervals
The ‘reference interval’ or ‘normal range’ is usually shown on the laboratory report for each test performed. Every blood test has a reference interval into which 90% of the healthy population falls. These ‘normal’ values can vary depending on your age, sex, stage of HIV infection, other illnesses (including opportunistic infections) you may have, the medications you’re taking, or even the time of day the test was taken.
Because reference intervals are averages based on large numbers of people, they provide an excellent guide for interpreting your results, but they can’t take into account your individual body makeup. For this reason, it’s important to discuss any results which bother you with your doctor.
Reference intervals also vary from laboratory to laboratory, so the normal range given on your test report may be slightly different to the ranges given in this article. (The ranges in this article are those used by the SydPath laboratory at Sydney’s St Vincent’s Hospital).
Full Blood Count (FBC)
The Full Blood Count is a set of tests that measure the various different blood cells, including white cells, red cells and platelets. Other tests in the FBC measure haemoglobin, neutrophils and other blood components. The most important tests are described below.
Red Blood Cell (RBC) Count and Haemoglobin (Hb)
Red blood cells are produced in the bone marrow and are involved in carrying oxygen through the body. Inside each red cell, oxygen molecules attach themselves to molecules of the protein haemoglobin, which releases the oxygen when it is required by your organs or tissue.
Without enough red cells, or enough haemoglobin, your body can’t get the oxygen it needs. This condition is called a class=“glossary-term” href=”/glossary/term/402”>anaemia.
- The RBC Count measures the number of red cells in each millilitre of blood. The normal range for men is between 4.5 and 6.5 million cells/mL. For women the range is slightly lower (3.8-5.8).
- The haemoglobin count may be reported as grams per litre (g/L) or grams per decilitre (g/dL) of blood. You can convert between the two by multiplying or dividing by 10. Normal levels are 130-180 g/L (13-18 g/dL) for men and 115-165 g/L (11.5-16.5 g/dL) for women.
Many people with HIV have lower than average levels of red cells, and slightly decreased RBC counts may be no cause for alarm, even if they fall outside the reference interval.
Significantly reduced, or falling, RBC or haemoglobin counts, however, are a sign of anaemia, and should be investigated. Symptoms of anaemia include tiredness, fatigue, shortness of breath, and a pallid (pale) skin colour.
Anaemia may be a side effect of some HIV drugs (most commonly AZT, less commonly 3TC, d4T and some protease inhibitors), a side effect of certain other medications (especially the anti-CMV drugs cidofovir, ganciclovir and foscarnet), a sign of dietary problems (iron, vitamin B-12 and folic acid are all needed for production of red blood cells) or a sign of illness.
Most people with HIV will experience anaemia at some point. Because there are so many possible causes, because it can have a dramatic effect on your quality of life, and because some studies have found that HIV-positive people with persistent anaemia have lower survival rates, it’s important to work with your doctor to determine the cause and, where appropriate, treat anaemia.
Platelets
Platelets are blood cells that are essential for blood clotting. Platelet counts are expressed in thousands of platelets per cubic millimetre, with the normal range being 150 to 400. A low platelet count (*thrombocytopenia*) can be caused by HIV infection itself, and it has been reported as a (relatively uncommon) side effect of anti-HIV drugs.
Very low platelet counts (lower than 50) carry the risk of major bleeding and may be caused by drug reactions, autoimmune problems, vitamin B12 deficiency or folic acid deficiency.
White Blood Cell (WBC) Count
White Blood Cells, or leukocytes, which include the T cells, are key parts of the immune system. The normal range is 4-11 thousand cells per cubic millimetre.
Low counts (leukopenia) indicate an increased susceptibility to infection and may be a side effect of certain drugs (AZT, d4T, ddI, ddC, some PIs, rifabutin, gancyclovir), or may be caused by minor viral infections, HIV itself, stress, or opportunistic infections.
Neutrophils
Neutrophils are another type of white blood cell. The normal range is 2.0 to 7.5 thousand cells per cubic millimetre.
A low neutrophil count (*neutropenia*) indicates a lowering of the body’s immune defence against bacteria, and may be caused by medications (commonly 3TC, abacavir, AZT, ddC, FTC, rifabutin, cidofovir; less commonly most PIs, delavirdine, nevirapine), by HIV itself, or infection.
Electrolytes
These tests measure the levels of sodium, potassium, chloride and bicarbonate in the blood. Electrolytes are important in maintaining normal body functions such as heart function and muscle contraction. Abnormal electrolytes may be a sign of dehydration, especially if you’ve had diarrhoea or been vomiting.
Glucose
Glucose is a type of sugar. Ideally you must not eat or drink anything but water for several hours before the blood is taken for the test to be accurate. The normal ‘fasting’ range is 3.0 to 5.5 millimoles per litre (mmol/L).
Elevated glucose levels may indicate a class=“glossary-term” href=”/glossary/term/95”>diabetes, a class=“glossary-term” href=”/glossary/term/102”>liver disease or pancreatitis, all which are serious (but relatively rare) side effects of some antiretroviral drugs; further tests would be required to confirm a diagnosis. The protease inhibitor amprenavir and the anti-PCP drug intravenous pentamidine can also cause abnormally high glucose levels.
Testosterone
Many men with HIV have abnormally low levels (under 12 nmol/L) of the hormone testosterone. Symptoms of low testosterone may include fatigue, depression, loss of sex drive and wasting.
Kidney function
The kidneys eliminate excess water and waste products from the blood via urine. Two tests are used to measure kidney function — creatinine and urea, or blood urea nitrogen (*BUN*).
High levels of creatinine or urea may be a sign of dehydration or kidney disease. Tenofovir, T-20, some other antiretrovirals and other drugs (including the anti-CMV drug cidofovir) may be toxic to the kidneys.
Liver function
There are a large number of different markers used to assess liver function, including ALT (alanine transaminase), AST (aspartate transaminase), albumin, total protein, a class=“glossary-term” href=”/glossary/term/85”>bilirubin, ALP (alkaline phosphatase) and GGT (gamma-glutamyl transpepsidase). The normal ranges are shown in the table below.
| ALT | <30 units/L |
| AST | <30 units/L |
| albumin | 36-47 g/L |
| protein | 66-82 g/L |
| bilirubin | <18 µmol/L |
| ALP | 30-100 units/L |
| GGT | <35 units/L |
The liver metabolises carbohydrates, proteins and fats from the diet, and processes drugs so that they can be removed from the body. Hepatitis, HIV, alcohol, recreational drugs, some antivirals and some other medicines can all affect liver function. Elevated liver enzymes may also be indicative of liver disease, injury or tumours.
Abnormal liver enzyme levels are very common in people with HIV, but serious liver complications are rare.
High ALP levels with normal bilirubin may indicate serious disease such as MAC, CMV, histoplasmosis, drug toxicity or Kaposi’s Sarcoma. High bilirubin levels, usually accompanied by jaundice (yellowing of the skin and the whites of the eyes) can indicate hepatitis, bile duct obstruction and other liver problems.
Pancreas function
Amylase is an enzyme secreted by the salivary glands and the pancreas. Elevated amylase levels (over 100 units per litre) may be a sign of pancreatitis (inflammation of the pancreas), which, if untreated, may be very serious or even fatal. Pancreatitis is a rare side effect of some antiretroviral drugs, including ddI, ddC and d4T.
Lipids
Higher than normal levels of cholesterol and triglycerides are very common in people taking antiretroviral treatments, particularly protease inhibitors, and may carry an increased level of risk of developing heart disease.
Cholesterol and triglyceride levels are given in millimoles per litre (mmol/L). The normal range for cholesterol is under 4 mmol/L, for triglycerides under 2 mmol/L. Even if you are unable to keep your cholesterol and triglycerides within these ranges, getting them as low as possible is important, especially if you have other risk factors for heart disease such as smoking, high blood pressure or diabetes.
Reducing the amount of saturated fats in the diet (while being careful to maintain a healthy diet) can reduce lipid levels, and in some cases doctors may prescribe cholesterol-lowering drugs (statins).
Next issue: Part three — Resistance Tests and Therapeutic Drug Monitoring.
