Value of Laboratory Monitoring

by Dr Anuradha Venugopalan

The importance of laboratory tests in patients on treatment for most rheumatic diseases lies in the early identification of potentially harmful organ damage or in the assurance of the continuing safety of the applied drugs. Nevertheless, some abnormalities are of acutely life-threatening potential. So reducing frequencies of laboratory examinations could be an indication of higher risk for serious toxicity.

Whereas lack or loss of efficacy and clinical side effects are usually associated with characteristic clinical symptoms, laboratory abnormalities very often lack individual correlates, impeding judgment of the irrelevance. Furthermore, the predictive value of such abnormalities has not yet been established. However, laboratory testing or adverse events is performed on a regular basis in patients with RA because it may reduce patients' risk of side effects by allowing early recognition of such events, or reassure the physician that no side effect has actually occurred.

Clinically important laboratory abnormalities that have therapeutic consequences are done within the first 4 months of treatment and all are not required thereafter. Thus, using a rational and evidence-based strategy, costs for laboratory monitoring during therapy can be highly reduced. With newer therapies emerging, it is important to understand the need for types and frequencies of laboratory tests for these new agents.

Laboratory monitoring helps determine effectiveness of therapy often combined with a validated response measure in addition to monitoring the rheumatic disease. This article covers the blood tests used for general monitoring of rheumatology patients on disease modifying drugs (including biologic therapies).

Which blood tests would normally be used for monitoring when on DMARDs? Depending on the drug prescribed, tests and frequency may vary, but will commonly include: Erythrocyte Sedementation Rate, C-reactive Protein, Liver Function Tests, Haemogram, also known as CBC (Complete Blood Count: covering red cells, white cells and platelets), blood chemistry (especially monitoring effects on the liver and kidney) and Urine routine Examination.

The erythrocyte sedimentation rate (ESR) The ESR measures the degree of inflammation in the joints. Blood is taken and placed in a small, thin graduated tube and the distance the red blood cells settle in one hour is measured. The more rapidly the red cells settle the more inflammation in the joints. One of the aims of treatment is to reduce the ESR to normal levels.

The C reactive protein (CRP)

The CRP also measures the degree of inflammation in the joints. The CRP is a protein produced in the liver when there is inflammation anywhere in the body. Special techniques have to be used to measure the CRP. The more inflammation in the joints, the higher the CRP. The CRP is a more sensitive measure of inflammation than the ESR. This is because in the normal situation there is very little if any CRP in the blood.

In addition to CRP and ESR, the following may also be used in the continued monitoring of your RA:

A full blood count

This includes the hemoglobin (Hb) which will indicate whether or not you are anemic. A slightly low Hb is not uncommon in patients with active RA but a low Hb could also indicate other problems such as bleeding or a deficiency of iron and/or other vitamins (vitamin B12, folate and folic acid in particular). These possibilities will be investigated as necessary by your doctor.

Liver function tests

Liver function abnormalities are also a common feature of drug toxicity/allergy as well as indicating how healthy the liver is in dealing with drugs. Most drugs are broken down in the liver and abnormalities of the liver can lead to problems with handling of the drug in the circulation once it has been absorbed. Blood tests commonly included are Liver enzymes (AST/ALT), serum proteins, Bilirubin and Alkaline phosphatase. The entire panel should be done at baseline. ALT also called SGPT can be done at the follow-up visits.

Kidney function tests

Kidney function is important because many of the drugs used to treat RA can affect kidney function, including anti-inflammatory drugs and also some disease modifying anti-rheumatic drugs (DMARDs). Because many drugs are excreted through the kidneys it is important to know that kidney function is normal because any evidence of kidney failure can lead to a increase of drugs and may require a reduction in dosage. The common tests include Blood Urea and Creatinine levels.

At baseline CBC, ESR, Urine routine examination, liver function tests (LFTs) and kidney function tests are performed. Among other routine diagnostic testing, rheumatoid factor and anti- CCP, Antinuclear antibody and sometimes anti-ds DNA tests are done at baseline. CBC, ESR, ALT and urine routine examination is done every 2–4 weeks for the first 3 months, then every 3 months.

B Cell counts (commonly CD19) are done at baseline and at the end of every 3 months in case of patients receiving biologic Rituximab.

People do have a moderately increased risk of infection, especially in the first three months after starting treatment. Most of these infections are common in the general population, such as chest infections and skin infections (e.g. cellulitis). Anti-TNF therapy is also associated with an increased risk of tuberculosis (TB). Because we know this, we can take steps to minimise those risks. For example, people are screened for TB before starting treatment. Commonly performed tests are tuberculin skin test (TST) and TB-Gold assay also known as interferon-gamma release assay (IGRA). Tests for Hepatitis B and Hepatitis C virus must also be considered at baseline. HIV screening should also be considered in patients at risk.

The sooner you get the right treatment, the less likely you will suffer long-term joint damage. Your doctor can't literally feel your pain, but he or she could help ease it by using formal tools to track your disease activity. Laboratory tests can be reduced substantially in patients receiving appropriate therapy. In consequence, costs can decrease significantly without oversight of adverse events.