Laboratory Investigations in Rheumatology

Dr.Wessam El Gendy MDProf. of Clinical pathology

Systemic Lupus erythematosis Scleroderma Polymyositis/Dermatomyositis Rheumatoid Arthritis

Laboratory test results help diagnose monitor disease course predict disease outcome assess the response to therapy and gain insight into disease etiology or

pathogenesis.

Systemic Lupus ErythematosisSLE

There are many laboratory tests which aid the physician in making a lupus diagnosis.

Routine clinical tests which suggest that the person has an active systemic disease.

Sedimentation rate (ESR) and CRP (C-reactive protein) binding, both of which are frequently elevated in inflammation from any cause

Serum protein electrophoresis which may reveal increased gamma globulin and decreased albumin

Routine blood counts which may reveal anemia and low platelet and white cell counts.

Routine chemistry panels which may reveal– kidney involvement ;serum blood urea nitrogen

and creatinine– abnormalities of liver function tests– increased muscle enzymes (such as CPK) if

muscle involvement is present.

Immunological Tests in SLE

Anti-nuclear antibody test (ANA) to determine if autoantibodies to cell nuclei are present in the blood

Anti-DNA antibody test to determine if there are antibodies to the genetic material in the cell

Anti-Sm antibody test to determine if there are antibodies to Sm, which is a ribonucleoprotein found in the cell nucleus

Serum complement test to examine the total level of a group of proteins which can be consumed in immune reactions.

The Antinuclear Antibody (ANA or FANA) Test

The immunofluorescent antinuclear antibody (ANA or FANA) test is positive in almost all individuals with systemic lupus (97 percent), and is the most sensitive diagnostic test currently available for confirming the diagnosis of systemic lupus when accompanied by typical clinical findings.

Anti-nuclear AbANA

While the ANA is often positive in connective tissue diseases, it is also often positive in other non-autoimmune diseases such as:

1. Infectious disease (e.g. EBV, and viral hepatitis)2. Neoplastic diseases (e.g. leukemia, lymphoma,

melanoma, and other solid tumors), 3. other diseases such as primary biliary cirrhosis.

A significant number of healthy individuals may have a positive ANA.

However, positive ANAs in these non connective tissue diseases usually occur at a lower titre

Following patient progress?

ANA titers do not correlate with disease activity and the practice of ordering this test to monitor the course of SLE should be abandoned.

Expression of ANA Results.

If the patient has an ANA of 1:40 probably there is nothing.

If the ANA is 1:80 you need to investigate the case.

If the ANA is 1:160 or higher, rheumatologist should take a look – not all of them will have something, but some will.

"Does ANA-negative lupus exist "

"ANA-negative" person should be re-evaluated using: anti-Sm, anti-Ro, anti-RNP as well as clinical criteria.

However, systemic lupus erythematosus (SLE) is rarely, if ever, present when an ANA test is negative.

Test is overly sensitive 95%; not diagnostic without clinical features

Other Autoantibodies in Lupus

Antibodies to DNA Antibodies to histones  Antibodies to the Sm antigen  Antibodies to RNP (ribonucleoprotein)  Antibodies to Ro/SS-A Antibodies to Jo-1 are associated with

polymyositis.

Antibodies to PM-Scl are associated with certain cases of polymyositis that also have features of scleroderma.

Antibodies to Scl-70 are found in people with a generalized form of scleroderma.

Antibodies to the centromere

Following patient progress:

Most autoantibodies (RF, ANA , ENA [extractable nuclear antigen], anti-Jo-1, etc) do not vary with disease flare-ups and remissions and need be ordered only once during the diagnostic work-up.

Follow up of SLE

Complete blood count: anemia, thrombocytopenia, neutropenia

ESR & CRP Anti-ds DNA Serum complement Anti-cardiolipin Ab/ lupus anticoagulant in

cases with recurrent abortions or thrombosis

Screening

With few exceptions, broad-based screening tests are generally not recommended in the absence of suggestive history and/or physical findings because false-positive rates may be high.

Methodology

Immunoflurescence ELISA Immunoblot

Rheumatoid Arthritis

There is no single test that can be used to diagnose rheumatoid arthritis; it is a diagnosis that is made through clinical evaluation with the assistance of laboratory and non-laboratory testing.

Lab – Evidence of Inflammation

Acute phase response CRP Erythrocyte sedimentation rate

Laboratory investigations in Rheumatoid Arthritis

Complete blood count CBC Erythrocyte sedimentation rate (ESR) &

C-reactive protein (CRP) Rheumatoid factor (RF)• Anti-cyclic citrullinated peptide (CCP)

“Rheumatoid factor”

“Rheumatoid factor” is a misnomer; it confers a specificity to this test that is not deserved.

Rheumatoid factors are immunoglobulin M antibodies directed against the Fc (constant) region of the immunoglobulin G molecule

Rheumatoid factor in Rheumatoid Arthritis

Negative in 30 percent of patients early in illness

If initially negative, repeat 6 - 12 months after disease onset

Not an accurate measure of disease progression.

Non-Rheumatic Conditions

Aging

HCV Infection: bacterial endocarditis, liver

disease, tuberculosis, syphilis, viral infections (especially mumps, rubella and influenza), parasitic diseases

Pulmonary disease: sarcoidosis, interstitial pulmonary fibrosis, silicosis, asbestosis

Miscellaneous diseases: primary biliary

cirrhosis, malignancy (especially leukemia and

colon cancer)

Conditions Associated with a Positive Rheumatoid Factor Test

Rheumatoid arthritis (50 to 90%) Systemic lupus erythematosus (15 to 35%) Sjögren's syndrome (75 to 95%) Systemic sclerosis (20 to 30%) Cryoglobulinemia (40 to 100%) Mixed connective tissue disease (50 to 60%)

Methodology

Its presence can be detected with a wide variety of techniques (e.g., agglutination of sheep red blood cells, latex particles coated with human immunoglobulin G, enzyme linked immunosorbent assay or nephelometry).

Unfortunately,the measurement is not standardized in many laboratories.

Rheumatoid factor is present in most people at very low levels, but higher levels are present in 5%–10% of the population, and this percentage rises with age.

Anti-CCP

Anti-cyclic citrullinated peptide Specificity = 90% Sensitivity = 50-80%

Anticyclic citrullinated peptideAnti-CCP

Tends to correlate well with disease progression

Increases sensitivity when used in combination with rheumatoid factor

More specific than rheumatoid factor (90 versus 80 percent);

If present in such a patient at a moderate to high level, it not only confirms the diagnosis but also may indicate that the patient is at increased risk for damage to the joints.

Low levels of this antibody are less significant.

Anti-CCP

Can detect approximately 80% of all RA patients, but is rarely positive in non-RA patients, giving it a specificity of around 98%.

In addition, ACP antibodies can be often detected in early stages of the disease, or even before disease onset.

Flow chartRF

Anti-CCP

RF –iveAnti-CCP –iveVery unlikely

RF –iveAnti-CCP +ive

Early RA

RF +iveAnti-CCP +ive

Typical presentation

RF +iveAnti-CCP –ive

RA or infection

Interpretation

The physician must be aware of the sensitivity and specificity of each test. Tests with low sensitivity but high specificity are helpful only if positive, whereas tests with low specificity should not be ordered in the absence of a high diagnostic suspicion

The clinical laboratory shouldclearly state the type of immunologicprocedure performed

Define the reference range when including the cut-off values and indicate what percent of the normal population is included in the reference range.

Lab investigations of Lupus Nephritis

Monitoring with regular urinalysis & serum creatinine Screen all pts with proteinuria for ANA Anti ds DNA

In about 60% with SLE Levels often reflect disease activity Decreases with Rx ( ANA remains positive)

Serum complement

Anti-phospholipid antibodies

Sjogren Syndrome Diagnostic Criteria

Presence of anti-Ro/SS-A (60%), anti-La/SS-b (30%), antinuclear antibodies, or rheumatoid factor.

Polymyositis/Dermatomyositis

Blood testing usually (but not always) reveals abnormally high levels of muscle enzymes, CPK or creatinine phosphokinase, aldolase, SGOT, SGPT, and LDH.

These enzymes are released into the blood by muscle that is being damaged by inflammation. They can also be used as measures of the activity of the inflammation.

Other routine blood and urine tests can also look for internal organ abnormalities.