Disease Detective: Diagnosing Rheumatic Disorders
One in 12 women and one in 20 men will develop a rheumatic disease at some point.1,2 Approximately 300,000 American children have a rheumatic disease.3 Regardless of the specialty or setting in which a health-care provider practices, an opportunity to care for a person with a rheumatic disease will likely occur during his or her career.
Many clinicians approach rheumatic disease with uncertainty. This trepidation is partly caused by the complex nature of the conditions encountered. Diagnosing and caring for those with rheumatic disease requires superb detective work.
Hearing what a patient says when obtaining a thorough history, observing telltale signs present during a physical examination, and evaluating results of appropriately selected ancillary tests (laboratory, radiographic, other) is similar to the work that a detective must do to solve a mystery. Knowing which details are most relevant is essential to providing the highest quality of care.
Comprehending the utility of rheumatology-specific lab tests can increase confidence in one's knowledge of the rheumatic diseases.
After a brief overview of system review labs, this article will primarily focus on three of the most commonly ordered rheumatology labs:
- Antinuclear antibody (ANA),
- Rheumatoid factor (RF)
- Anti-citrullinated peptide antibody (ACPA)
The article will provide answers to frequently posed questions regarding these common rheumatology serologies.
System Review Labs
Lab work serves a number of purposes (Table 1). Given the demands for quality and efficiency in the current health-care environment, it is vital that providers have specific purposes when ordering lab work.
|Table 1. The benefits of lab work
|Establishes a diagnosis
|Monitors disease activity, prognosis, or damage|
|Monitors drug or therapeutic toxicities|
|Establishes complications of the underlying disease process|
|Excludes alternative diagnoses or complications|
|Source: Bartlett SJ, ed. Clinical Care in the Rheumatic Diseases, 3rd ed. Atlanta, Ga.: Association of Rheumatology Health Professionals; 2006.|
Many rheumatic conditions are systemic diseases that can affect multiple organs. For this reason, system review laboratory tests, including complete blood counts, blood chemistries (with renal and hepatic function) and urinalysis, play an important role in the diagnosis and monitoring of persons with rheumatic conditions.
The ability to interpret these common laboratory studies and describe the results in layman's terms is a vital part of making appropriate and informed treatment recommendations.
Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are also helpful in diagnosing and monitoring those with rheumatic disease. Factors that may cause these acute-phase reactants to be elevated include autoimmune disease, infection, malignancy, pregnancy, anemia and obesity. Although nonspecific, ESR and CRP provide helpful information. Several tools that measure disease activity incorporate either the ESR or CRP as variables in their formulas.
In 1948, Hargraves first described lupus erythematosus (LE) cells in sera of patients with systemic lupus erythematosus (SLE).4 LE cells, phagocytes with ingested nuclear contents, were found in various body fluids, including pleural, pericardial, and peritoneal.
Various techniques for determining the presence of ANA in a patient's sera have evolved over time, but the value of ANA in diagnosing SLE and other autoimmune conditions remains unchanged. Although multiple subtypes of ANA exist (i.e., dsDNA, SS-A, SS-B, ENA, Scl-70), to remain within the scope of this article, only the more general ANA will be discussed.