1999, Volume 10, Number 1
Call Us With Your Questions About New Tests
David F. Keren, M.D.
Last week, a request to perform assays for interleukin 1 beta (ILß) and interleukin 6 (IL6) on a serum was brought to my attention. There are no FDA approved assays available for either analyte and the only laboratory we found that performs these assays is quite costly.
ILß and IL6 are cytokines. These are proteins released from cells that play a role in regulating the inflammatory response. ILß is important in the proliferation of T lymphocytes, whereas, IL6 is mainly involved in augmenting the production of acute phase reactant proteins (alpha-1 antitrypsin, alpha-1 acid glycoprotein, C-reactive protein, haptoglobin) and suppressing the production of albumin by hepatocytes.
Although both ILß and IL6 are interesting biologically functional molecules that have been the subject of innumerable research studies, neither has been proven to be useful in routine diagnostic work. Therefore, I contacted the clinician to review the clinical situation and see if there were more readily available assays that would help in his differential diagnosis.
His patient had osteoporosis and he was looking for evidence of inflammation as part of the process. Although the interleukins might be of research interest in cases such as this, they will not help in managing this patient. Further, the research assays one can purchase are costly and may display considerable variation from one research laboratory to another. For patients with osteoporosis, there are several diagnostically useful methods for collagen crosslinks and bone-specific alkaline phosphatase available to evaluate both bone formation and reabsorption.
To evaluate acute inflammation, I agree with a recent New England Journal of Medicine Article (Gabay & Kushner, NEJM 1999;340:448) that recommended the classic C-reactive protein assay for most conditions, or an erythrocyte sedimentation rate for patients with systemic lupus erythematosus. These assays are well-established early markers that are readily available, inexpensive and well controlled.
When new markers are described in the literature, they may or may not stand up to the test of time. For instance, 15 years ago, circulating immune complex assays were commonly performed for a wide variety of conditions. Today, they are considered worthless for routine diagnostic work, though still of some interest in selected research studies. Please feel free to call us at any time to discuss new assays that may be relevant to your patient care.
We are always eager to develop diagnostically useful tests, but temper our enthusiasm for new testing by requiring independent evidence that it will assist in the diagnostic process.