There has been much debate about what constitutes a biomarker which has led to confusion in some areas.  However, this does not detract from their usefulness in many clinical situations.

A biomarker can be defined as a biological molecule found in blood, body fluids or tissues that is a sign of either normal or abnormal processes, or signs of a disease.  Biomarkers may be used to see how a body responds to treatment for a disease or condition.

Some biomarkers can be very specific, but most are more generic.  We believe that it is this lack of specificity that confers clinical value on biomarkers such as acute phase proteins (APPs).  Circulating concentrations of APPs like C-reactive protein (CRP) increase dramatically, often by several hundred-fold, and rapidly in response to numerous clinical conditions. Furthermore, they also drop very rapidly when the stimulus (disease state) is resolved.  Consequently, biomarkers such as CRP provide a good snapshot of either disease progression or resolution in near real-time.  Testing for CRP can now be rapidly and conveniently performed in the clinic.  These allow for timely and objective monitoring of treatment efficacy, indicating if it can be stopped or if treatment protocols require modification.

Many available tests are semiquantitative at best, and therefore do not allow monitoring of subtle changes during the course of treatment or periods of remission. Examples of such tests are lateral flow devices. These are helpful in making rapid diagnostic decisions, but they lack the precision needed for quantitative disease monitoring. On the other hand, the SPARCL^TM CRP assay is extremely sensitive and measures over a wide range of biomarker concentrations, making it an ideal method for disease monitoring.

The lack of specificity of CRP allows for numerous diseases, once diagnosed, to be monitored using only a single test.  The extreme sensitivity of the CRP test enables monitoring using only a small drop of blood which can be important for smaller breeds.  The need for such as small sample has allowed some practices to take a baseline CRP measurement from residual blood samples routinely taken for diagnostic purposes.  Ongoing longitudinal CRP measurements can then indicate treatment efficacy. Dependant on the animal’s diagnosis, urine or faecal samples can be collected by the owner and returned to the practice for monitoring purposes.

Examples.

CRP is produced by the liver and released into the blood in response to a wide range of localised or systemic inflammatory conditions.  Therein lies its value as a routine disease monitoring biomarker. A single test allows the clinician to objectively observe progress from many different inflammation inducing conditions.  If levels increase during or after treatment, this is a clear sign that treatment was not fully effective and alternative therapies or interventions are necessary. However, treatment induced return to a normal state will result in a dramatic drop in serum CRP levels.  Examples are:

• Monitoring antibiotic responses in a wide range of bacterial infections
• Monitoring steroid responses to various inflammatory conditions such as steroid responsive meningitis, inflammatory bowel disease and immune mediated polyarthritis
• Resolution of corrective surgical procedures

Multiple Marker Testing.

At PDx, we aim to introduce a range of different biomarker tests all based on the rapid SPARCL^TM luminescence platform. Some will be generic, such as CRP for monitoring purposes.  Others will be more specific to act as a diagnostic tool.  When the two are measured together during diagnostic workup, it should be possible to obtain rapid, in practice diagnostic decisions and monitor therapeutic progress from the outset of treatment.