Serum or plasma is used to determine the concentration of hormones or therapeutic drugs obtained from the patient’s blood. However, some of these chemical species tend to bind to proteins in the blood system thereby rendering them inactive. Only the unbound or “free” chemical species are biologically active. Tests for hormone and therapeutic drug levels are usually performed using immunoassays performed on laboratory immunoanalyzers. With the exception given below, no immunoassay is capable of discriminating the free drugs/hormones from the bound drugs/hormones. In order to measure the “free” drug/hormone, an additional manual step of separating the protein-free fraction from the sample must be taken. This is done by a process that incorporates either equilibrium dialysis or centrifugation. About eighteen hours are required to perform equilibrium dialysis, and thirty minutes are required for centrifugation to separate protein-free serum/plasma, referred to as a serum/plasma ultra-filtrate.
In 1976, the first commercial immunoassay designed specifically to measure “free” thyroid hormone became available. The availability of “free” thyroid hormone measurement revolutionized the way thyroid disorders (occurs second to diabetes in endocrine disorders) are diagnosed and treated, and today it will be difficult to find a laboratory that measures “total” thyroid hormone. Development of immunoassays for “free” therapeutic drugs and hormones are difficult and expensive. The ChroMedX alternative is to rapidly modify the sample in a disposable cartridge that can be presented to the existing immunoanalyzer.
The ChroMedX "AUF" (Automated UltraFiltration) cartridge provides a simple inexpensive way of preparing samples for analysis of free hormones and therapeutic drugs in a matter of minutes. The cartridge can be part of a fully automated immunoassay system, a stand-alone processing workstation or as a simple manual sample preparation procedure. The "AUF" technology employs a novel automated system of ultrafiltration which replaces the existing centrifugation techniques that are manual and time consuming. The cartridge contains both a bundle of hollow fiber membranes and an innovative dead-end air chamber. When a serum/plasma sample is injected into the cartridge by a positive displacement pipette, the dead-end chamber acts as a spring and allows multiple passes of the serum/plasma over the hollow fiber membranes, thereby unplugging the membrane pores. Samples, prepared using the "AUF", are free of chemical species bound to proteins and thus the measurement yields only the free hormone or drug. The rapidity and automation of the "AUF" technology promises to alter the way therapeutic drugs are monitored, and the way hormone-related disorders are diagnosed and treated. Proof of concept for this technology has been demonstrated by ChroMedX. The ChroMedX technologies are protected by issued and pending patents.
Table I shows results of proof of concept testing of the "AUF" cartridge. It can be seen from the table that the key electrolytes sodium, potassium and chloride, which do not bind to proteins are present close to their original levels prior to ultrafiltration. Proteins are shown to have been completely eliminated from the ultrafiltrate and both calcium and cortisol, which are partially bound to proteins, are at their predicted values in the ultrafiltrate.