For the growing immunodiagnostics business, the news about rapidly rising health care costs is not all bad.

"Immunodiagnostics is the highest-growth segment of diagnostics, and diagnostics is the highest-growth segment of health care," according to Jack Schuler, vice president of Abbott Laboratories, the current leader in the field.

"If you look at the past 15 years, the growth of immunodiagnostics has been explosive," said Richard Flaherty, director of diagnostic standards and scientific affairs for the Health Industry Manufacturers Association. "The scientific advances in the area have been more pronounced than in any other area of the laboratory."

"Certainly our ability to measure materials in much smaller amounts and measure things we haven't been able to measure before, and do it more sensitively, has grown," Flaherty said.

A high-technology field still in its infancy, immunodiagnostics involves using the relationship between antigens, which are produced by every disease or toxin (and also by some of the foods we eat) that invades the body and the specific antibodies produced in reaction to those antigens for diagnosis. It provides more specific results than previous diagnostic methods--generally chemical tests, culture growth and hematology.

Those antigens and antibodies will attach to each other in a "lock-and-key" relationship. An antibody for hepatitis, for instance, will attach--without fail--to an antigen for hepatitis, even if there is only one such antigen surrounded by thousands of other kinds of antigens. As a result, the presence of an antibody for hepatitis can produce an infallible answer to the question of whether the disease is present, even if there are no other signs.

Mounting concern about medical costs are expected to fuel additional growth by increasing emphasis on diagnostics as a method to detect diseases early. Boosters of the industry argue that early diagnosis can avoid some of the high treatment costs associated with diseases in their more advanced stages, but others argue that early diagnosis may not produce a major, accompanying reduction in treatment costs.

Whatever the arguments about the long-term medical cost implications of immunodiagnostics, the rate of growth of the industry so far has outstripped growth in most other industries.

The growth rate for diagnostics as measured by revenue has been about 14 percent a year over the past 10 years, with the immunodiagnostics segment growing at almost double that rate--roughly 28 percent a year. By contrast, the average annual growth rate for the gross national product for the past 10 years was 2.3 percent.

With the prospects for enormous growth, companies are scrambling for leadership in the field, one in which the United States has a head start, with the same fervor that rocked Silicon Valley in the 1950s.

"I was with Texas Instruments when we were bringing the integrated circuit into the world, and I thought I would never see anything like that again," said Schuler. "This is much more wild than the introduction of the semiconductor, and there's also an element that what we're doing is meaningful."

Immunodiagnostics tests usually are performed with blood or urine samples, but go beyond earlier tests that generally either tested for chemical components such as glucose or iron or counted white or red blood cells.

One of several ways in which such tests are done is to coat a bead with a large number of antibodies to look for a specific antigen. If the bead is immersed in a blood sample where that antigen is present, it will attach to the antibody. If the bead then is resubmerged in a pool of antibodies with markers, a second antibody will attach to the tell-tale antigen.

Instruments read the diagnosis by looking for different types of markers, such as radioactive markers that emit a signal or markers that change color when an antigen and antibody attach.

Despite its relative newness as a diagnostic tool, immunodiagnostics accounts for nearly 20 percent of all medical tests, according to Larry N. Feinberg, vice president of Dean Witter Reynolds Inc. "I would look for it over the next five years or so to grow to 50 percent," he said.

Recent lifespan improvements "are a real measure of what diagnostics have been able to do," said Donald C. Sutherland, director of the clinical and instrument systems division of E. I. du Pont de Nemours & Co. "Immunoassays the tests through which immunodiagnoses are done turn out to be really the only way to stretch into the directions in which we are going now," he said. Those directions involve finding evidence of disease in smaller and harder-to-find concentrations, he added.

Tests now being performed regularly by immunodiagnostics include diagnosis for hepatitis, hormonal tests, cancer monitoring, tests for sexually transmitted diseases and therapeutic drug monitoring, which helps health care providers keep drug dosages at an optimum level, a concern particularly with drugs that can be toxic at too high concentrations.

One illustration of the specificity of immunoassays is its usefulness in detecting the presence of theophylline, an anti-asthmatic drug. The chemical structure of theophylline is very close to that of caffeine, "which is ubiquitous," according to Robert J. Molz, manager of research and development for the clinical and instrument systems division of Du Pont.

Using chemical means to detect the presence of theophylline was difficult, but antibodies "completely ignore the caffeine" and home in on the drug, Molz said.

The big prospective markets for immunodiagnostics are for early diagnosis of cancer and heart disease, the nation's biggest killers; succeess there could generate a multibillion-dollar business.

Despite considerable emphasis on finding the tools to diagnose these illnesses early, the search to date has not been enormously fruitful. As easy as it is to use antigens and antibodies to find each other once they are identified, making that initial identification is enormously difficult, needle-in-a-haystack research.

"If I had to guess, the Nobel Prizes for finding the keys to early diagnosis of major life-threatening diseases such as cancer and heart disease are not going to be won at Abbott but in a university laboratory. It's so random and it's so low-probability," Abbott's Schuler said.

Still another reason why academic researchers, rather than industrial researchers, may find the key is that "you're not going to get a patent on a biological product," Schuler said. "As soon as you find a marker, your competitors are going to say 'thank you very much,' " said Schuler.

In addition to market expansion that results from the discovery of new tests, the market is expected to expand as companies discover ways to move the tests closer to the users. Developing tests that can be performed in a doctor's office or at home will make more testing likely.

"The best example of what happens with the home market is pregnancy tests," said Robert Galen, chairman of the Department of Biochemistry at the Cleveland Clinic Foundation. "In no time at all, more tests wound up being performed at home than in the labs," although there was no real drop-off in the quantity of laboratory tests. "It's an incremental market."

According to both analysts and industry officials, the key to dominating the industry is to be big enough to market both the instrumentation for performing immunoassays and the reagents--the antigens and antibodies--that produce the diagnosis.

"It's like the razor blade companies which almost give away the razors to get the razor blade business," said Feinberg of Dean Witter Reynolds. "The real profit is in the reagents, not the instruments."

A big Du Pont product is the aca clinical analyzer, a computerized system that produces rapid diagnostic results. A new, smaller version of the aca that can be used in group practices and small hospitals is one of the most successful instruments ever introduced by Du Pont, according to company officials.

Currently only eight of the 50 tests the aca performs are based on immunoassays, but company officials expect that the tests they add to the machine's capacity will increase that proportion substantially. "This is clearly the most important research area for us," said Molz.

Both because of a desire to get users accustomed to their instruments and also to capture hospital spending before concerns about health care costs cut off those dollars, companies are willing to go to great lengths to make their products affordable, even giving the machines to labs that will buy the rest of the system, Galen said.

"Ten years ago, you never saw that kind of pressure to move equipment," he said. "It's kind of fun to be a laboratory director, because it's like Christmas."

Other factors expected to be critical in determining the winners in the consolidation in the industry are a company's ability to market worldwide, and to spend a lot of money on research and development.

Approximately 150 companies worldwide are in the fray now, according to industry analysts. In addition to Abbot and Du Pont, they include Syva, a division of Syntex Co.; Smith Kline Beckman, Centocor Inc.; Hybritech Inc.; Genetic Systems; Eastman Kodak Co.; Johnson & Johnson; the Technicon division of Revlon; American Hospital Supply Corp.; and Baxter Travenol Laboratories.

Part of the excitement about immunodiagnostics results from its nature: It is a high-tech, biotechnological industry that is one of the first to move from the pie-in-the-sky-by-and-by stage to realization. "It's the first wave of biotechnology to be commercialized," said Feinberg. "I'm looking for it to really take off."