Small measurement uncertainties in clinical laboratory tests can add large amounts to health care costs, according to a newly released study commissioned by the National Institute of Standards and Technology (NIST)
The study, conducted by RTI International (Research Triangle Park, N.C.) and the Mayo Clinic (Rochester, Minn.), estimates that calibration errors in measurements of calcium levels in blood may add between $60 million and $199 million to U.S. health care costs annually. High calcium levels can be a symptom of diseases such as cancer and thyroid disorders.
Accurate measurements are critical because calcium levels in healthy people fall within a narrow range, between 8.9 to 10.1 milligrams (mg) per deciliter (dL). Through interviews with laboratory managers and equipment manufacturers, the researchers estimated that results for up to 15 percent of calcium laboratory tests contain calibration errors of between 0.1 and 0.5 mg per dL. This means that some results that fall in the center of the "normal" range, say 9.7 mg/dL, may in fact be for patient samples with elevated calcium, defined as 10.2 mg/dL and above. At the same time, patients with measured values above the threshold, but who actually have normal calcium levels, may receive unnecessary follow-up procedures such as hormone measurements and chest X-rays.
The study analyzed data for more than 89,000 patients receiving serum calcium tests at the Mayo Clinic from 1998 to 1999. It found that calibration errors added between $8 and $89 per patient to the health care costs of approximately 3.55 million patients.
Major sources of calibration error include differences in analysis methods used by different laboratory instruments, lot-to-lot variations in calibration materials, and lack of "traceability" between secondary reference materials and primary standards such as Standard Reference Materials produced by NIST.