Details create the big picture.

In clinical chemistry, the evolution of how data is utilized by caregivers continues to require laboratories to respond with increasing layers of detailed information. As more health insurers and government agencies seek measurement of the quality of patient care, the laboratory is poised to provide that data, often from information it already has.

eGFR as adjunct / replacement

Adoption of the calculated glomerular filtration rate (also known as electronic glomerular filtration rate, or eGFR) as an adjunct to or replacement for the 24-hour urine creatinine clearance test has not been without its problems. Using the serum creatinine, gender, age, and race, it is possible to calculate the glomerular filtration rate--the basis of the traditional creatinine clearance test--but without the usual problems associated with 24-hour urine collection. The impetus to performing this calculation stems from the National Kidney Disease Education Program, whose primary goal is to improve the early detection and treatment of kidney disease. Many labs continue to struggle with the mechanics of providing this calculation to their physicians. Issues encompass:

* which calculation to use (Modification of Diet in Renal Disease, or MDRD, or Cockcroft-Gault);

* whether or not the laboratory information system can support the calculation; and

* whether or not to calculate the eGFR on all creatinine tests performed by the laboratory or specifically by request.

Many instrument and reagent vendors have adopted the isotope-dilution mass-spectrometry (IDMS) standardization for their creatinine methods, although this method is still not universal. The difference in creatinine values between IDMS and non-IDMS methods, along with normal ranges, makes eGFR testing an ongoing situation that requires good communication between the laboratory and caregivers who utilize creatinine test results.

The EAG calculation debate

Estimated average glucose (EAG) is another calculation based on existing clinical-chemistry data that is receiving increased attention from healthcare providers as well as insurers. One of the challenges in diabetes care is helping the patient better understand the relationship between his daily glucose levels as measured by self-monitored blood-glucose testing versus a quarterly or semiannual hemoglobin Alc measurement performed by the laboratory. The EAG calculation can provide a clear interpretation of a patient's glycemic status--essentially comparing "apples to apples." The results of the Alc derived average glucose (ADAG) study demonstrated a linear relationship between Alc levels and average glucose levels in both type 1 and type 2 diabetics. A previous calculation derived from the Diabetes Control and Complication Trial was based on a much more limited study than the ADAG, and values from this calculation are higher than the EAG values. While the American Diabetes Association and the American Association for Clinical Chemistry both have endorsed the use of the calculation, ongoing debate and additional studies of the EAG calculation continue.

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Vitamin D

There is probably not a clinical-chemistry laboratory in the country that has not experienced a marked increase in the number of requests for vitamin D testing. Low vitamin D status has long been associated with osteopenia, osteoporosis, and fracture risk. Meta-analysis has provided some intriguing possibilities, associating low vitamin D levels to increased risk of certain cancers, type I diabetes, heart disease, multiple sclerosis, Alzheimer's disease, and overall mortality. While these studies are far from definitive at this point, the popular press has taken kernels of information and helped spur the demand for vitamin D testing. But what can be termed a low vitamin D level? Unlike glucose or sodium, where population studies can define a true normal range, vitamin D levels have many variables that must be considered to determine a normal range. Because of the effect of sunlight on 7-dehydrocholesterol in the skin, vitamin D levels are affected by such variables as season, geographic location, population ethnicity, and gender. Establishment of a meaningful normal range would have to include these variables. Our immediate knowledge of vitamin D metabolism and what should be considered "healthy" levels is also based on dietary intake recommendations that are more than 50 years old.

Currently, the Institute of Medicine is conducting a study to determine updated dietary-intake levels for vitamin D. It is expected that the existing adult recommended daily intake of 200 IUs to 400 IUs will be adjusted based on more up-to-date scientific data. Finally, laboratories need to be aware of the lack of method standardization for vitamin D testing at this time. Different methods will yield different results, which can lead to confusion if a physician utilizes different laboratories for vitamin D testing and tries to compare the two values. The National Institute of Standards and Technology is now working on providing standardized reference material for quality control and calibration of vitamin D testing. As with eGFR and EAG, ongoing communication between the laboratory and physicians regarding the ins and outs of vitamin D testing will be essential in providing meaningful details to create the big picture of patient care.

By Debbi Tiffany, MSEd, MT(ASCP) SC, SLS

Debbi Tiffany, MSEd, MT(ASCP) SC, SLS, is the director of Laboratory Services at SwedishAmerican Health System, Rockford, IL.