Tools, Technologies and Training for Healthcare Laboratories
  2. Home
  3. Essays
  4. Quality Requirements and Standards
  5. Why Not Evidence-Based Method Specifications?

Quality Requirements and Standards

Why Not Evidence-Based Method Specifications?

In the March 2002 issue of Clin Chem, the NACB published a long paper about the use of laboratory tests for patients with diabetes. Dr. Westgard examines their "evidence-based" recommendations, and finds some poor Sigma values. (Preview)

 

 

An updated version of this essay appears on the Nothing but the Truth about Quality book.
March 2002

In March 2002, the Clinical Chemistry journal published a 36 page report by the National Academy of Clinical Biochemistry (NACB) on the use of laboratory tests in patients with diabetes [1]. That is probably the longest paper ever published by Clinical Chemistry, which attests to the importance being placed on "evidence-based laboratory medicine and test utilization" today. The March 2002 issue of Clinical Laboratory News also leads with the headline "NACB Issues Guidelines for Lab Testing in Diabetes" and announces an upcoming interactive audioconference on "The New Diabetes Testing Guidelines: Effects on the Laboratory and Clinical Management."

Why so much attention to diabetes and lab tests? Healthcare for diabetes patients is big business, estimated at $98 billion ten years ago! Laboratory tests are critical for managing the treatment of diabetic patients, so this provides a good opportunity to demonstrate the value of laboratory tests. In today's anti-laboratory regulatory and reimbursement environment, the objective management and treatment of one of today's major diseases (and one of the highest long-term costs in healthcare) depends on laboratory tests.

Evidence-based clinical practice recommendations

The NACB report provides evidence-based recommendations for the use of glucose (including glucose meters for patient use), the oral glucose tolerance test, urinary glucose, ketones, glycated hemoglobin, genetic markers, and microalbuminuria. Glycated hemoglobin emerges as the test with the strongest evidence for use in the evaluation of glycemic control, assessment of risk, establishment of treatment goals, and long-term management of diabetic patients. The report also provides recommendations for the performance specifications of laboratory methods.

The purpose of evidence-based medicine is to demonstrate and document best medical practice on the basis of published studies and expert consensus. The "level of evidence" is graded on a scale from A to E, with A representing the highest level of evidence and E the lowest. The levels are described as follows [1]:

A. "Clear evidence from well-conducted, generalizable, randomized controlled trials that are adequately powered…"
B. "Supportive evidence from well-conducted cohort studies…"
C. Supportive evidence from poorly controlled or uncontrolled studies…:
D. [not yet defined]
E. "Expert consensus of clinical experience."

In this context, the evidence used to establish specifications for the precision, accuracy, and QC of laboratory tests appears to be "expert groups", which is the lowest level in the evidence grading system. It would seem appropriate to consider additional scientific approaches to strengthen the recommendations for method performance specifications. I'll illustrate my concerns for the Glycated Hemoglobin test that is discussed in this report.

Guidelines for Glycated Hemoglobin (GHb)

  • Here's a summary of recommendations from the report [1]:
  • GHb should be measured at least twice a year.
  • Treatment goals should be based on clinical studies such as the Diabetes Control and Complications Trial (DCCT).
  • The desired GHb concentration is 7% or less.
  • Treatment should be reevaluated when GHb exceeds 8%.
  • US laboratories should use methods certified by the National Glycohemoglobin Standardization Program.
  • Methods should have an interassay CV <5% (ideally 3%).
  • Two control materials with different mean values (high and low) should be analyzed at the beginning and end of each day's run.

Nothing but the Truth bookWe invite you to read the rest of this article

This complete article and many more essays are available in the Nothing but the Truth about Quality manual. You can also download the Table of Contents and additional chapters here.