Readers Respond

Dec. 1, 2003
Letters to the EditorStatistical vs. clinical significant numbersI read with great interest the Tips from clinical experts Q&A in the April 2003 issue of MLO, page 39, Comparing two analyzers, particularly the answer in testing the null hypothesis. The author states that the traditional cut-off value indicating significance is p<0.001. According to the Michelin Guide scale p<0.05 is significant, p<0.01 is highly significant and p<0.001 is extremely significant. I think that needs to be clarified.Just because something is statistically significant does not mean that it is clinically significant. If the laboratory only used a narrow range of specimens, such as in a normal range study on both instruments, a small difference can make the comparison have a value of p<0.001 but the clinical significance is miniscule. (See McGlasson DL, et al., Rapid removal of platelets from plasma utilizing the Hepcheck heparin removal filter, Blood Coagulation and Fibrinolysis 8, 16-20,
A very well-explained definition of what that value means is the explanation about the probability indicating that the p<0.001, due to chance alone, is less than one in a thousand. Sometimes, laboratorians get caught up in numbers that do not have a clinically significant relevance in relation to their statistical outcome. David L. McGlasson, MS, CLS/NCA
Research Scientist
59th Clinical Research Squadron
Lackland AFB, TX
Multiple views misleadingIn answering the question in the May 2003 MLO issue under Management Q&A on page 42, concerning blood draws without physician orders, an attempt is made to present multiple views from the management panelists. This could be misleading to readers. Only the advice of Ms. Bailey should be heeded. The risk inherent in continuing the practice described far outweighs customer satisfaction in the long run. The practice should be discontinued, with proper communication to all customers, as soon as possible.Donald J. Cannon, PhD
National Manager Special Projects
Quest Diagnostics Inc.
Understated data valueMLOs June 2003 issue, page 44, regarding the usefulness of the oral glucose tolerance test (OGTT) is understated. Mr. Dennis J. Ernst writes that, Formal GTT are no longer generally recommended.While the American Diabetes Association (ADA) does recommend the measurement of fasting plasma glucose (FPG) as the preferred mechanism for testing for diabetes or pre-diabetes, the ADA states:The OGTT may be necessary for the diagnosis of diabetes when the FPG is normal;1The FPG test and the 75-g oral glucose tolerance test (OGTT) are both suitable tests for diabetes,1 andScreening (for pre-diabetes) should be carried out only as part of a healthcare office visit. Either an FPG test or a 2-h OGTT (75-g glucose load) is appropriate … .2There exist extensive data that the OGTT is more sensitive than measuring FPG alone for the diagnosis of diabetes or pre-diabetes.3-5 Based upon this analysis and the ADA position statements, laboratorians should not discourage the use of the 2-point (zero time and +2 h) 75-g oral glucose tolerance test in the diagnosis of diabetes or pre-diabetes if the initial FPG result is not elevated (e.g., <110 mg/dL).William E. Winter, MD
Professor, Pathology, Immunology and Laboratory Medicine, Pediatrics
and Molecular Genetics and Microbiology
Medical Director/Section Chief, Clinical Chemistry
Director, Pathology Residency Training Program
ReferencesAmerican Diabetes Association. Screening for type 2 diabetes. Diabetes Care. 2003. Jan;26 Suppl 1:S21-4.Sherwin RS, Anderson RM, Buse JB, Chin MH, Eddy D, Fradkin J, et al. American Diabetes Association. The prevention or delay of type 2 diabetes. Diabetes Care. 2003. Jan;26 Suppl 1:S62-69.Gomez-Perez FJ, Aguilar-Salinas CA, Lopez-Alvarenga JC, Perez-Jauregui J, Guillen-Pineda LE, Rull JA. Lack of agreement between the World Health Organization category of impaired glucose tolerance and the American Diabetes Association category of impaired fasting glucose. Diabetes Care. 1998. Nov;21(11):1886-1888.Gabir MM, Hanson RL, Dabelea D, Imperatore G, Roumain J, Bennett PH, et al. The 1997 American Diabetes Association and 1999 World Health Organization criteria for hyperglycemia in the diagnosis and prediction of diabetes. Diabetes Care. 2000. Aug;23(8):1108-1112.Gimeno SG, Ferreira SR, Franco LJ, Hirai AT, Matsumura L, Moises RS. Prevalence and 7-year incidence of Type II diabetes mellitus in a Japanese-Brazilian population: an alarming public health problem. Diabetologia. 2002. Dec;45(12):1635-1638.© 2001 Nelson Publishing, Inc. All rights reserved.