Q

I am a pathologist in a commercial laboratory. Our lab recently started receiving blood specimens on ice from out-of-state physicians’ offices. By the time specimens arrive they can be 30 to 40 hours old. Physicians have started complaining about too many abnormal results, which on our review included marginally increased MCV, high MCHC, and low MC, among others. When the same patient blood was analyzed in a local commercial laboratory, all these marginally abnormal specimens were resulted as normal. Also, our in-state specimens which were analyzed the same day did not have any problems. Although the majority of these results were not clinically abnormal, when the patient sees the abnormal asterisk next to that result it causes anxiety, forcing the physician in charge to draw another specimen and send it to a local lab. Do you have any suggestions that can help us resolve this issue?

A

The complete blood cell count is one of the basic panels used by physicians both to screen for conditions and to monitor treatments for their patients. Therefore it is readily available in most laboratories. The reference ranges are based on the results obtained with fresh specimens. The growing practice of shipping specimens long distances to core laboratories has caused concern about the stability of the parameters and the accuracy of the reported results.¹

There have been a number of studies to determine what changes are seen under varying storage conditions. The majority of these studies have shown that there are definite changes seen as specimens age. Some of the parameters can be stabilized somewhat by refrigeration. ² However, even under controlled refrigeration temperatures there will be significant changes in the MCV and the WBC differential results.¹ It is recommended that all differentials on specimens older than 24 hours be confirmed by a manual slide review from a slide that is prepared within the first eight hours. (Labs should require slides to be submitted with the specimens that are going to be delayed in transit.)

Stability problems will also vary depending on the instrumentation.³ Each manufacturer will have recommendations for stability, and these should be factored into the laboratory’s specimen rejection criteria. In general, the studies reviewed all started seeing changes after 24 hours with refrigerated specimens and as early as four hours with room temperature specimens depending on the type of instrumentation. Review of a number of specimen collection guidelines, found on laboratory websites, provided rejection criteria ranging from 24 hours up to seven days. (The majority were 24 hours.)

If a laboratory is routinely running specimens that are more than 24 hours old, staff should make sure that they are using methodology that is compatible with these older specimens. It would also be advisable to perform an in-house stability study to confirm these stability claims. And finally, for those parameters that might be affected on aged specimens, there should be some kind of notation provided with the results that explains the stability issues and how to interpret those results. This will give the clinicians some additional information in making the decision to have the testing repeated.

References

Turhan T, Sezar S, Yucel C, Koca C. “Effects of storage conditions on complete blood cell count parameters.”Turkish J Biochem. 2011;(36.2):165-174.
Wood BL, Andrews J, Miller S, Sabath DE. “Refrigerated storage improves the stability of the complete blood cell count and automated differential.” Am J Clin Path. 1999;(112.5) 687-695.
Fatime I, Herkoltz R, Risch L, et al. “Stability of hematological analytes depends on the hematology analyser used: A stability study with Bayer Advia 120, Beckman Coulter LH 750 and Sysmex XE 2100.” Clin Chimi Acta. 2008;397 (1-2):68-71.

Q

What are the reference intervals for insulin two hours post 75g of oral glucose? Are they the same for insulin 2hpp?

A

The reference range for the oral glucose tolerance test with a 75-gram dose of glucose is <140 mg/dl of glucose and <10 units of insulin as recommended by the American Diabetes Association (ADA) as well as a number of other sources. The range for the two-hour post-prandial is a bit more controversial, as the ADA reports the glucose target as <180 mg/dl, and most other sources, such as the University of Michigan, have recommended a more conservative value of <140 mg/dl for glucose and <10 units for insulin.

Insulin levels are not routinely performed as part of the tolerance testing at the present time. However, some sources recommend that once the diabetes diagnosis is established, further insulin studies should be performed to determine if the patient has insulin resistance. The results can be helpful in determining a treatment regimen.

References

American Diabetes Association. http://www.diabetes.org/. Accessed April 1, 2014.
Medline Plus: US National library of medicine. Glucose tolerance test. http://www.nlm.nih.gov/medlineplus/ency/article/003466.htm. Accessed April 1, 2014.
University of Michigan Health System. 2-hour postprandial blood glucose test. http://www.uofmhealth.org/health-library/stt11619. Accessed April 1, 2014.