Physicians' Newsletter Volume 12, Issue 2
Thursday, 16 September 2010
In this issue
- Testing for Diabetes in Pregnancy
- Interpretation of Ferritin Results
- Dietary and Medication Restrictions for Fecal Occult Blood Tests
- The Sting of the Butterfly
- Download PDF of issue
Testing for Diabetes in Pregnancy
The International Association of Diabetes and Pregnancy Study Groups (IADPSG) have issued new recommendations1 for the diagnosis of diabetes mellitus and gestational diabetes in pregnancy. These recommendations are based on the “Hyperglycemia and Adverse Pregnancy Outcome” (HAPO) study.2
Testing for Gestational Diabetes
The IADPSG consensus recommendation is that all women (except those already identifi ed as having overt or gestational diabetes) should be tested at 24-28 weeks gestation for gestational diabetes. The standard test now has collections at 0, 1 and 2 hours after a 75g glucose load, with the patient starting in the fasting state. Diagnostic thresholds are listed in Table 1.
Table 1: Diagnosis of Gestational Diabetes
| Fasting glucose | > 5.1 mmol/L |
| 1 hour glucose | > 10.0 mmol/L |
| >2 hour glucose | > 8.5 mmol/L |
Note: One or more values above the thresholds are considered diagnostic of gestational diabetes.
Many laboratory requisitions currently in use have a check box identifying the older, 3 hour 100g glucose load as the standard test for gestational diabetes. As of October 1, 2010, BC Biomedical Laboratories will perform the newly recommended 2 hour 75g test if this box is checked off.
The IADPSG did not address the use of the 1 hour, 50g screening test. Physicians may choose to bypass the one hour screen and proceed directly to the formal, 2 hour 75g diagnostic test. Note that the new criteria will result in a several-fold increase in the number of patients diagnosed with gestational diabetes (the HAPO study identifi ed 17.8% of an unselected pregnant population as having overt or gestational diabetes), and that the sensitivities and specifi cities of the 50g test with respect to the newer, more liberal criteria have not been published.
Testing for Overt Diabetes Mellitus in Pregnancy
There was debate within the IADSPG as to whether screening in early pregnancy for overt diabetes should be universal, or should be limited to those determined to be at high risk. If a decision to test for overt diabetes is made, it should take place at the first prenatal visit. Tests that may be used and interpretive criteria are listed in Table 2.
Note that if fasting glucose is the preferred test, this will likely require the patient to make an additional trip to the laboratory, and that a random glucose, if elevated, requires confirmatory testing. Measurement of HbA1c does not require either a fasting collection or confi rmatory testing.
Table 2: Testing for Overt Diabetes at First Prenatal Visit (only one of these tests is required)
| Test/Result | Interpretation/Follow-up | |
| Fasting glucose or Random glucose or HbA1c |
≤ 5.0 mmol/L |
No biochemical evidence of overt diabetes. Perform gestational GTT at 24-28 weeks. |
| Fasting glucose | 5.1 – 6.9 mmol/L | Diagnostic of gestational diabetes. Testing for GDM at 24-28 weeks NOT required. |
| Fasting glucose or HbA1c |
≥ 7.0 mmol/L ≥ 6.5% |
Diagnostic of overt diabetes. Testing for GDM at 24-28 weeks NOT required. |
| Random glucose | ≥ 11.1 mmol/L | Consistent with overt diabetes. Confirmation required. |
Note: HbA1c results from BC Biomedical Laboratories are standardized to the same method as used in the Diabetes Control and Complications Trial.
Please direct any questions or concerns to any member of the Medical Biochemistry Group at 604-507-5000.
References
- IADPSG Study Panel. Diabetes Care 2010; 33: 676-682
- The HAPO Study Cooperative Research Group, Hyperglycemia and Adverse Pregnancy Outcomes. NEJM 2008; 358: 1991-2002
Interpretation of Ferritin Results
On June 15, 2010, the joint BCMA/MSP Guidelines and Protocols Advisory Committee issued a revision to the document, “Iron Defi ciency - Investigation and Management” (www.BCGuidelines.ca).
The guideline reaffi rms serum ferritin as the test of choice to diagnose iron deficiency but made the following points:
- Serum ferritin may be unreliable in patients with chronic disease or malignancy
- Non-hematologic symptoms can occur when the serum ferritin is in the low normal range (i.e. less than 50 ug/L in adults)
- Higher levels of serum ferritin do not exclude iron deficiency
- Patients with persistently elevated serum ferritin levels (greater than 1000 ug/L) in the absence of a chronic inflammatory disorder should be tested for iron overload (refer to “Iron Overload – Investigation and Management” at www.BCGuidelines.ca)
In an effort to help physicians assess iron status from the serum ferritin results, BC Biomedical Laboratories will shortly be providing the following guide on our reports:
| Adults (>18 Years of age) | |
| < 15 ug/L | diagnostic of iron deficiency |
| 15 - 49 ug/L | probable iron deficiency |
| 50 – 100 ug/L | possible iron deficiency |
| >100 ug/L | iron deficiency unlikely. If result is persistently >1000 ug/L, consider test for iron overload (transferrin saturation) |
| Children (<19 years of age) | |
| <12 ug/L | diagnostic of iron deficiency |
Please direct any questions or concerns to any member of the Medical Biochemistry or Hematopathology Groups at 604- 507-5000.
Dietary and Medication Restrictions for Fecal Occult Blood Tests
Extensive published trials report that dietary and medication restrictions have no statistically significant effect on the positivity of the guaiac fecal occult blood test.1 Effective immediately, BC Biomedical Laboratories no longer requires patients to modify their diet except for eliminating vitamin C supplements and citrus fruits/juices for 3 days prior to and during collection of samples. This practice has been instituted elsewhere in Ontario and British Columbia. As a “screening” test, we recognize that some results will be falsely positive but the incidence of false positivity does not appear to be related to diet or medication including low-dose salicylate (ASA) or non-steroidal anti-inflammatory drugs (NSAIDS).
We hope these changes will improve our service and have the additional benefit of lessening patient inconvenience. Please direct any questions or concerns to any member of the Medical Biochemistry Group at 604-507-5000.
References
-
Rabeneck L, Zwall D, Goodman JH et al. Cancer Care Ontario guaiac fecal occult blood (FOBT) laboratory standards: evidentiary base and recommendations. Clin Biochem 2008 41(16-17): 1289-305.
The Sting of the Butterfly
We have reviewed the dangers of using various needles and have found that butterfly needles are associated with an 11-fold higher risk of needlestick injuries to our medical laboratory assistants than are regular needles. Butterfly needles comprise only a small minority of the needles we use but are responsible for the vast majority of these injuries. We are all aware of the increasing incidence of HIV and hepatitis as well as the recognition that a variety of other diseases can be spread via blood exposures. At BC Biomedical, we take precautions to minimize the risk of blood exposures to our patients and to our staff. Wherever possible, we use needles with safety devices and plastic specimen tubes.
Due to the higher risk, we have asked our staff to reserve the use of butterfly needles for those patients who truly require a butterfly needle [children who may be uncooperative, patients with venous access limited to delicate hand veins, special tests that require tubing for technical reasons] wherever possible.
We now have regular needles available that are of similar, or even smaller, gauge than the butterfly needles…so size of the needle is no longer an issue. Some of our patients have been told, erroneously, by our staff and by other healthcare workers, that they should ask for butterfly needles on a routine basis. Many of these patients do not require a butterfly. Unfortunately, over recent years, this has led to a significant increase in inappropriate use of butterfly needles with a resulting increase in the risk of blood exposures -
despite the institution of so-called “safety” needles.
So, we want you to be aware of why we are discouraging the use of the butterfly needles, and ask that you help us by being informed of the high risk that these butterflies pose.
Please help us take the sting out of the butterfly!
