Physicians' Newsletter Volume 13, Issue 3
Tuesday, 26 April 2011 00:00
In this issue
- Semen analysis changes
- Laboratory monitoring of dabigitran etexilate (PradaxTM) therapy
- Better recovery of yeast by culture at BC Biomedical
- Download PDF of issue
Semen analysis changes
Effective April 26, 2011, BC Biomedical will adopt the recently revised reference values for semen parameters published by
the World Health Organization (WHO).1
The new reference limits are derived from analysis of semen quality and fertility data obtained from men whose partner conceived within 12 months after stopping use of contraception.2 WHO has elected to use the 5th centile rather than the more usual 2.5th centile for the lower limits of the reference range.
New Semen Reference Ranges
| Semen volume | >1.4 mL |
| pH | >7.1 |
| Sperm concentration | >14 X 106/mL |
| Total sperm number per ejaculate | >38 X 106 |
| Sperm motility - total | >39% |
| Sperm motility - forward | >31% |
| Sperm viability (live sperm) | >57% |
| Normal sperm morphology | >3% |
Please note:
- Men whose semen characteristics fall below the lower limits given here are not necessarily infertile; their semen characteristics are below the reference range for recent fathers — as are, by definition, those of 5% of the fertile men who provided data used in the calculation of the reference range
- A man’s semen characteristics must be interpreted in conjunction with clinical information
- It is impossible to characterize a man’s semen quality from evaluation of a single semen sample
We are also pleased to announce successful implementation of a Computer Assisted Sperm Analysis (CASA) instrument (IVOS) for the routine reporting of sperm count, motility, viability and morphology. The IVOS hardware and software have been specifically designed to produce objective and consistent results to enhance quality reporting of sperm parameters. Of particular note is the ability of IVOS to evaluate sperm morphology using the strict criteria developed by Dr. T.F. Kruger, which is the morphology classification system recommended by WHO. The IVOS software program for morphology assessment has been validated by Dr. Kruger. In-house validation studies conducted by BC Biomedical indicate that the IVOS morphology software results closely match manual morphology assessments. As noted in the accompanying table, the new reference range for normal sperm morphology will be >3%.
For more information, please contact any member of the Hematopathology Group at 604-507-5000.
References
- World Health Organization Department of Reproductive Health and Research. WHO laboratory manual for the examination and processing of human semen, 5th edition, WHO Press, Geneva, Switzerland 2010.Cooper, T.G., et al. World Health Organization reference values for human semen characteristics. Hum Reprod Update 2010; 16(3): 231-45
Laboratory monitoring of dabigitran etexilate (Pradax™) therapyResults
Dabigitran etexilate (Pradax™) is a new oral direct thrombin inhibitor which is approved in Canada for the prevention of thromboembolic complications associated with total hip/total knee replacement or with atrial fibrillation. Unlike warfarin, its predictable pharmacokinetic profile allows for a fixed-dose regimen without the need for routine laboratory monitoring.
However, in certain clinical situations (e.g. serious hemorrhage, potential overdose, emergency surgery etc.), it may be necessary to make a laboratory assessment of a patient’s anticoagulation status prior to making management decisions. In general, this will usually only be required in a hospital setting (e.g. emergency room) and is unlikely to be required for outpatients who are receiving the drug.
We are aware that some outpatients receiving dabigitran are being referred to BC Biomedical for INR and/or aPTT tests. As dabigitran acts on thrombin-mediated conversion of fibrinogen to fibrin, it has an effect on all routine coagulation assays including the INR and aPTT but neither test is entirely satisfactory in that:
INR
- Dabigitran has little effect on the INR at clinically relevant plasma concentrations
- The INR is only about 2.0 even with supra-therapeutic doses of dabigitran
aPTT
- The aPTT will increase with dabigitran therapy but the dose response curve flattens at higher concentrations of the drug and the aPTT is relatively insensitive within the range of plasma concentrations seen in patients
It would appear that a modification of the thrombin time is likely going to be the test of choice to assess the presence or absence of anticoagulant effect1 although this test is not yet standardized across BC laboratories. In addition, therapeutic levels based on a modified thrombin time have not yet been established. As noted above, patients who might require assessment of their anticoagulation status are most likely being seen within a hospital setting therefore, at present, BC Biomedical has no plans to offer the modified thrombin time.
Practice points:
- Routine laboratory monitoring of dabigitran (Pradax™) therapy is NOT usually necessary
- A prolonged aPTT will reflect the presence of dabigitran in the patient’s plasma but is relatively insensitive
- In the absence of availability of a modified thrombin time, the aPTT can be used but only to assess the presence/absence of the drug
- If a modified thrombin time is required because of bleeding, emergency surgery or invasive procedure etc., please refer patient to a hospital laboratory for testing
Please direct any questions/concerns to any member of the Hematopathology Group at 604 507-5000.
References
-
van Ryn J et al Dabigitran etexilate—a novel, reversible, oral direct thrombin inhibitor: Interpretation of coagulation assays and reversal of anticoagulant activity. Thromb and Haemostasis 2010;103:1116-1127
Better recovery of yeast by culture at BC Biomedical
The Genital Specimen guidelines that laboratories in BC follow have recommended investigation for yeast by reading a Gram stain slide. BC Biomedical has performed multiple studies and found that the diagnosis of candidiasis was enhanced if performed by culture rather than just by Gram stain but this is more costly and time-consuming. More than half of the vaginal specimens with significant growth of Candida were falsely-negative by Gram stain alone. The Gram stain can usually be prepared and read within 24 hours whereas yeast culture takes two days.
In the interest of delivering high quality results, we will continue to perform Gram stains plus yeast cultures on vaginal specimens even though we are only remunerated by the Medical Services Plan for the Gram stain portion of the exam. So, please be aware that “Vaginitis initial presentation” results will usually take two days.
Please direct any questions/concerns to any member of the Microbiology Group at 604-507-5000.
