GENITAL SPECIMENS AND THE NEW MDS METRO REQUISITION

Since the release of the new MDS Metro requisitions we have noted an increase in the number of specimens that arrive labelled Vagina but have the Vaginal-Anal box checked off on the requisition instead of the Vaginal box. This creates confusion as to what testing to perform and requires the laboratory staff to call the ordering physician's office to clarify the site so appropriate testing can be performed.

Vaginal swabs are routinely processed to include a gram stain, bacterial vaginosis grading and gonorrhea culture. Group B streptococcus culture will be performed on a vaginal specimen if specifically requested, however, the recommended specimen for prenatal group B strep screening is a vaginal-anal swab. A vaginal-anal swab is only cultured for group B streptococcus. It is not appropriate to test for bacterial vaginosis, yeast or Trichomonas from a vaginal-anal swab. The vaginal-anal box on the requisition should only be checked off if the swab is specifically for prenatal group B streptococcal screening only.

Therefore, it is very important for the physician's office to check off the correct box on the requisition (vaginal-anal vs. vaginal) and to have the swab labelled with the correct site (vaginal-anal vs. vaginal). This will prevent numerous calls from the laboratory to the physician's office and also ensure that proper testing is done for the patient.

NEW MDS METRO POLICY FOR REJECTING LOW QUALITY SPUTUM SPECIMENS

Diagnosis of the etiology of bacterial lower respiratory tract infections using sputum culture is often complicated by the contamination of specimens with upper respiratory tract secretions (saliva) during collection. Because the upper respiratory tract may be colonized with potential bacterial pathogens not involved in infection of the lower respiratory tract, the laboratory staff must ensure that an appropriate specimen is processed. It has become increasingly evident in the diagnostic microbiology literature that sputum specimens determined by microscopic screening to be poor quality (highly contaminated with saliva) and with little evidence of inflammation (WBCs) should not be processed for bacterial culture. It can be very misleading to report culture results from such specimens.

Therefore, at MDS Metro we will no longer process such low quality sputum specimens for bacterial culture. We will aim to perform microscopic screening of sputum specimens submitted for bacterial culture on the day of arrival so a report can be sent to the physician the following day if the sputum is found to be unacceptable for bacterial culture, allowing the physician to contact the patient to collect another specimen without delay if clinically indicated. The report for a sputum rejected for bacterial culture will have the comment "Sputum screening indicates excessive oropharyngeal contamination, therefore bacterial culture not performed. Please repeat specimen if clinically indicated." We will not bill for culture of rejected sputum specimens.

Important exceptions to note:

1. Sputum specimens identified on the requisition as belonging to immunocompromised, neutropenic or transplant patients, or those sputum specimens that are visibly bloody, will have bacterial culture performed regardless of the results of microscopic screening.
   
2. Sputum screening and rejection criteria are reserved for Bacterial culture requests only. In the case of sputum requests for suspected mycobacterial, fungal or viral illness, microscopic screening is not relevant, and all sputum specimens will be processed for these organisms when requested.

NEW PROTEIN ELECTROPHORESIS SERVICE

In the near future, protein electrophoresis testing will be consolidated in our Burnaby Reference Laboratory. A new, more sensitive procedure will be used to replace the two current methodologies in use. This change will be reflected in slightly different reference ranges and protein quantitation. For monoclonal proteins being followed on an ongoing basis, the change may cause a small bias from previous results. Assistance in interpretation of results, especially where previously stable gammopathies appear changed, may be obtained by calling either:

Dr. David Aitken (604) 412-4412 or

Dr. Margaret Kelly (604) 412-4426.

The change in methodology will be noted on the report form when this takes place.

HOMOCYSTEINE REFERENCE RANGES

Elevated homocysteine (Hcy) appears to be an independent, graded risk factor for atherosclerotic and thromboembolic disease: however, appropriate reference ranges are still under investigation.

Laboratory reference limits are often derived from the central 95% of results obtained for an apparently healthy population. This model may be inappropriate for Hcy if the unknown incidence of coronary heart disease (CHD) risk or inadequate vitamin status is high in the reference population. The significance of higher values in males and older adults also needs to be clarified. Similar issues were resolved for cholesterol about ten years ago, when values well below the statistical reference range were shown to confer a higher-than-baseline risk for premature CHD.

Several investigators have used vitamin supplementation to define reference ranges for plasma Hcy. In one study, the reference range estimate (central 95%) for vitamin replete men aged 18 to 65 years was 4.9 to 11.7 m mol/L. 1 In another study, the population that had little change in Hcy following folate supplementation (presumably initially vitamin replete) had these pre-supplement results (central 95%):2

 

Subgroup	Hcy (m mol/L)	h
<30y Males/Females	4.6 - 8.1	30
30-59y Females Males	4.5 - 7.9 6.3 - 11.2	45 43
>60y Males/Females	5.8 - 11.9	51
All	4.9 - 11.4	169

In the European Concerted Action Project, a large case-control study to examine Hcy associated vascular risk, elevated fasting plasma Hcy was defined as a result in the top quintile (20%) of a control population, >12 m mol/L.3 Gender and age trends 4 were similar to those of the supplementation study sited above:

European Concerted Action Project

 

Subgroup	Hcy (m mol/L): 80th percentile limit	h
<45y Females Males	10.4 11.9	135 232
45-60 Females Males	11.4 12.6	95 338
All	12.1	800

Differences in both methodology and specimen handling are affecting results at this time. Until more epidemiological data is available and standardization occurs, reference ranges will continue to be adjusted as consensus is reached. Also note, as stated in the St. Paul’s Hospital Laboratory Medicine Bulletin, that "there have been no completed prospective, double blind, placebo controlled trials that demonstrate that reduction of homocysteine levels with vitamin treatment reduces morbidity and mortality". The Bulletin further recommends the restriction of Hcy measurement to:

1. individuals with severe premature atherosclerosis or repeated deep vein thrombosis or pulmonary emboli when there are few other risk factors present or
2. those with severe family history for CAD, but no usual risk factors in affected family members or
3. those with clinical features consistent with homocystinuria or
4. those with possible latent vitamin B12 deficient dementia.
   

References:

1. Ubbink JB, Becker PJ, Vermaak WJH, Delport R. "Results of
   B-Vitamin Supplementation Study Used in a Prediction Model to Define a Reference Range for Plasma Homocysteine." Clinical Chemistry 41 (7) 1995, 1033-37
   
2. Rasmussen K, Moller J, Lyngbak M, Pedersen AH, Dybkjaer L. "Age- and Gender-Specific Reference Intervals for Total Homocysteine and Methylmalonic Acid in Plasma Before and After Vitamin Supplementation." Clinical Chemistry 42 (4) 1996, 630-36.
   
3. The European Concerted Action Project. "Plasma Homocysteine as a Risk Factor for Vascular Disease." Journal of the American Medical Association 277 (22) 1997, 1775-81.
   
4. Refsum H, Ueland PM, Nygard O, Vollset SE. "Homocysteine and Cardiovascular Disease." Annual Review of Medicine 1998, 31-62.
   
5. Urquhart N and Frohlich J. "Change in Total Homocysteine Method." St. Paul’s Hospital Laboratory Medicine Bulletin, Oct. 27, 1998