Editor’s note: This month, Anthony Kurec, MS, H(ASCP)DLM, returns as our clinical expert, answering questions from three readers. Anthony is Clinical Associate Professor, Emeritus, at SUNY Upstate Medical University in Syracuse, NY.
Q The reference lab we use wants some 24-hour urine specimens with acid preservatives in the collection containers. The only ones currently requested are 50% acetic acid and 6N HCl. Our concerns are about sending these home with outpatients. I know we have done so in the past, and put warning labels on the containers, but now we are having second thoughts. There are also liability issues, especially in this litigious atmosphere. Do you have any suggestions?
A Most 24-hour urines can be adequately preserved by refrigeration; however, for some analyses a chemical additive is needed. Determinations for urinary calcium, steroids, and vanillylmandelic acid (VMA) are best preserved with an acid pH of 3 or less, while testing for porphyrins, urobilinogen, and uric acid requires an alkaline environment.1
If the procedure requires chemical preservation, then there is little recourse unless the analysis on the 24-hour urine can be completed shortly after collection. Many laboratories are not equipped to handle this and subsequently must send it to a reference laboratory for analysis.
Potentially hazardous chemicals in the hands of a non-laboratorian could be a problem and the litigious issue raised is a concern. Use of warning labels on the containers is critical, in addition to discussing the potential dangers with the patient.2 Documentation of the patient instruction (require patient and witness signatures) of the potential chemical hazards would add another level of safety. Review this with legal counsel to ensure wording of any document is appropriate.
If the reference laboratory has a local draw site, you could refer the patient there, thus removing your laboratory from the concerns raised. Another option is to send them to another nearby laboratory that can perform the requested test(s).
References
- Young DS, Bermes EW, Haverstick DM. Specimen collection and other preanalytical variables. In: Burtis CA, Ashwood ER, Bruns DE, eds. Tietz Fundamentals of Clinical Chemistry. 6th ed. 2008:42-62.
- Sanford KW, McPherson RA. Preanalysis. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. 2011:24-36.
Q For CSF cell counts when the WBC count is normal (≤5) for an adult, is it necessary or useful to perform a differential? Also, for other body fluids such as pleural or peritoneal fluid, if a low WBC count is obtained, such as <50, is it necessary or useful to perform a differential?
A The normal range for CSF cell counts is 0-5 cells/µL in adults and 0-30 cells/µL in neonates. CSF cell counts are often performed manually by chamber, which can have a coefficient of variation (CV) as high as 45-48% due to the low number of cells present.1 Generally, inadequate specimen volume and/or cell numbers usually preclude the use of automated methods. The most reliable method for differentials is to cytocentrifuge 0.5 mL of specimen with a small amount of albumin, thus preserving the cellular morphology.
It has been shown that leukemic CSF specimens can have a normal cell count but have blast cells present.2,3 Cell counts on non-malignant CSF specimens (viral/bacterial infections, degenerative disorders, or other inflammatory diseases), generally exceed the upper reference range (>5 cells/µL); thus differentials on cell counts less than this would most likely offer limited clinical information. Including this in the protocol is a clinical decision and should be made by the appropriate personnel.
Examination of other body fluids (synovial, pleural, pericardial, peritoneal) is most often performed when a patient shows signs of inflammation or infection with an accumulation of that fluid type. Because of greater fluid volume, more cells are generally present but can vary in number from just a few to thousands. On those specimens with a low cell count (<50 cells/µL), first ensure that it is not clotted, which would make the count inaccurate.4 CAP recommends cytocentrifuging preparations even with low cell counts. Body fluids can contain a variety of cell types, including non-hematopoietic cells (mesothelial, synoviocytes, histocytes, etc.) or rare malignant cells.The final determination of when to perform differentials, especially on CSF specimens, must be approved by the medical director and made part of the laboratory protocol.
References
- Karcher DS, McPherson RA. Cerebrospinal. Synovial, serous body fluids, and alternative specimens. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. 2011:480-506.
- Maroeska D, Loo WM, Kamps A, et al. Prognostic significance of blasts in the cerebral spinal fluid without pleiocytosis or a traumatic lumbar puncture in children with acute lymphoblastic leukemia: experience of the Dutch Childhood Oncology Group. J Clin Oncolog. 2006;24(15):2332-2336.
- Burger B, Zimmerman M, Mann G, et al. Diagnostic cerebrospinal fluid examination in children with acute lymphoblastic leukemia: significance of low leukocyte counts with blasts or traumatic lumbar puncture. J Clin Oncolog. 2003;21(2):184-188.
- Galagan KA. Q&A. CAP Today. 2012;26(1):80.
