Flow cytometry in cerebrospinal fluid—Rational use of laboratory services
Authors: Eric D. Hsi
Journal: American Journal of Hematology (2014)

Flow cytometric analysis (FCA) of cerebrospinal fluid (CSF) is commonly used to assess whether there is central nervous system involvement by hematologic malignancy (HM). Several studies have been published over the years extolling its use, finding varying numbers of cases in which morphologic assessment was negative but FCA identified the presence of leukemia or lymphoma cells 1-6. The results of such studies and the conclusions drawn depend greatly on the methods employed, such as the type of stain used for morphologic review and the training and experience of the observers. For example, the use of Papanicolaou and DiffQuick stains, which are typically used in cytologic preparations, may not provide optimal nuclear and cytologic details brought out by a high quality Wright–Giemsa stain in lymphoma and leukemia cells. Ideally, morphologic assessment should be performed by experienced laboratory-based hematopathologists/hematologists. In the current health care environment, laboratories are pressed to add value to the care of patients by providing quality laboratory testing at reduced cost. Part of this endeavor includes optimizing test utilization. In this issue of the American Journal of Hematology, Kovach et al. examined the diagnostic utility of FCA of CSF in patients both with and without histories of prior HM 7. Of 255 samples, 137 (54%) were from patients with prior HM while 118 (46%) were from patients with neurological abnormalities. In this cohort 18 were abnormal by FCA, 17 of which were derived from patients with HM. Six of the 16 with cytologic evaluation (Papanicolaou and DiffQuick) were abnormal. While 3 of the 10 cases with negative cytology were chronic lymphocytic leukemia (CLL), the remaining 7 had negative cytology, underscoring the need to perform FCA in all cases with the history of HM. Conversely, two samples from patients with a history of HM were morphology positive but FCA negative. Thus, in keeping with other studies, the combination of the two modalities is complementary. With regard to the patients with neurologic abnormalities only (no history of HM), only 1 case (out of 118 samples from 108 patients, less than 1%) was positive by flow cytometry. In this sample, a surface immunogloblin negative B-cell population was detected without clear morphologic evidence of a malignancy. This flow cytometry finding is abnormal but likely, in this clinical context, insufficient for definitive diagnosis. However, it did prompt further investigation and in this patient a diffuse large B-cell lymphoma was subsequently diagnosed by brain biopsy. One other patient from this group had abnormal morphology but normal FCA and this patient was diagnosed with diffuse large B-cell lymphoma (DLBL) after further investigation. Thus, even in this group the two modalities can be complementary. The rate of FCA positivity is, of course, markedly different between patients with and without HM. Statistically, the authors show much higher positive rates in the patient group with history of HM. Indeed it can be seen that, as a group, FCA added little to the care of patients without a history of HM. What features might be used then to define a subgroup for which FCA would be of higher yield? From their data set, the only feature Kovach et al. identified was cell count 7. Since the one patient with negative morphology but positive by FCA did indeed have an elevated white blood cell count (WBC) (>5/μL), the authors conclude that this would be reasonable criterion on which to base the decision to perform FCA. This would have resulted in 23% fewer flow cytometry studies, a significant savings and a policy supported by evidence. Limiting FCA in CSF to those with history of HM or, in the absence of this history an elevated WBC would be a practical policy for the study authors, given their workflow. But why stop there? In a similar study design, we reviewed our laboratories experience in which air-dried Wright–Giemsa stained smears are evaluated by a hematopathologist prior to the decision to perform FCA 8. All FCA positive cases were seen when patients had at least one of two features: (1) history of HM, or (2) atypical cells consistent or worrisome for HM. In part based on this data, our practice is to contact the ordering clinicians and discourage the performance of FCA when these condition were not met. Only in extenuating circumstances is FCA performed after this contact. As pressure increases to reduce overall costs to the health care system, studies such as these are critical to ensure we are doing the right test at the right time for the right patients. It is too easy to become enamored with application of technology and to become lax in our responsibility as laboratorians to ensure that tests are appropriately utilized. In fact, incentives are now evolving so that utilization of testing is more intensely scrutinized by administration and payors. Kovach et al. are to be commended for generating data that will aid in this cause and increase efficiency for our healthcare system overall.