Pediatric Critical Care Fellow Medical College of Wisconsin
Children's Wisconsin Medical College of Wisconsin Milwaukee, Wisconsin, United States
Background: Flow Cytometry (FC) is used often to aid in the diagnosis of primary immune deficiencies (PID). Currently, a major obstacle in the field is efficient testing for PID in varying clinical settings. These tests are sent in varying states of patient health and clinical settings, and it is unknown how this affects test results.
Objective: We sought to determine if clinical status affects the likelihood of obtaining abnormal FC results. We hypothesized that patients in the ICU are more likely to have abnormal tests making their results less useful for clinical management.
Design/Methods: We retrospectively analyzed FC results and included any subject with two or more FC tests. Each test measured the absolute counts of up to 4 lymphocyte subsets: CD3+CD4+, CD3+CD8+, CD19+, and/or CD56+16+. Results were designated a percentage of those measurements that were normal (%normal). We then identified which clinical division ordered the test and the final diagnosis. A generalized linear mixed model with Maximum Likelihood Estimation was used to compare the tests ordered by clinical areas after considering the repeated tests within patients. Statistical significance was set at p<0.05.
Results: Of a total of 6,462 tests from 1,515 patients, 11% of all tests had measurements which were 100% normal, and only 42 patients (2.7% of total patients) had every test with 100% normal measurements. Of the 1,370 patients who had their first test with <100% normal measurements (an abnormal intial test), 224 patients had testing that “normalized” in future testing. When the mean %normal measurements were ranked by the 8 clinical divisions (after excluding tests from the bone marrow transplant, oncology, solid organ transplant, and HIV divisions), tests ordered by the Allergy division had the highest %normal measurements and tests ordered in the ICU had the lowest %normal measurements. The difference for both was statistically significant when compared with other clinical divisions (Table 1). Conclusion(s): These results confirm that FC can be greatly affected by the clinical status of the patient, as supported by the high rate of abnormal tests in the ICU, while outpatient testing had higher rates of normal tests. These data suggest that FC testing to identify PID during critical illness may result in a high false positive rate, and that this testing should be delayed until the clinical status of the patient has improved. Further work is ongoing to identify which patients were subsequently diagnosed with PID in varying clinical settings.
Table 1. Percent normal measurements for each ordering clinical area ranked from highest mean %normal to lowest mean %normal.
Authors/Institutions: Ali Hemyari, Medical College of Wisconsin, Milwaukee, Wisconsin, United States; Liyun Zhang, Medical College of Wisconsin, Milwaukee, Wisconsin, United States; Jenny Andres, Children's Wisconsin, Milwaukee, Wisconsin, United States; John Routes, Medical College of Wisconsin, Milwaukee, Wisconsin, United States; Ke Yan, Medical College of Wisconsin, Milwaukee, Wisconsin, United States; James Verbsky, Medical College of Wisconsin, Milwaukee, Wisconsin, United States
