Age, sex, and racial influences on the Beckman Coulter AccuTnI+3 99th percentile.

BACKGROUND: Beckman Coulter recently released a new cardiac troponin I (cTnI) assay, AccuTnI+3, for the Access 2 and DxI platforms. We validated the stated 99th percentile (20 ng/l) using a large population of healthy adults representative of the Northern California population. METHODS: Within a large sample of healthy adult members receiving care at Kaiser Permanente, cTnI was quantified in residual specimens using the AccuTnI+3 assay. Patients were selected based on pre-defined criteria extracted from a comprehensive electronic medical record. All specimens with a cTnI concentration >30ng/l were repeated; specimens that had a reproducible result >30 ng/l were subject to heterophile blocking procedure. 99th percentiles were calculated based on age, sex, race and body mass index categories. RESULTS: Among 1764 tested subjects, the 99th percentile for all samples was 25 ng/l. Sex differences were observed; the male and female 99th percentiles were 31 and 21 ng/l, respectively (p=0.001). Age (range evaluated 18-89y, median 47y) also had a significant influence on the value (p=0.003), but there were no significant differences by race. False positive results were detected in 0.9% of specimens (0.6% "fliers" and 0.3% heterophile antibodies), corresponding to 52% of all results >30 ng/l. CONCLUSIONS: Among a large, representative cohort of healthy adults, we found a 99th percentile value consistent with prior studies based on highly selected small patient samples. Sex and age-specific upper reference limits for cTnI should be considered. In this cohort, about half the findings above the 99th percentile were false positives. Avoiding reporting erroneous results requires implementation of quality indicators.

Analytical sensitivity of four commonly used hCG point of care devices.

BACKGROUND: Point of care (POC) hCG assays are often used to rule-out pregnancy and therefore diagnostic sensitivity, especially at low concentrations of hCG, is important. There are very few studies in the literature that seek to verify the claimed analytical sensitivity of hCG POC devices. METHODS: The analytical sensitivity of four commonly used hCG POC devices (Alere hCG Combo Cassette, ICON 20 hCG, OSOM hCG Combo Test, and Sure-Vue Serum/Urine hCG-STAT) was challenged using urine samples (n=50) selected based on quantitative hCG concentrations. The majority of these specimens (n=40) had an hCG concentration between 20 and 200 U/L. Each specimen/device combination was reviewed by three individuals. Statistical calculations were performed using Stata 12. RESULTS: The analytical sensitivity of the OSOM was significantly lower inferior than that of the other POC devices. There was no significant difference in the sensitivity of the Alere, ICON 20 and Sure-Vue devices. There was no significant difference in the individual interpretation of the hCG POC results. CONCLUSIONS: All hCG POC devices evaluated in this study were susceptible to false negative results at low concentrations of urine hCG. Laboratorians and clinicians should be aware that there are limitations when using urine hCG POC devices to rule out early pregnancy.

Performance characteristics of the Beckman Coulter total ßhCG (5th IS) assay.

BACKGROUND: Beckman Coulter recently released the first commercially available hCG reagent calibrated against the 5th International Standard (IS) for hCG (total ßhCG (5th IS)). We performed a comprehensive analytical validation of this reagent. METHODS: Precision experiments were completed using 3 concentrations of commercial quality control material. Linearity, sample stability, and analytical sensitivity were evaluated using pools of human serum. Reportable range was assessed by comparing manual dilutions to those performed by the instrument. Male and female reference intervals were established using residual serum specimens submitted for routine testing. Inter-lot variability of hCG assay reagent was assessed by analyzing serum specimens with detectable hCG using 2 different reagent lots. Inter-assay variability was established using 203 serum specimens analyzed for hCG on 6 different reagent platforms. RESULTS: Inter-day precision showed a CV of <6.0% for all concentrations of QC material. LOB, LOD, and LOQ were determined to be 0.3, 0.4, and 0.6 U/l, respectively. The Access (5th IS) reagent has an average positive bias of approximately 20% when compared to most platforms and the previous generation Beckman hCG assay. Results were consistent between lots. Female reference intervals varied by age: <1.0 U/l (<41 y), <6.0 U/l (41-50 y), and <8.0 U/l (>50 y). Male reference intervals were <2.0 U/l. CONCLUSIONS: The analytical performance of the total ßhCG (5th IS) was established. Care should be taken to re-baseline patients needing serial monitoring and/or notify physicians when transitioning to the total ßhCG (5th IS) reagent.

Limitations in qualitative point of care hCG tests for detecting early pregnancy.

BACKGROUND: Detection of early pregnancy in the healthcare setting is important for proper patient management. Qualitative point-of-care (POC) human chorionic gonadotropin (hCG) testing is often used. There is a gap in the literature for evaluating patient samples with low (<300 IU/l) hCG concentration using POC devices. METHODS: Specimens (urine, n=289; serum, n=269) with hCG concentrations between 2 and >5000 IU/l were evaluated by hCG POC testing. Approximately half of these had an hCG concentration<300 IU/l. All specimens were evaluated using the OSOM and QuickVue+ POC hCG devices. Pregnancy status was evaluated by patient chart review. RESULTS: The OSOM and QuickVue+ devices were able to detect hCG in 53% (OSOM) and 78% (QuickVue+) of urine samples with an hCG concentration range between 20 and 300 IU/l. Serum samples with an hCG concentration range between 10 and 300 IU/l gave positive results in 79 and 91% of samples tested using the OSOM and QuickVue+, respectively. False negative results could not be attributed to the high-dose hook effect, the hCG variant effect, or the interpreters' evaluation. The mean gestational age for specimens corresponding to the false negative results was 4 weeks. CONCLUSIONS: The sensitivity of 2 commonly used hCG POC devices is insufficient for detecting very early pregnancy.