A-225 Validation of self-collected capillary dried plasma spot collection for lipoprotein(a) testing
Authors: Naranjo A , Muldrow R , Carter C , Chen J , Beal S 
Published: October 2024

Abstract

Background
Cardiovascular disease is prominent among socially disadvantaged populations that do not have the resources for standard health screening. Self-collected capillary Advance Dx (ADX) dried plasma spot cards could address these issues by offering access to clinically acceptable lipid screening from remote collections. Our laboratory currently uses ADX specimens to screen for cholesterol, calculated LDL, HDL, glucose, lipoprotein (a) (LP(a)), and triglycerides, however, the current study will focus on the validation of self-collected capillary ADX specimens for LP(a) testing.

Methods
ADX LP(a) was measured using the Tina-quant Lipoprotein (a) Gen.2 assay on the Roche cobas c702 closed development channel. All closed development channel assay parameters followed the standard assay, except sample volume increased from 2 to 18uL. Calibration was performed using Roche LP(a) calibrators diluted 1:10 with water. Patient specimens were prepared by collecting four 6mm punches from the plasma portion of the ADX card. Samples were resuspended in 400uL of 0.1% bovine serum albumin and incubated for 30 minutes at room temperature (RT) while shaking at 250 RPM. Non-biological materials were diluted 1:13 with water to match the sample-to-diluent ratio of the extracted patient ADX specimens. A correction factor (CF) was derived and challenged using total protein (TP) as an internal standard. BioRad Lipids Control (BRLC) and ADX patient specimens were run for wet and dry matrices to establish imprecision. Accuracy was determined using BRLC and ADX patient specimens. Linearity was confirmed by running 5 levels of Maine Standards Linearity Cardiac CM3 Kit. ADX stability was observed at RT and under summer/winter conditions to account for shipping to the laboratory.

Results
Specimens tested between venous and ADX LP(a) to derive the CF (n=70) had a bias of 21.92 mg/dL (132.28%) and a linear equation of (y=2.40x -1.23; R=0.985). Average card TP was 4.36 g/dL. The resulting CF is: reported ADX LP(a) = ((4.36/card TP)*card LP(a)*2.397)-1.23. Matched venous and ADX specimens that challenged the CF (n=50) had a bias of -1.00 mg/dL (-3.33%) and a linear equation of (y=0.98x -0.25; R=0.994) at the medical decision point of 30.00 mg/dL. Imprecision was 2.4% and 2.4% for BRLC specimens with mean concentrations of 15.04 and 29.40 mg/dL, respectively. Imprecision was 4.2% and 10.5% for ADX patient control specimens with mean venous target concentrations of 66.85 and 14.81 mg/dL, respectively. BRLC had an average bias of -0.31 mg/dL (-2.03%) and 0.41 mg/dL (1.40%) for levels 1 and 2, respectively. ADX patient specimens (n=3) had average biases of -1.47 mg/dL (-3.83%), 1.43 mg/dL (2.15%), and -1.58 mg/dL (-10.64%). ADX LP(a) concentrations from 6.0-80.0 mg/dL were linear (y=1.04x -0.45; R=0.999). The ADX specimen is stable for at least 7 days at RT and at least 5 days under summer and winter shipping conditions.

Conclusions
All assay parameters met acceptability criteria and were less than the total allowable error of 28.8%. Self-collected capillary ADX specimens are acceptable for the clinical measurement of LP(a), and effectively improve access to testing and identifying high-risk individuals as therapeutic strategies for treatment of elevated LP(a) continue to emerge.