How collection works
Dec 23, 2025
How does the collection work
Every item in the Rythm at-home collection kit has been carefully curated to support the pre-analytical phase of testing, ensuring that a simple at-home process produces laboratory-quality biomarker data and capillary samples that match the analytical performance of traditional venous draws. If you are just looking for collection instructions, see our video here.
Warming the site: the sodium acetate phase-change heat pack
Before collection, you warm the upper arm using a reusable click-to-heat pack. Warming increases superficial blood flow through local vasodilation, creating more reliable capillary filling and reducing hemolysis. It also improves comfort for kit users.
Chemically, these packs operate on a reversible phase transition. Inside the sealed pouch is a supersaturated solution of sodium acetate trihydrate. When the internal metal disc is flexed, microscopic shock waves and surface disruptions create nucleation sites, triggering rapid crystallization.
This crystallization process is exothermic. As the sodium acetate trihydrate lattice forms, latent heat is released and the temperature stabilizes near 50-58 degrees Celsius (122-136 degrees Fahrenheit). Because this is a physical phase change rather than a consumptive chemical reaction, the pack can be reset repeatedly by boiling until all crystals dissolve. Once cooled undisturbed, the supersaturated liquid reforms and can be activated again.
For collection purposes, the heat pack enhances microcirculation, increases total capillary volume available to the device, improves filling efficiency of the Tasso+ system, and improves user comfort.
Preparing the skin: the alcohol wipe
The isopropyl alcohol wipe reduces microbial load on the skin, removes oils and topical residues, and improves adhesion of the Tasso device. Adhesion quality directly influences the integrity of the negative-pressure seal, which is required for efficient vacuum-assisted capillary filling.
The alcohol must be allowed to dry fully. This prevents stinging, avoids dilution of the first microvolume of blood, and enhances adhesive performance. Effective skin preparation also reduces the likelihood of sample contamination.
Collecting the blood: the Tasso+ device
The Tasso+ is the primary collection instrument in the Rythm Health kit. It is an FDA-cleared Class II medical device under the 510(k) pathway and is categorized as a single-use blood lancet with integrated sharps-injury-prevention features.¹ This regulatory status requires substantial equivalence testing, mechanical and safety validation, and compliance with device quality system regulations.
Mechanistically, the device functions through a controlled sequence.
The warmed and cleaned upper arm is prepared, and the device is adhered firmly using a medical-grade adhesive. This adhesive ring creates a closed environment necessary for consistent vacuum action.
When the activation button is pressed, a sterile lancet performs a rapid dermal puncture and retracts immediately into a protected chamber. Negative pressure is generated within the device and draws capillary blood into the attached microtube.
Capillary flow continues until the tube reaches the intended volume or the recommended collection time has elapsed. The device is removed, the filled tube is detached and capped, and the sample is prepared for transport.
This design yields higher sample volumes than traditional fingerstick methods. Because pressure is not applied manually, dilution with interstitial fluid is minimized. The collection process also reduces hemolysis and produces analytically consistent samples. Studies report low pain scores and high user acceptability in both adults and children using this platform.² ³ ⁴ ⁵
Lithium heparin microtube
Rythm Health uses lithium heparin microtubes for biochemical assays. Lithium heparin inhibits coagulation by neutralizing thrombin and related enzymes without strong chelation of calcium or magnesium, preserving biochemical fidelity across a wide range of analytes.
Lithium heparin plasma is suitable for metabolic panels, liver function testing, hormone assays compatible with plasma, and high-throughput proteomic workflows. Studies of Tasso-collected capillary plasma demonstrate strong agreement with venous lithium heparin or serum specimens across multiple assay categories.⁴ ⁶
Gauze and bandage
Upon removal of the device, gauze is applied briefly to support hemostasis by facilitating platelet plug formation. A bandage protects the puncture site from friction, sweat, and environmental exposure, ensuring rapid and uncomplicated healing.
Protecting the sample: the 3D-printed travel tube
After collection, the microtube is placed in a rigid 3D-printed travel container. While microcollection tubes are robust in clinical settings, they are not engineered for the mechanical stresses encountered during automated mail transport.
The travel tube acts as a rigid exoskeleton, protecting against compression, torsion, microfractures, and cap displacement. It preserves sample integrity, anticoagulant ratios, and orientation, helping prevent pre-analytical variability.
Scientific validation: equivalence of capillary and venous samples
A growing body of peer-reviewed literature demonstrates that Tasso-collected capillary blood yields results comparable to venous draws across a wide range of analytes.⁴ ⁶
A recent systematic review and meta-analysis comparing self-collected capillary blood with venous sampling found that laboratory results were largely concordant and pain perception was generally lower with capillary self-collection.⁷
SARS-CoV-2 immunology (serology)
In paired-sample studies using Tasso-SST devices, capillary and venous samples showed high quantitative and qualitative concordance for anti-SARS-CoV-2 IgG antibodies measured by ELISA.⁸
A large independent cohort study using unsupervised home collection reported a 93 to 94 percent success rate and excellent agreement, with a Deming regression slope near 1.00, between capillary and venous IgG measurements under both standard and stress-simulated shipping conditions.⁴
High-throughput proteomics
In a pilot study using the Olink inflammation panel, capillary samples collected with Tasso+ and matched venous samples demonstrated acceptable correlation for a subset of proteins when processed within 24 hours. Longer delays increased variability, highlighting the importance of timely processing for certain proteomic applications.⁹
Therapeutic drug monitoring and chemistry
Published studies show that Tasso-collected capillary blood performs comparably to venous samples for general chemistry, liver enzymes, serologic testing, and selected proteomic assays.⁹ ¹⁰ Peer-reviewed pharmacokinetic validation specific to therapeutic drug monitoring remains limited, but available evidence supports equivalence for many routine clinical assays.
Together, these data show that with appropriate tubes, validated assays, and controlled pre-analytical handling, capillary self-collection using Tasso devices can produce results closely equivalent to traditional venous sampling.
Bringing it together
You warm the upper arm to increase blood flow and comfort.
You clean and dry the skin to optimize adhesion and reduce contamination.
You activate the Tasso+ device to perform a controlled dermal puncture and vacuum-assisted collection.
You cap and protect the microtube in a rigid travel container for shipment.
You apply gauze and a bandage to support healing.
The sample is then processed on laboratory analyzers validated for lithium heparin plasma, using assays shown in published studies to perform comparably to venous draws.
The result is a carefully engineered at-home collection system that preserves pre-analytical integrity and produces laboratory-grade data.
References
FDA. 510(k) Premarket Notification for Single-Use Blood Lancet With an Integral Sharps Injury Prevention Feature (K221131). 2022.
Dasari H, Smyrnova A, Leng J, Ducharme FM. Feasibility, acceptability, and safety of a novel device for self-collecting capillary blood samples. PLoS ONE. 2024;19(5):e0304155.
Schröder D, Behrens E, et al. Pain and feasibility of capillary self-blood collection using the Tasso+ upper-arm device. Primary Health Care Research & Development. 2025.
Hendelman T, Chaudhary A, LeClair AC, et al. Self-collection of capillary blood using Tasso-SST devices for anti-SARS-CoV-2 IgG testing. PLoS ONE. 2021;16(9):e0255841.
Schmetzer C, Vogt E, Stellar L, et al. Self-collection of capillary blood and saliva for COVID-19 vaccine immunogenicity. Frontiers in Public Health. 2022;10:994770.
Applied Clinical Trials Online. At-home self-collection of blood specimens for safety lab testing via the Tasso+ device. 2023.
Comparison of laboratory results and pain perception in self-sampled capillary versus venous blood: a systematic review and meta-analysis. Clinical Biochemistry. 2025;138:110965.
Hendelman T, Chaudhary A, LeClair AC, et al. Comparison of capillary blood self-collection with venous phlebotomy for SARS-CoV-2 antibody measurement. Journal of Immunological Methods. 2023;520:113523.
El-Sabawi B, Huang S, Tanriverdi K, et al. Capillary blood self-collection for high-throughput proteomics. Proteomics. 2024;24(3–4):e2300607.
Maselli DJ, Hendelman T, et al. Standard venipuncture versus capillary blood collection for the prospective determination of abnormal liver chemistry. Journal of Applied Laboratory Medicine. 2023;8(3):535–550.