Case-control diagnostic accuracy study with 130 potential pediatric PID+ (primary immunodeficiency) patients, and 100 age-matched, healthy controls (PID-). The potential PID+ participants will be recruited prospectively through 9 hospitals in Sindh and Punjab states or contacted via the PID surveillance registry developed by AKU Hospital's Polio Excretion in PID study to identify children with primary antibody deficiency (PAD+: a type of PID+); healthy, age-matched PID-participants will be recruited by snowball sampling. At the point of care, health care workers (HCWs) will collect capillary blood samples (0.1mL) to run the PID rapid screening test and reader on potential PID+ participants (identified by exhibiting >2 of the Jeffrey Modell warning signs) and healthy, age-matched controls. All pediatric study participants will be sent to the hospital lab to have a confirmatory immunology panel (see 4.4.1 Diagnosing PID for the battery of tests) run on a serum/plasma sample to confirm their PID diagnosis (PID+/PAD-, PID+/PAD+, PID-); a 1.5uL aliquot of serum/plasma will simultaneously be used to run a PID rapid screening test by a laboratory technician (LT). HCWs and LTs will be blinded to true PID status. Blood and serum PID rapid screening test results will be compared to the confirmatory immunology panel to determine diagnostic accuracy. All clinical management of study participants will follow the standard of care for PID in Pakistan and will be based upon the immunology panel result. The HCWs and LTs administering the tests will be trained prior to the diagnostic accuracy test (see Objectives below) and will provide feedback on the tool post-training and post-use to assess usability, acceptability, and feasibility of integrating the test and digital reader into tertiary hospitals for the purpose of improved national PID surveillance, improved PID patient care, and polio eradication in Pakistan.

Inclusion Criteria:

• Aged 3 months to 15 years

  • Presents for care at 1 of 9tertiary hospitals participating in the study
  • Potential PID+ (Case): Child is identified by HCW to have >2 Jeffrey Model warning signs of PID. [Note: Upon immunology panel testing, this group will be separated into three categories: PID-, PID+, and PID+/PAD+ meaning they have 1 of 5 relevant primary antibody deficiencies (PAD+)].
  • PID-(Control): Child is identified (by snowball sampling) as being in good health, and having the same age (within 12 months) as another child who produced a PID+ result.
  • Caregiver consents to participate in the study and provides informed consent. If their children are 10 years of age or older, that child must also give assent.

Exclusion Criteria:

• Aged less than 3 months or greater than 15 years of age

  • Caregiver does not consent to participate, or child >10years does not give assent to participate.
  • Having received IVIG in the past 90 days

- 130 potential PID patients with (5 relevant PIDs: PADs) within Sindh and Punjab states V1.0, 6 Jan 2022

• 100 healthy, age-matched children within Sindh and Punjab state

The data generated by this study will inform decisions regarding product development and commercialization of the BioSure PID rapid screening test and digital reader. The data collected in this evaluation may be used to support regulatory approval of the test. The study will generate valuable data on the performance of this novel test in comparison to that of the Jeffrey Modell warning signs and the immunology panel enabling informed decision-making regarding recommendation of new highly sensitive POC tools for PID. Data will be shared with study partners and the test developers. This may include de-identified, individual-level data.