SOP-S-005 — Serum Qualitative Beta-hCG Pregnancy Test SOP

1.0 Purpose

This procedure covers the qualitative detection of human chorionic gonadotropin (β-hCG) in human serum at Tarangnan Community Hospital using the Abbott Bioline hCG rapid immunoassay, including procedural control checks and clinical limitations.

2.0 Scope

This procedure applies to all qualitative serum pregnancy testing by Medical Technologists in the Clinical Laboratory for emergency, outpatient, inpatient, and pre-operative services. It covers specimen preparation, cassette loading, internal control validation, and diagnostic interpretation for early gestation, suspected ectopic pregnancy, and trophoblastic disease. General serological operations are governed by Serology Section Workflow Quality Control and Result Reporting Sop.

3.0 Definitions

• Human Chorionic Gonadotropin (hCG): Glycoprotein hormone secreted by syncytiotrophoblasts of the developing placenta shortly after blastocyst implantation.
• Beta-Subunit (β-hCG): Structurally unique polypeptide chain of the hCG dimer conferring immunological specificity and preventing cross-reactivity with LH, FSH, and TSH.
• Analytical Sensitivity: The lowest analyte concentration reliably producing a positive test result (25 mIU/mL for Abbott Bioline hCG).
• Hook Effect (High-Dose Hook): False-negative or deceptively faint test line caused by extremely high antigen concentrations that saturate both capture and conjugate antibodies simultaneously.
• Ectopic Pregnancy: Extrauterine implantation of a fertilized ovum, typically associated with subnormal, atypical, or slowly rising β-hCG titers.

4.0 Responsibility

4.1 Hospital Director

• Approves this procedure and ensures authorized pregnancy test kits and cold-chain storage are available.

4.2 Pathologist

• Provides clinical and technical oversight, advises on discordant or unexpected findings, and correlates results with ultrasound evidence.

4.3 Chief Medical Technologist / Laboratory Quality Manager

• Maintains version control of this procedure, verifies reagent lot performance, and oversees staff competency.

4.4 Medical Technologists

• Verify specimen suitability (clear serum without gross hemolysis).
• Follow the exact 3-drop / 100 µL loading volume, time strictly with a digital timer, and read results at 3 minutes.
• Validate the procedural C line on every test cassette and enforce the 10-minute maximum reading cutoff.

4.5 Laboratory Aides

• Clean analytical surfaces, record daily refrigerator temperatures, and maintain clean inventory.
• Shall not perform testing, dispense serum, interpret test lines, or release laboratory findings.

5.0 Policy / Procedure

5.1 Clinical Application and Analytical Principle

• Analytical Principle: Abbott Bioline hCG is a rapid, one-step lateral-flow chromatographic immunoassay for the qualitative detection of β-hCG in serum. The test cassette contains a membrane pre-coated with anti-hCG capture antibodies on the test line region (T) and goat anti-mouse IgG on the control line region (C). As the serum sample migrates, it rehydrates colloidal gold-conjugated monoclonal anti-β-hCG antibodies. When hCG is present at ≥ 25 mIU/mL, an immune complex is captured at the test band, forming a distinct pink-to-red line.
• Clinical Utility: diagnostic confirmation of pregnancy, investigation of acute pelvic or lower abdominal pain in women of reproductive age, pre-operative screening, emergency medication clearance, and radiological safety clearance.

5.2 Reagent Kit and Storage Requirements

• Kit specifications: Abbott Bioline hCG (Cat. No. 30FK10, 25 tests/kit), analytical sensitivity 25 mIU/mL.
• Storage and stability: - Store sealed foil pouches between 1 °C and 30 °C (34–86 °F). Do not freeze. - Stable until the stamped expiration date on the pouch when stored properly. - Do not use test cassettes beyond the printed expiration date.
• Inspect individual pouches before opening. Discard any pouch that is torn, punctured, or unsealed. Open the pouch immediately before testing.

5.3 Specimen Requirements and Thermal Equilibration

• Specimen collection requirements: - Collect venous blood into a plain red-top tube or gold-top serum separator tube (SST). - Allow complete spontaneous clotting for 30–60 minutes at room temperature. - Centrifuge specimen at 1,000–1,200 × g for 10 minutes to obtain clear serum.
• Verify specimen quality: - Test only clear, non-hemolyzed serum. Grossly hemolyzed, icteric, or lipemic specimens shall be rejected per Phlebotomy Workflow Unacceptable Specimens and Adverse Reactions Sop. - Do not use specimens showing visible microbial contamination or precipitate.
• Thermal equilibration: if serum has been stored refrigerated at 2–8 °C, allow both the serum tube and test cassette pouch to equilibrate to ambient room temperature (15–30 °C) for 15–30 minutes before initiating testing.

5.4 Analytical Bench Procedure

• Cassette setup: remove the test cassette from the sealed pouch and place it on a clean, dry, horizontal bench surface. Label the cassette with the patient laboratory accession number.
• Specimen loading: - Draw clear serum into the provided disposable plastic dropper. - Hold the dropper vertically directly above the round sample well (S). - Dispense exactly 3 free-falling drops (approximately 100 µL) of serum into the sample well (S). Ensure no air bubbles are trapped in the well. - Do not add chase buffer or diluent (serum is tested neat).
• Start a dedicated digital bench timer immediately upon dispensing the third drop.
• Reading window and critical cutoff: - Read and interpret results at exactly 3 minutes. - Critical reading cutoff: do not interpret results after 10 minutes. As the nitrocellulose membrane dries, background evaporation and reagent precipitation can generate faint non-specific lines, causing false-positive interpretations.

5.5 Result Interpretation

• Positive (Reactive): - Two distinct pink-to-red colored bands appear: one in the control line region (C) and one in the test line region (T). - Any visible intensity of the T line, even faint, indicates a positive result (≥ 25 mIU/mL).
• Negative (Non-Reactive): - Only one pink-to-red colored band appears in the control line region (C). - No colored band appears in the test line region (T). - Indicates that β-hCG is absent or below the 25 mIU/mL detection threshold.
• Invalid Result: - No colored band appears in the control line region (C), regardless of whether a line appears in the test line region (T). - Indicates insufficient specimen volume, improper technique, or degraded reagent. Retest immediately using a new cassette from a fresh pouch.

5.6 Quality Control and Verification

• Internal procedural control: the appearance of a distinct colored line at the control region (C) serves as an internal positive procedural control. It verifies that adequate sample volume (100 µL) was applied and proper capillary wicking occurred across the nitrocellulose strip.
• External QC testing: test commercial positive and negative control materials upon receiving each new kit shipment, each new reagent lot, and whenever unexpected results occur. Document QC findings in the Serology QC Logbook before releasing patient results.

5.7 Clinical Limitations and Diagnostic Considerations

• Early gestation: very early in pregnancy (such as days before an expected menstrual period), serum β-hCG levels may be below 25 mIU/mL, yielding a negative result. If pregnancy is clinically suspected, advise retesting with a new specimen in 48–72 hours.
• High-dose hook effect: in rare cases of extremely elevated β-hCG (such as gestational trophoblastic disease, hydatidiform mole, or choriocarcinoma where hCG exceeds 500,000 mIU/mL), antigen excess may cause a false-negative or paradoxically faint test band. If molar pregnancy is suspected, dilute the serum 1:10 or 1:100 with normal saline and repeat testing.
• Ectopic pregnancy: ectopic gestations frequently present with abnormally low or plateaued β-hCG levels. A negative or faint qualitative result does not rule out an ectopic pregnancy; urgent clinical evaluation and pelvic ultrasound are essential.
• Post-partum or post-abortion persistence: detectable levels of β-hCG may linger for several days to weeks following delivery, spontaneous miscarriage, or therapeutic termination.
• Non-pregnant elevated hCG: certain non-gestational conditions, including germ cell tumors, ovarian cysts, and heterophile antibodies, can cause elevated hCG in the absence of viable intrauterine pregnancy.

5.8 Result Reporting and Clinical Communication

• Standardized reporting terminology: - "Negative for Serum β-hCG (Pregnancy Test)" - "Positive for Serum β-hCG (Pregnancy Test)"
• Standard report disclaimer: "Qualitative immunoassay with an analytical detection sensitivity of 25 mIU/mL. A negative result in very early gestation does not exclude pregnancy. Test results must be correlated clinically with ultrasound and clinical history."
• Urgent clinical notification: for emergency room patients presenting with acute pelvic pain, suspected ruptured ectopic pregnancy, or trauma, report positive results verbally to the attending emergency physician immediately after verification, and record the verbal notification in the LIS.

6.0 Records

7.0 References

• DOH Clinical Laboratory QMS Tool, Section 3 — Service Delivery
• DOH Administrative Order No. 2021-0037, Annex B1 — Technical Standards for Clinical Laboratories
• ISO 15189:2022, Section 7.3 — Examination Processes

Companion policies:

• Serology Section Workflow Quality Control and Result Reporting Sop — Serology section general workflow, QC, and result reporting
• Laboratory Reporting Policy — Result reporting, validation, and clinical communication
• Laboratory Retention Schedule Policy — Master retention schedule for serological records and requisitions