TORCH Test Positive: Introduction, Principle, Test Procedure, Result Interpretation and Uses

ToRCH test

TORCH Test

TORCH test stands for Toxoplasma gondii, other, rubella (German measles), cytomegalovirus, and herpes simplex. Other contains other viruses HIV, Hepatitis viruses, varicella, parvovirus. These all are viruses except Toxoplasma (parasite) and those may be etiological agents of infections in pregnant women which may pass on to a fetus during pregnancy. Therefore, a ToRCH screen, a panel of tests are necessary for early detection and treatment of infections to prevent complications in newborns. These diseases can cross the placenta and cause birth defects in newborns and those conditions are-

  • deafness
  • cataract
  • intellectual disability
  • heart problems
  • seizure
  • jaundice
  • low platelet count
  • To save from these conditions, the doctor suggests the pregnant woman (her first prenatal visit) for TORCH  testing.

The TORCH screen test is of two types

  1. one for immunoglobulin G(IgG) for past infection
  2. and another for  immunoglobulin M(IgM): for an acute infection

Note:  Above picture is showing the ToRCH screen test for immunoglobulin M (IgM) for

  • Toxoplasma gondii
  • Rubella
  • Cytomegalovirus and
  • Herpes  simplex type 1 and 2

All tests are negative except rubella which is positive.

The acronym TORCH was introduced in 1971 to highlight a group of diseases that affect the fetus and newborn, namely Toxoplasma gondii, rubella virus, cytomegalovirus, and herpes simplex virus. The disease often leads to similar clinical features which include one or more of the following clinical signs-

  • low birth weight
  • Prematurity
  • Purpura
  • Jaundice
  • Anemia
  • Microcephaly
  • Hydrocephaly
  • Cerebral calcification
  • Chorioretinitis
  • Cataracts
  • Microphthalmia
  • Hearing
  • Impairment
  • Mental retardness
  • Autism and
  • Pneumonitis

The  TORCH Panel Rapid Test is a lateral flow chromatographic immunoassay for the qualitative detection and differentiation of antibodies (IgG and IgM) to Toxoplasma gondii , rubella virus, cytomegalovirus (CMV), herpes simplex virus 1 (HSV-1), and herpes simplex virus 2 (HSV-2) in human serum or plasma.

Principle of TORCH test

It works on the principle of immunochromatography. Both TORCH IgM and IgG screening tests are Gold Immuno-Chromatography Assay (GICA), based on the sandwich immunoassay principle. Recombinant antigens of all pathogens( one parasite and remaining viruses) and anti-human IgM and IgG antibodies to the parasite and viruses are respectively used to detect the specific antibodies in human serum, plasma, or even in the blood. When the sample is added to the sample pad wells on the test panel, the antibodies, if present in the sample, will react with the anti-human IgM antibody in the membrane strip, and immunocomplex will emerge. These complexes move along the membrane strip chromatographically to the test region (T), where the immunocomplexes will be captured by the pre-coated recombinant antigen. The red or pink line will appear, indicating a positive result for the specific antibody to the microorganisms(parasites and viruses). The unbound complex moves on to the control region (C), where they are captured anti-mouse antibodies, and a red line will appear, indicating the test is valid. In this way, the control line provides internal quality control. The color intensity is in accordance with the related TORCH pathogens in the sample.

TORCH Test Requirements

  • Individually sealed foil pouches containing:
    One cassette device
    Two desiccants
    Plastic droppers
    Sample diluent (Optional according to manufacturers)
    One package insert (instruction for use)
  • Extra we need
  • Gloves
  • Waste bin
  • Specimens: Common serum or plasma even whole blood adjustable in some manufacturer kit-CtkBiotech  ( according to condition, urine, Cerebral spinal fluid may also be used.)
  • Timer
  • Centrifuge

Test Procedure of TORCH Test

  1. Wear gloves.
  2. Allow the test device, specimen ( if stored), or control or diluent to room temperature ( 15-30°C) prior to testing.
  3. Bring the pouch to room temperature before opening it. Remove the test device from the sealed pouch and use it as soon as possible.  Note: Best results will be obtained if the assay is performed within an hour.
  4. Place the test device on a clean and level surface. Hold the dropper vertically and 1 full drop of serum or plasma ( approximately 10 µl ) and two drops of buffer ( approximately 80 µl ) to each specimen well of the test device respectively.
  5. Avoid trapping air bubbles in the specimen well.
  6. Start the timer.
  7.  Wail for the colored line/s to appear.
  8. The results should be read at 15 minutes. Do not interpret the results after 20 minutes.

Result Interpretation of TORCH Test

  • Red or pink line/s only at control region/s: Test Negative
  • Red or pink lines both regions ( at control and test): Test Positive
  • No line or band at all or line/s at test region/s: Test Invalid and thus repeat the test with a new test device
  • Result: Rubella IgM test: Positive
  • Note: The same condition is applicable to the TORCH IgG test panel too.

Keynotes

  • Test negative indicates no infection.
  • IgM test positive indicates current infection.
  • IgM and IgG positive are indicators of recent infection.
  • IgG Positive determines past/chronic infection
  • Rubella can be prevented by vaccination. IgG titer above 15 IU/mL in blood indicates protective immunity.
  • HSV-1 in babies can cause low birth weight, miscarriage, and preterm birth.
  •  Toxoplasma gondii enters the body through the mouth and is at high risk to the fetus when infected during or just before pregnancy. Symptoms, which occur later in life, can include vision loss, mental retardation, deafness, and seizures.
  • Cytomegalovirus (CMV) is a high risk of congenital infection when newly infected during the first half of pregnancy, usually in the first trimester.  CMV can result in hearing loss, epilepsy, and intellectual disability in a developing fetus.
  • HSV-2 is the most common herpes infection in newborn babies. In addition,
    HSV-2 infection increases the risk of contracting HIV.
  • Other tests available for this panel are ELISA and PCR.

Uses of TORCH test

  1. TORCH screening aims to control the transmission of TORCH pathogens and assist doctors in initiating proper action, in particular to pregnant women, as severe fetal damage and other serious complications can occur to newborns.
  2. TORCH panel test is designed for pregnant women and women who are planning to become pregnant.
  3. Before Pregnancy:
    Planning vaccination for rubella
    Proper arrangement of pet care
    Safe sexual conduct
  4. During pregnancy: 
    Eliminating pathogen exposure
    Close monitoring of pregnancy
    Close monitoring of fetal development
    Proper delivery and neonatal strategy

Limitation

  1. This reagent is designed for the qualitative screening test. Concentration cannot be determined by this qualitative test.
  2. The results of the reagent are only for clinical reference, which is not the only basis for clinical diagnosis and treatment. A confirmed diagnosis and treatment should only be made by a physician, after all, clinical and laboratory findings have been evaluated.
  3.  A negative result may occur when detecting short-term infected samples,
    indicate that the specific antibodies that do not exist or the concentration is below the detection limit. If TORCH infection is still suspected, the sample should be collected 1-2 weeks later and carry the parallel detection with the first sample.

Precaution

  • The instructions must be followed to obtain accurate results. Anyone performing an assay with this product must be trained in its use and laboratory procedures.
  •  Wear protective gloves while handling specimens. Wash hands thoroughly afterward.
  •  The sample must be fresh for the test, avoiding freezing repeatedly.
  • The test result is invalid over 20 minutes.
  • Do not use after the expiration.
  •  If the patient, for the first time, is infected in less than 5 days, with no
    detected specific antibody, the result will be negative when testing.
  • Do not use other kinds of quality control samples to test the reagent.
    Components of different batches cannot be exchanged for use to avoid
    the erroneous result
  • For in vitro diagnostic use only. Do not re-use test device
  • Do not eat or smoke while handling specimens.
  • Avoid splashing or aerosol formation
  • Clean up spills thoroughly using an appropriate disinfectant
  • Decontaminate and dispose of all specimens, reaction kits, and potentially contaminated materials, as if they were an infectious waste, in a biohazard container.
  •  Do not mix with other specimens.

Bibliography

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5924842/
  2. https://www.invitro-test.com/IVD-reagents/immuno-assay/eugenics/TORCH-Test-Kits.php
  3. https://ctkbiotech.com/product/torch-panel-rapid
  4. http://www.rapidtest.com/index.php?product=TORCH-Panel
  5. https://www.btnx.com/Product?id=1970
  6. http://www.athenesedx.com/marketing/torch.pdf
  7. http://www.spectrum-diagnostics.com/new/pdf/09_Rapid_Test/ToRCH.pdf
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