Immunochromatography: express diagnostics in the family doctor's bag

Reznikova O.I., Velkov V.V.
CJSC "DEACON"
5 Nauki Ave., Pushchino, Moscow region, 142290
http://www.diakon-diagnostics.ru/Immunochromatographic express diagnostics (ICED) is a new high–tech method that allows not only to accurately diagnose a large range of the most serious pathologies (myocardial infarction, dangerous infections, inflammatory processes, oncological diseases, hormonal disorders, etc.) outside of laboratory conditions and within 5-20 minutes, but also to assess their severity.

The widespread use of ICED makes it possible to detect diseases at an early stage and prevent their development, especially for prostate tumors and complications of diabetes mellitus. Some of these tests are so simple that they can be performed at home.Where the IHED is held.

Where the patient is located. At his house. In the ambulance. In the doctor's office at the initial outpatient appointment, so as not to send the patient to unnecessary, complex and expensive laboratory tests. In general, outside the laboratory, although, of course, it is possible in it. No wonder these tests are called "POCT - POint of Care Testing" in English, which can be translated as "conducting a test at the place of care". In the Russian literature, the term "bedside diagnostics" is sometimes used, which, strictly speaking, narrows the potential of immunochromatographic express diagnostics.Who conducts IHEAD.

Almost anyone. These tests are so simple to perform (unlike laboratory tests) that they can be performed by any more or less trained person. Take a blood or urine sample, put it on a chromatographic plate and after 5-10 minutes get an unambiguous answer: "YES" or "NO". Due to the fact that the answer is unambiguous and the control is always present next to the same plate, there are no problems with interpreting the results. When.

First, when "procrastination is like death." In case of emergency. For example, when there is a suspicion of a heart attack and it is necessary to quickly, reliably, unambiguously and independently of the subjective feelings of the patient to confirm or exclude the development of acute myocardial infarction (AMI) in order to avoid its severe complications due to untimely or improper treatment. After all, none of the common methods guarantees absolutely reliable diagnosis of AMI. Up to 25% of all AMI do not cause any changes on the ECG, and from 20% to 30% of all AMI cases generally occur without a pain attack, especially in the elderly, as well as in patients with diabetes and hypertension. And with the help of ICED, myocardial infarction can be diagnosed right on the spot in 5 to 20 minutes. This can be done with the help of tests with 100% specificity indicating the presence in the blood (in whole, or in serum or plasma) of such cardiac proteins as myoglobin (the earliest marker of AMI), MB isoenzyme creatine kinase (CK MB), troponin I. It is also important that capillary blood can be used as a test sample, which facilitates sampling, or serum, which, unlike heparinized plasma, can also be used for other biochemical studies. The minimum detectable level (cut off), specificity and determination time for AMI markers is:
troponin I – 1 ng/ml, 100%, 15-20 min,
myoglobin – 100 ng/ml, 100%, 10 min,
CK MB – 7 ng/ml, 100%, 15-20 min.Secondly, when there is at least the slightest suspicion of a serious infection, the development of which can be dangerous not only for the patient, but also for others.

Tests unambiguously and quickly detect the pathogen antigen or antibodies produced in response to it. Needless to say, how important it is to quickly determine the presence of: hepatitis B virus antigens, antibodies to hepatitis B and C viruses, HIV 1 and HIV 2, Epstein-Barr virus (infectious mononucleosis) and other, albeit less dangerous, but very common viruses. The sensitivity of the hepatitis B virus antigen test is up to 0.5 ng/ml, the detection time is 20 minutes.

The sensitivity of the test for antibodies to hepatitis B virus is 30mm/ml, the detection time is 10-15 minutes, capillary blood testing is possible. The test is useful for determining the status of a patient before vaccination against hepatitis B. Tests for antibodies to hepatitis C virus and HIV 1,2 have a 100% correlation in sensitivity and specificity with other internationally recognized tests, the determination time is 10-15 minutes. It is possible to use capillary blood.Some tests, such as tests for rotavirus, adenovirus or respiratory syncytial virus (RSV), allow timely detection of the disease in children's groups, maternity hospitals or hospitals and take immediate anti-epidemic measures.

The sensitivity and specificity of the test for adenovirus antigen in faeces 100% coincides with the results of enzyme immunoassay, the determination time is 15 minutes.

The sensitivity and specificity of the rotavirus antigen test in faeces is 100% relative to the FUMOUZE latex test, the determination time is 15 minutes. The sensitivity of the RSV test in nasopharyngial smears relative to the immunofluorescence test is 85.7%, specificity is 91.6%, determination time is 15 min.It is difficult to overestimate the importance of tests for the presence of antibodies and / or antigens indicating syphilis, tuberculosis, chlamydia, streptococci A and B, damage to the gastrointestinal tract by clostridium toxin or the bacterium Helicobacter pylori.

In addition, all these tests can be used as additional methodologically independent confirmatory tests. The sensitivity of the IgG, gA and IdM test to tuberculosis bacillus (350 IU/ml) is selected in such a way that the blood of healthy vaccinated people does not give false positive test results.

The test can be very useful for the diagnosis of non-pulmonary forms of tuberculosis, such as bone tuberculosis, tuberculosis of internal organs and tuberculosis of the genitals. Specificity – 92.8%, determination time – 10-15 min. Capillary blood testing is possible.The sensitivity and specificity of the test for IgG, gA and IdM antibodies to T.pallidum in serum is 100% relative to traditional tests, the determination time is 10-15 minutes.

The test for chlamydial antigen in smears from the cervical canal or urethra has 93% sensitivity and 99.7% specificity compared to PCR diagnostics, the detection time is 20 minutes.

It is possible to use this test not only to detect Chlamydia trachomatis, but also to detect Chlamydia pneumonia in sputum.The streptococcus A test in a pharyngeal smear has 91.8% sensitivity and 97.7% specificity from the culture method.

The determination time is 5-10 minutes. The test can also be used at home.The test for streptococcus in vaginal smears has 88.4% sensitivity and 97.9% specificity from the culture method.

The determination time is 5-10 minutes. The test is useful for detecting infected women in labor.The IgG test for Helicobacter pylori has a sensitivity of 10-15 U/ml and a specificity of 100%.

The determination time is 10-15 minutes. It is possible to use capillary blood..A test for clostridium toxin A in faeces is very useful for detecting antibiotic-related diarrhea.

The identification of the toxin has a clear advantage over the isolation of the pathogen, since not all strains of clostridium are pathogenic. Sensitivity – 86.7%, specificity – 91.7%, detection time – 15 min.When managing patients with diabetes mellitus, one of the main problems is to recognize the occurrence and development of diabetic nephropathy in time, the consequences of which can be the most severe.

Its indicator is albumin in urine in the range of 20-200 mg/ml (microalbuminuria). However, microalbuminuria is also characteristic of patients with persistent hypertension, it also predicts severe pregnancy complications (eclampsia and preeclampsia) and is the most important indicator in post-transplant follow-up of patients with a transplanted kidney. Highly sensitive microalbumin tests (qualitative and semi-quantitative) can be used even by the patient himself at home. A semi-quantitative rapid screening test for albumin in urine has 3 variants of results: up to 10 mg/l, from 10 to 20 mg/l and over 20 mg/l.

The test is active in a wide pH range (2.5-9.5). There are no cross-reactions with bilirubin, hemoglobin, immunoglobulins. The determination time is 5-10 minutes. There is no prozone effect. (Prozone is a situation in which, due to an excess of antigen or a lack of antibodies, the number of antigen–antibody complexes formed does not correspond to the true concentration of antigens.)ICED allows you to identify the immune status of the patient right at the doctor's appointment with the help of tests for immunoglobulin E.

The test for serum immunoglobulin E has a sensitivity of 150 IU/ml and a specificity of 90.9%.

There is no prozone effect up to 32,000 IU/ml. The determination time is 5-10 minutes.Rapid tests for thyroid-stimulating hormone (in whole and capillary blood, serum or plasma) are very important for endocrinologists.

This ICED test has children's and adult versions (with different threshold levels), it allows you to screen thyroid function right at the doctor's appointment. The adult version of the test has a threshold sensitivity of 5 microns / ml, children's – 10 microns / ml.

Specificity 97.3%, there are no cross-reactions with growth hormones, placental lactogen and choriogonadotropic hormone. The detection time is 10 minutes.Hormone tests for obstetrics and gynecology are very important and relevant.

These are tests for choriongonadotropin (in urine or blood serum), allowing to detect pregnancy already on the first day of cycle delay, for luteinizing hormone (in urine) to determine the exact time of ovulation, for follicle-stimulating hormone (in urine) and prolactin (in serum). It is essential that these tests can be carried out independently at home. The sensitivity of the HCG test is 5 mMU /ml in serum, 10 mMU/ml in urine.

Specificity is 100%, no cross–reactions are observed. The detection time is 5 minutes. There is no prozone effect up to 1 million mMU/ml.The sensitivity of the test for luteinizing hormone is 30 mMU / ml, at lower concentrations of LH, its detection is also possible.

Specificity is 100%, there are no cross–reactions with other hormones and products of their metabolism. There is no prozone effect. The detection time is 5 minutes.The sensitivity of the FSH test is 25 mMU /ml, specificity is 100%, there are no cross–reactions with other hormones and products of their metabolism.

There is no prozone effect. The detection time is 10 minutes.The sensitivity of the prolactin test is 37 ng/ml (800 mMU/l).

Specificity is 100%, there are no cross–reactions with growth hormones and placental lactogen. There is no prozone effect. The determination time is 5-10 minutes.Tests for cancer markers are very important.

These are tests for alpha-fetoprotein, for ferritin, which allows to detect the presence of anemia with hidden bleeding, for hidden blood in feces.And, perhaps, one of the most important tests is for prostate–specific antigen (PSA) (in serum, plasma and whole blood), which can be carried out at home.

Timely and regular use of this test allows almost 100% to avoid the negative consequences of very common prostate tumors, the increase in the incidence of which is observed all over the world. This test should be taken regularly by every man over the age of 50. In the EU countries, it is carried out in every pharmacy, and this helps to detect prostate pathology at an early stage. Unfortunately, in Russia, prostate cancer is diagnosed in most cases at the last, IV stage of the disease.The alphafetoprotein test has a threshold sensitivity of 10 ng/ml.

The detection time is 10 minutes.Ferritin can be determined by capillary blood Test sensitivity of 20 ng/ml.

The detection time is 10 minutes.The test for determining the presence of hidden blood in feces has a wide range of sensitivity – from 40 micrograms to 120 mg of hemoglobin per gram of feces.

Analysis time 10 min. The PSA test has a threshold detection level of 4 ng/ml and a detection time of 10 min.

Fig. 1. PSA test cassette, general view.

Dimensions 65×27×5 mm.How accurately the IHED works.

To make the answer obvious, a few words about how immunochromatographic tests work. Although the plates look very simple outwardly, this is the result of the most modern technologies for obtaining monoclonal and polyclonal antibodies to specific human immunoglobulins, to recombinant antigens of pathogens and the use of sorbents with improved properties. Fig. 2. The device of the test cassette.

Table 1. Performance characteristics of VEDALAB express tests Disease

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