Wednesday, April 19, 2017

Apt Test in Newborn: Maternal vs Neonatal Blood

We had few cases of suspected GI bleeding, admitted or referred to our NICU. One was case of Hematochezia and other was case of fresh blood in vomitus. Both babies were born to mother with Antepartum hemorrhage. The general condition of the babies were fine, and the vitals. There was no other reason for GI bleed at such early period in these neonates.

Generally, in absence of Apt test, we would get Sepsis workup, PT, aPTT, platelets done and baby would also be given IV antibiotics, Vitamin K and possibly FFP.
But a Simple test can prevent unnecessary interventions when history is clear and baby is well.

Vomiting of blood mixed content on first day or two in newborn is a commonly encountered problem. In Neonates, swallowed maternal blood is the most common cause in case of suspected GI bleeding. Blood can be either swallowed during delivery or swallowed from cracked maternal nipples during breast feeding. 1. As gastric transit is quick, newborn even present mimicking hematochezia or malena.

A simple bedside test can rule out lot of confusion and prevent unnecessary intervention, specially when amount is significant and requires evaluation. Apt test is useful for differentiating between newborn swallowing mother’s blood and fetal gastrointestinal bleeding. One is a benign condition and other is a worrisome one.

How is Apt Test done?
- non-quantitative method based on resistance of hemoglobin F to alkali denaturation. This test is useful ONLY on frankly bloody (red) stool or gastric specimens, not tarry (black) specimens.

Concept is- Fetal Hb is resistant to alkali denaturation.

Color change in Positive and Negative test. Alkali Denaturation Test

- false-positive result as oxyhemoglobin has been converted to hematin. 
- Visual judgement of color produced by test procedure may lead to error if only a small amount of blood is present. 
-Bilirubin containing meconium and possibly other substances may cause stool color interference. 2

Other Diagnsotic consideration should be
Midgut volvulus
Sepsis- DIC
Early onset hemorrhagic disease of Newborn
Stress gastic ulcer
Traumatic bleed- NG or CPAP induced nasal or gastric mucosal bleed.

In a sick newborn, just relying on Apt test does not seem logical and detail work up is needed.

Saturday, March 11, 2017

Immunization in Children- Basic concept

Immunization is defined as the procedure by which the body is prepared to fight against a specific disease. It is used to induce the immune resistance of the body to a specific disease.

Immunization is of two types:
1. Passive immunization
2. Active immunization.

1. Passive Immunization Passive immunization or immunity is produced without challenging the immune system of the body. It is done by administration of serum or gamma globulins from a person who is already immunized (affected by the disease) to a non-immune person.
Passive immunization is acquired either naturally or artificially.

Passive Natural Immunization- Passive natural immunization is acquired from the mother before and after birth. Before birth, immunity is transferred from mother to the fetus in the form of maternal antibodies (mainly IgG) through placenta. After birth, the antibodies (IgA) are transferred through breast milk. 

Passive Artificial Immunization - It is developed by injecting previously prepared antibodies using serum from humans or animals. This type of immunity is useful for providing immediate protection against acute infections like tetanus, measles, etc.

2.Active Immunization

Active immunization or immunity is acquired by activating immune system of the body.  Body develops resistance against disease by producing antibodies following the exposure to antigens. Active immunity is acquired either ◦naturally or artificially.

Active Natural Immunization
Naturally acquired active immunity involves activation of immune system in the body to produce antibodies. It is achieved in both clinical and subclinical infections

Active Artificial Immunization
Active artificial immunization is a type of immunization that is achieved by the administration of vaccines or toxoids.

Vaccination : The process of distributing and administering vaccines is referred to as Vaccination.

Types of vaccine

1. Live-attenuated (weakened) vaccines

These vaccines contain modified strains of a pathogen (bacteria or viruses) that have been weakened but are able to multiply within the body and remain antigenic enough to induce a strong immune response. ( Replicating Ag). The varicella-zoster vaccine, oral poliovirus (OPV) vaccine, or yellow fever virus vaccine are some examples of this type of vaccine.

Advantage are- Single dose is sufficient for immunization

Heterologous vaccines:  a sub-group of live attenuated vaccines produced from strains that are pathogenic in animals but not in humans.
-confers protective immunity against a pathogen that shares cross-reacting antigens with the microorganisms in the vaccine.
-Example cowpox virus that protects against smallpox in humans.

2. Killed- Inactivated Vaccines

To produce this type of vaccines, bacteria or viruses are killed or inactivated by a chemical treatment or heat. This group includes for example the inactivated poliovirus (IPV) vaccine, pertussis vaccine, rabies vaccine, or hepatitis A virus vaccine.

- Repeated dosing required.

3. Sub-unit vaccines
Instead of the entire microbe, subunit vaccines include only the antigens that best stimulate the immune system. In some cases, these vaccines use epitopes: the very specific parts of the antigen that antibodies or T cells recognize and bind to.
Because subunit vaccines contain only the essential antigens and not all the other molecules that make up the microbe, the chances of adverse reactions to the vaccine are lower.
Eg Hep B vaccine

4. Toxoid Vaccines

These vaccines are used when a bacterial toxin is the main cause of illness. When the immune system receives a vaccine containing a harmless toxoid, it learns how to fight off the natural toxin. ( non replicating Ag). The immune system produces antibodies that block the toxin. E.g Vaccines against diphtheria and tetanus.

Routes of Administration
Deep subcutaneous or intramuscular route (most vaccines)
Oral route (oral BCG vaccine)
Intradermal route (BCG vaccine)
Intranasal route (live attenuated influenza vaccine)

Scheme of immunization

Primary vaccination
One dose vaccines (BCG, measles, mumps, rubella, yellow fever)
Multiple dose vaccines (polio, DPT, hepatitis B)

Booster vaccination
To maintain immunity level after it declines after some time has elapsed (DT, MMR
Periods of maintained immunity due to vaccines
Short period (months): cholera vaccine
Two years: TAB vaccine (typhoid-paratyphoid A and B vaccine)
Three to five years: DPT vaccine (diphtheria, pertussis (whooping cough), and tetanus)
Five or more years: BCG vaccine(Bacillus Calmette–GuĂ©rin is a vaccine against tuberculosis)
Ten years: yellow fever vaccine
Solid immunity: measles, mumps, and rubella vaccines