City Medicare Lab & City Diagnostic Center

City Medicare Lab & City Diagnostic Center


Typhoid / Enteric fever Diagnosis, Widal test and Its Procedure Lab TestsMicrobiology Sample It is done on the serum of the patient. A random sample can be taken. Purpose Of The Test (Indication) This test is done to diagnose enteric fever (Typhoid and paratyphoid fever). Pathophysiology History of widal test: In 1896 widal test was discovered by George-Fernand Widal for the diagnosis of enteric fever. Enteric fever includes typhoid and paratyphoid fever. Paratyphoid fever is milder than typhoid fever. Enteric fever also called as typhoid fever. Typhoid fever is caused by the bacterium Salmonella Typhi. Salmonella typhi has an incubation period of 14 to 21 days. Sometimes may even longer. 30% of the cases become chronic carriers due to persistent infection of the gallbladder. This has flagellar antigen H antigen and Lipopolysaccharides antigen is somatic or O antigen. Typhoid bacilli structure Typhoid bacilli structure The incubation period is 7 to 14 days. Typhoid fever is common in the developing world, where it affects about 21.5 million persons each year. Salmonella Typhi lives in humans and also found in chickens and eggs. It is present in the blood and intestinal tract. The carrier can harbor bacilli in the gallbladder. Both patients and carriers shed Salmonella Typhi in their feces (stool). Mode Of Spread Food: if food or drinks are contaminated. Spread from the carrier, who is shedding Salmonella Typhi. Contaminated drinking water: If sewage water is contaminated with Salmonella Typhi. Typhoid fever is more common in areas of the world where handwashing is less frequent. Once Salmonella Typhi bacteria are eaten or drunk, they multiply and spread into the bloodstream. Enteric fever pathogenesis Enteric fever pathogenesis Signs And Symptoms The patient has a fever and the pattern of the fever is typical. Fever is persistent and does not touch normally. This may be as high as 103 to 104 F. The patient may feel weak. May have stomach pains, headaches, or loss of appetite. In some cases, patients have a rash of flat type and rose-colored spots. Typhoid fever presentation and signs and symptoms Typhoid fever presentation and signs and symptoms The procedure of the Widal test Serial dilution of the patient serum is taken 1:40 to 1:320 Now add an equal volume of Salmonella antigen. This can be done as a Slide method or as a Tube method. When running in the tube then incubate tubes for 12 hours or overnight. Prepare the serial dilution as shown in the diagram. Widal test procedure and dilution Widal test procedure and dilution Widal test is done as follows and can read the result where there is the start of the agglutination, as shown in the following diagram. widal test result and interpretation widal test result and interpretation Drawback: This test will be positive after 7 to 10 days of Enteric fever. Serologically salmonella has 5 serogroups are A, B, C, D, E on the basis of O somatic antigen. On the basis of H-antigen are 1200 serotypes. 7 to 10 days antibody to D-somatic antigen appears. These antibodies against O antigens reach their peak by 3 to 5 weeks. H-flagellar antibodies appear later on. Widal test will be positive after 7 to 10 days of infection. The titer of O-antibodies 1:80 is suspicious in unvaccinated patients. The titer of 1:160 is strongly suggestive of infection in unvaccinated individuals. The titer of 1:40 for Antibody to flagellar-antigen (H) are suspicious in unvaccinated individual. While 1:160 are strongly suggestive. Titers are much higher in the vaccinated individual. Vi antigen for S.typhi is used to screen the carrier. antibodies to Vi-antigen are positive in Reading of the test The highest dilution of the serum is noted where there is agglutination. If it ends at 1:320 then that is the titer. The Widal test is positive if “O” antigen titer is >1:160 = active infection. If “H” antigen titer is >1:160, indicate past infection or in immunized persons. A fourfold increase in the titer (e.g., from 1:40 to 1:160) is diagnostic. O Antigen In the acute stage, Antigen O will be positive and titer will be more than 1:160. O antigen appears early and also disappear early. H Antigen H antigen rises late and disappears late. This will be positive in the recovery stage. Vi Antigen This is an indicator of the carrier stage. The false-positive test may be seen due to cross-reacting infections, including malaria. Other diagnostic tests for the diagnosis of Typhoid (Enteric) fever are: Blood culture, which will be positive in the first week when the Widal test is negative. Stool culture. 60 to 70% cases are negative during the first week and more cases positive in the third week of infection. Stool 90% of the cases are cleared of the bacteria by the 8th weeks of infection. Urine culture. Bone marrow culture. This is a very sensitive test. Bone marrow 90% of the cases are positive despite antibiotic therapy if these are ≤5 days. Another serological test is Typhidot. The gold standard is the blood culture where 90% of cases are positive in the first week. 50% of cases are positive by the third week. For better yield centrifuge the blood and take a buffy coat for culture. Other samples are stool, urine, Rose spot, bone marrow, and gastric or intestinal secretions. When culture is done simultaneously on blood, bone marrow, and intestinal secretions then positivity is >90%. Small % become the carrier and their stool culture remains positive for at least one year. Enteric fever diagnostic tests Enteric fever diagnostic tests Culture in Enteric fever patients from a different site: Time period Clinical S/S Blood Stool Urine Bone marrow During I.P 0 to 1 week diarrhea or constipation negative ± negative negative 1 to 2 weeks fever, headache, myalgia, cough 80 to 90% positive negative negative negative 2 to 4 weeks systemic toxemia 80 to 90% positive 80% positive 25% positive 90% positive 4 to 5 weeks recovering negative except in complications 50% positive 10% positive ± >5 weeks Cholecystitis, osteomyelitis negative except in complications ± ± negative Treatment The drug of choice is chloramphenicol but it has many side-effects. Ciprofloxacin is now a drug of choice. Ampicillin, amoxicillin, 3rd generation cephalosporins, and fluoroquinolones can be used. C0-trimoxazole is better than chloramphenicol with less side-effect. Carriers: It is difficult to treat carriers because of gall bladder involvement. Ampicillin is the most useful drugs but it is to be given in larger doses and for a longer period of time. Chloramphenicol is less effective than ampicillin. Ciprofloxacin can also be tried. The ultimate end is cholecystectomy. For Nonmedical person explanation of Widal test (Enteric fever): Please advise the Widal test if the fever persists more than 5 days at least. Just see the O antigen titer if it is 1:160, indicate Enteric fever. If O antigen is 1:80 then repeat the test after 5 to 7 days and now the titer is 1:160, rising titer again indicates acute infection. While H antigen does not indicate acute infection or acute enteric fever.
iabetes Mellitus – Part 6 – Diabetes Mellitus Complications and Work Up Chemical pathologyLab Tests Diabetic patients need follow-up and proper control to prevent diabetic complications. The Complication Of Diabetes Mellitus: There may be hypoglycemia. In patients with hyperglycemia of Type I, left uncontrolled may develop life-threatening complications like diabetic Ketoacidosis. Without treatment, the patient may become acidotic and dehydrated and may lose consciousness. Type II may develop hyperosmolar coma. Peripheral neuropathy. Diabetic retinopathy and cataract formation, it may lead to blindness. Cardiovascular microangiopathy. Coronary atherosclerosis. Myocardial infarction is 3 to 5 times more common in diabetic patients. AMI is the leading cause of death in patients with diabetes mellitus type 2. Peripheral vascular diseases like ischemia of lower extremities, erectile dysfunction, and intestinal ischemia. Gangrene of the foot. Diabetic kidney diseases, diabetic nephropathy. It may lead to renal failure. Chronic pyogenic skin infection. Candidal infection of the skin. Bone and joints show contracture. In the end, maybe result in stroke, gangrene, and coronary artery diseases. Diabetes mellitus complications Diabetes mellitus complications Diagnosis Fasting glucose level Random glucose level 2-hour glucose level (in OGTT) HbA1c Prediabetics 100 to 125 mg/dL 140 to 199 mg/dL 40 to 199 mg/dL 5.7 to 6.4% Diabetes mellitus > 126 mg/dL >200 mg/dL >200 mg/dL >6.5% The Complication Of Diabetes Mellitus: Acute complications are: There may be hypoglycemia. In patients with hyperglycemia of Type I left uncontrolled, they may develop life-threatening complications like diabetic Ketoacidosis. Without treatment, the patient may become acidotic and dehydrated and may lose consciousness. Type II may develop hyperosmolar coma. Chronic complications are: Peripheral neuropathy. Diabetic retinopathy and cataract formation. Cardiovascular microangiopathy. Coronary atherosclerosis. Myocardial infarction is 3 to 5 times more common in diabetic patients. AMI is the leading cause of death in patients with diabetes mellitus type 2. Peripheral vascular diseases like ischemia of lower extremities, erectile dysfunction, and intestinal ischemia. Gangrene of the foot. Diabetic kidney diseases (diabetic nephropathy), and may lead to end-stage renal disease. Chronic pyogenic skin infection. Candidal infection of the skin. Bone and joints show contracture. Work Up Of Diabetic Patients To Prevent The Complications: Basic metabolic panel : Fasting glucose level. Postprandial glucose level Microalbuminuria. BUN (urea). Creatinine. Electrolytes. Anion gap = (Sodium + potassium) — (Chloride + bicarbonate) HbA1c. Lipid profile: Cholesterol. Triglycerides. HDL. LDL.


[05/14/20]   Coronavirus and How to Boost Your Immunity


To fight the Coron virus, our body needs a very strong defensive system or immunity. In this pandemic of the Corna virus, we need to boost our immune system.

There is a major role in the diet containing well-balanced nutrients like a variety of fruits, vegetables, whole grains, seeds, nuts, and seafood.

Take the foods which are rich in:



Boost the immune system.

Role of free radicals:

Free radicals are unstable molecules that can damage the cells in our body.

These are basically unstable atoms which can damage the cells and lead to diseases.

These radicals are missing one electron and they take an electron from any of the cells (including immune cells) and cause damage to it.

Role of antioxidants:

In the body, our cells particularly immune cells are hit by free radicals, which is a harmful oxygen molecule are created in great numbers every day.

So these free radicals are missing one electron and these will get from any cells in the body. Whenever they get an electron from the cells, that cells will be dead or damaged.

Now, these antioxidants come in between the healthy cells and the free radicals. and prevents damage to the cells.

Anybody getting enough amount of the antioxidants will get sick 23 days per year, while the person deficient in antioxidants get sick 48 days per year.

Antioxidants and free radicals role

Antioxidants and free radicals role

Source of nutrient and antioxidants:


Vitamine C.

Vitamine E.

These foods also increase the killer cells of the immune system which can easily destroy the foreign material (antigen) which may be bacteria or viruses.

Beta-carotene: So we need the foods which are rich in beta-carotene for boosting the immune system are:


Winter squash.

Sweet potato.

Broccoli and kale.

Carrot one or two large has 15 to 30 grams of beta-carotene per day, and that is a sufficient amount of beta-carotene to boost immunity.

People getting 30 mg of beta-carotene per day will have more natural killer cells and virus-killing lymphocytes in the circulation.

Eating one sweet potato and one large carrot will give 30 mg of beta carotene. This will boost immunity.

Vitamin C is a powerful antioxidant. It boosts the immune system through the production of interferon which will destroy the viruses in the body.

Vitamin C also increases the glutathione which also makes the immune system strong.

Vitamin C also fight the colds and decrease the duration of illness.

The dose is variable some believe that 200 mg/day (DV) is the minimum dose.

Source of vitamin C:

Citrus fruits.




Rose hips tea.

Vitamin E has also a role in boosting immunity.

Vitamin E produces interleukin-2 which can destroy bacteria, viruses, and the cancer cells.

DV value of vitamin E is 30 IU.

Avoid high-fat food which increases the aging of the immune system.

It increases the cells damaging free radicals.

[05/02/20]   Safety in the Clinical Laboratory
Chemical pathologyLab Tests
The clinical laboratory has various types of safety hazards. Some of these may be very dangerous and life-threatening.

The people working in the laboratory must know what are various types of hazards in the laboratory, and also know what are the possible precautions to be taken to avoid those accidents.

The main type of hazards in the laboratory are:

Possible type of agent Source of the hazard Injury or effect
Physical agents a wet floor, heavy boxes, and people Sprains, fall, or strains
Sharp instruments Needle, lancets, and damaged glass Puncture, cuts, and exposure to pathogens
Fire / explosive Fire from burners, organic chemicals Burns
Chemicals Reagents and preservatives Carcinogens, Toxic materials, caustic agents
Electrical Wet equipment, ungrounded equipment, irregular electric cords
Biological Infectious agents (bacteria, viruses, parasites, fungal Bacterial, viral, parasitic, fungal infections
Radioactive material Radioisotope and radioactive agents Radiation injury

Possible Safety hazards
Possible Safety hazards

Physical Hazards:
These are quite common and these need to be avoided e.g.
Running in the rooms and hallways.
When the floor is wet, be careful.
Take care while lifting heavy objects.
Ladies should keep their long hair tight and on their backside.
Avoid loose jewelry.
Wear closed-toe shoes that provide maximum support.
Try to keep the working area neat and clean.
Also, keep the working area well-organized.
Sharp Edge Instruments:
Sharp edge instruments like a needle, broken glasses and lancets give rise to biological hazards like:
Give rise to blood born pathogens diseases.
These may give rise to bleeding.
Dispose of all these sharp edges articles in a safe place, like metal containers.
Cut the needle of the syringe by the cutter.
Also, crush the plastic syringes.
If you want to close the needle in the syringe then follow the following diagrammatic method.

Syringe Needle precautions while closing the syringe
Syringe Needle precautions while closing the syringe

Fire And Explosives:
In the laboratory, there are so many explosive and volatile chemicals used in the routine.
Flammable chemicals should be kept in the safety cabinet and explosion-proof refrigerators.
Compressed gas cylinders should be kept away from the heat.
The fire protection guidelines are given by the JCAHO.
Whenever fire erupts then following measures should be taken:
Rescue anyone in immediate danger.
Activate the institutional alarm.
Close all the doors of the fire area.
Try to extinguish the fire.
Fire blankets should be available in the lab.
Multiple purpose fire extinguishers may be used.
One can follow the guidelines given by the national fire protection association (NFPA).
Type of fire Extinguishing material
Wood, paper, clothing By simple water
Organic chemicals CO2, halon (CO2+bromine), dry chemicals
Combustible metals Sand
Electrical CO2, halon (CO2+bromine)
These should be labeled as carcinogenic, poisonous, or corrosive.
NFPA 704 gives the color coding for the materials. This color-coding will help the firefighter.
When mixing the acid and water, then first take the water and then add slowly the acid. Because by the addition of the acid there will heat production. If you add water to acid that may burst out.
safety acid to water to avoid accidents
Safety acid to water to avoid accidents

In the case of chemical spills, the best option is to flush the area with water.
Remove the contaminated clothes as soon as possible.
OSHA gives the written chemical hygiene plan (CHP).
It consists of:
Appropriate work practice.
Standard operating procedure.
Personal protective equipment.
Use of fume hoods and flammable safety cabinet.
Employee training equipment.
Medical consultation guidelines.
Label hazardous chemicals.
Electrical Hazards:
There are so many equipments working on electricity.
Avoid wet hands to operate the equipment.
Look after the damaged wires and avoid overload the circuits.
If any equipment becomes wet, then immediately unplug the wires and let it dry before using it.
Try to ground all the equipment.
If accidents occur and someone has electric shock, immediately shut off the electricity without touching the person or equipment.
Close the circuit breaker.
Move the equipment by some nonconductor objects like wood or glass.
Biological Factors:
Laboratory staff is always exposed to sources of potentially pathogenic microorganisms.
Most of the sample like blood, body fluids, urine, CSF, and tissues have pathogenic organisms.
The spread of infections may be by:
By direct contact of the laboratory staff. to the patient sample.
By inhalation of the infected material e.g. by droplet infection or if you are centrifuging the tube without caping it.
By ingestion of contaminated foods and water.
Then you may spread the infection to your colleagues.
Personel handwash and wearing personal protective clothes and pieces of equipment are important.
Special precautions are needed while handling the sample of a patient with HBV, HIV, and HCV viruses.
Wear gloves while collecting the blood from the possible case of a patient with HBV, HCV, or HIV.
Wear the face mask if there is any possibility of the splashing of the blood.
Dispose of all the sharp needles and objects in the puncture-resistant containers.
Follow the CDC universal precautions (UP).
In 1996 CDC combined the UP and Body surface isolation (BSI) and gave the guidelines:
Advised wash the hands after handling the blood or body fluids or secretions.
Wash hands immediately after removing the gloves.
Wear gloves when touching the blood, body fluids, secretions, excretions, and contaminated items.
Wear gloves when touching the mucous membranes or nonintact skin.
Change the gloves on the same patient if there is a possibility of a high concentration of pathogens.
Immediately remove the gloves and wash your hands before going to another patient.
Waer the mask, eye protection, and face shield to protect the mucous membranes of the eye, nose, and mouth during the procedure where there is any danger of the splash or spray of the blood, body fluids, excretions, and secretions.
Wearing the gown protects the clothes, and skin during the procedure.
If the gown is soiled, then remove it immediately and wash your hands to prevent others from the spread of infection.
Clean the patient care equipment and sterilize it.
Never recap the used needle, better to dispose of it. Or follow the direction given in the above diagram.
Most important in the case of prick or bleeding: Don’t stop the blood immediately, best is to bleed under the tap water as much as possible, and then use disinfectants and stop the bleeding.
Radioactive Materials:
This is needed in case using radioactive material like radioisotopes.
Mostly the radioactivity in the laboratory is very minimal and very little danger.
The best option is to wear a measuring device.
Exposure to pregnant ladies should be avoided because that will cause harm to the fetus.
The ladies should avoid such areas of radiation.
Possible References Used
Go Back To Chemical Pathology
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[04/28/20]   Arterial Blood gases (Blood Gases), Acidosis and Alkalosis (Acid-Base balance)
Chemical pathologyLab Tests
The better choice is the Radial artery.
The sample may be taken from the femoral artery or brachial.
Blood can be drawn from the indwelling arterial line.
The tests are done immediately because oxygen and carbon dioxide are unstable.
Place the sample on ice and immediately transfer it to the lab.
Arterial blood is better than venous blood.
For venous blood syringe or tubes are completely filled and apply a tourniquet for a few seconds.
Arterial blood is risky and it should be done by the trained person.
Never apply a tourniquet.
Don’t apply the pull to the plunger of the syringe.
Arterial VS Venous Blood
Arterial blood (ABG) gives a good mixture of blood from various areas of the body.
Arterial blood color is bright red.
Arterial blood measurement gives a better status of the lung oxygenation.
If arterial O2 concentration is normal, indicate lung function is normal.
If mixed venous O2 concentration is low, indicating heart and circulation are failing.
Arterial blood gives information about the ability of the lung to regulate the acid-base balance through retention or release of CO2.
The effectiveness of the kidneys in maintaining the appropriate bicarbonate level can also be checked.
Venous blood (VBG) gives information about the local area from where the blood sample is taken.
Venous blood color is dark red.
Metabolism of the extremity varies from area to area.
In shock, the extremities are cold and less blood perfusion.
During the local exercise of the extremities, as opening and closing the fist with power.
In case if there is an infection of the sample area.
A blood sample from the central venous catheter is not a good mix of the blood from various parts of the body. For well-mixed blood sample should be taken from the right ventricle or the pulmonary artery which is not an easy procedure.
A blood sample from the central venous catheter:
Shows low O2 concentration, it means that:
Either the lungs have not oxygenated the arterial blood well.
Or Heart is not circulating the blood effectively.
Difference between arterial and venous blood:
Biochemical parameters Arterial blood Venous blood
Use For blood gases For all routine lab test
Color Bright red Dark red
pH 7.35-7.45 7.32-7.43 (7.37)
pCO2 mmHg 35 -45 41 – 51
Bicarbonate mmol/L 22-28 23-29
pO2 mmHg 80-100 30 -40
O saturation 95% 70 to 75%
Precautions for the collection of blood

Avoid pain and anxiety to the patient which will lead to hyperventilation.
Hyperventilation due to any cause leads to decreased CO2 and increased pH.
Keep blood cool during transit.
Don’t clench finger or fist. This will leads to lower CO2 and increased acid metabolites.
pCO2 values are lower in the sitting or standing position in comparison with the supine position.
Don’t delay the performance of the test.
Avoid air bubbles in the syringe.
Excess of heparin decreases the pCO2 maybe 40% less.
Not proper mixing of the blood before running the test may give a false result.
A prolonged tourniquet or muscular activity decreases venous pO2 and pH.
Best way to collect arterial or venous blood anaerobically.
Arterial blood precautions:
Only syringe and needle, no tourniquet, no pull on the plunger.
Venous blood precautions:
Needle and syringe of the heparinized evacuated tube completely filled, drawn a few seconds after the tourniquet.
Liquid heparin is the only suitable anticoagulant with the proper amount.
Less amount will lead to clot formation.
The increased amount will lead to an increase in CO2 and a decrease in pH.
This will leads to a dilutional error.
Glass collection devices are better than plastic.
Purpose Of The Test (Indications)
This test is done on the mostly hospitalized patient.
Mostly the patients are on a ventilator or unconscious.
It monitors critically ill nonventilator patients.
For patients in pulmonary distress.
To assess the respiratory (ventilation), and metabolic (renal) acid/base and electrolyte imbalance.
Its primary use is to monitor arterial blood gases and pH of the blood.
Also used to monitor oxygenation.
Used to qualify a patient for use of oxygen at home.
This is used as preoperative baseline parameters.
Avoid in patients with coagulopathy.
Avoid in a patient with AV fistula.
The H+ ions concentration is commonly expressed as the pH.
The buffering system becomes active in response to change in the acid-base status.
Buffers can absorb excessive H+ (acid) or OH‾ (base) without any change in the pH.
The body normally maintains the arterial blood pH within a definite range of 7.35 to 7.45.
The H+ ions concentration must be regulated within the narrow range for the body to maintain the normal functionality of the body.
The slight change in the H+ concentration will change the body pH.
H+ is needed for the :
For the maintenance of cell integrity.
Speed of the enzymatic reaction.
The maintenance of the pH maintained by the interaction of three buffer systems in our body are:
Buffer system works through the retention or excretion of the H+.
Other minor buffer systems are phosphate and proteins.
The respiratory system works through Carbonic acid – bicarbonate (H2CO3 – HCO3¯). This will cover 80% of the pH control and rest is done by the renal system.
There is a ratio of one part of Carbonic acid (H2CO3) and twenty part of bicarbonate (HCO3−).
Buffer system, carbonic acid, and bicarbonate
Buffer system, carbonic acid, and bicarbonate

The carbonic acid level can be measured indirectly by measuring the pCO2 level.
The pCO2 is controlled by the lung.
More CO2 retained and more H2CO3 and will lead to acidosis.
Less CO2 and there will be fewer H2CO3 will lead to alkalosis.
Acid-base role of lung and kidney
Acid-base role of lung and kidney

The renal system works through excretion or retention of H+, HCO3-, Na+, K+, and Cl¯.
Acid-base maintenance
Acid-base maintenance and the buffer systems of the body

The body acids exist in two forms:
Volatile can be eliminated as CO2.
Nonvolatile. are sulphuric acid, phosphoric acid, and other organic acids. These are produced by the metabolism of protein, carbohydrates, and fats.
The volatile acid is carbonic acid (H2CO3) which will form by the hydration of the CO2.
Acid-base control by lungs and kidneys
Acid-base control by lungs and kidneys

In short lungs and kidneys, with the help of buffer systems, are the prime regulator of acid-base balance.
The process of respiration supplies oxygen to the tissues and removes the carbon dioxide produced by cellular metabolic activity.
External respiration:
Where oxygen in the air is exchanged at the alveolar level with carbon dioxide in the blood.
Internal respiration:
Take place at the tissue level, where oxygen in the blood is delivered to the cells, and carbon dioxide is transferred from the cells to the blood for the disposal.
Lung role in acid-base balance
Lung blood vessels role in acid-base balance

The medullary center, the brain stem controls the respiration by the increased CO2 and decreased O2.
Control of respiration rate

Hydrogen Ions And PH:
The H+ ions concentration is commonly expressed as the pH, The negative logarithm of H+ ions in the solution.
The logarithm value means that if the pH changes from 7 to 6, then the H+ ions change tenfold.
As the H+ ions increase the pH decreases, likewise if the H+ions decreases then pH increases.
The more H+ ions = the more acidic solution and lower pH.
The lower the H+ ions = the more basic solution and higher pH.
pH 7.4 = basic.
Different body fluids pH value Reason of the pH
Arterial blood 7.38 to 7.42 There is less H2CO3
Venous blood 7.37 There is more H2CO3
Cerebrospinal fluid 7.32 Decrease HCO3¯ and increased CO2
Urine 5.0 to 6.0 Increased H+ ions excretion
Pancreatic fluid 7.8 to 8.0 There are HCO3¯
Gastric contents 1.0 to 3.0 HCL production
Henderson- Hasselbalch equation give the idea about the blood gas measurement.
Henderson-Hasselbalch equation = pH = pKa + log (base/acid)
pH calculation formula

pH calculation formula
Example of H2CO3 / HCO3- Buffer system:
Where pH = 7.4
pKa = 6.1
Base (bicarbonate) = 24
Acid = dissolved PaCO2 = 0.03 x PaCO2 = 0.03 x 40 = 1.2
pH = 7.4 = 6.1 + log(24/1.2) = 6.1 + 1.3 = 7.4
The body makes every effort to maintain the validity of the above equation.
Our body will maintain pH 7.4 and pK is constant, so it can alter the bicarbonate and PaCO2 (H2CO3).
The body normally maintains the arterial pH between 7.35 to 7.45. This takes place through the buffer system of bicarbonate.
The negative logarithm of H+ ions in the solution.
Acid-base, Hydrogen role for pH

Acid-base, Hydrogen role for pH

Buffer pairs Buffer system pK value Chemical reaction
HCO3¯ / H2CO3 Bicarbonate/carbonic acid 6.1 H+ + HCO3 >< H2O + CO 2
HPO4- /H2PO4- Phosphate 6.8 H2PO4 ↔ H+ + HPO4-
Hb / HHb Hemoglobin 7.3 HHb ↔H+ + Hb
Pr- /HPr Protein in blood 6.7 HPr ↔ H+ + Pr-
CO2 and water react to form carbonic acid which then dissociates into hydrogen ions and HCO3–.
The pH is dependent upon the total concentration of:
Dissolved CO2.
H+ ions.
All these are inter-related.
The Active Buffer System In The Body Are:
Respiratory buffer system:
Bicarbonate (20 parts) / carbonic acid (one part) = (HCO3 / H2CO3) is the most important buffering system.
This buffer system works in the lungs and as well as in the kidneys.
The greater the CO2 partial pressure pCO2, the more carbonic acid (H2CO3) forms. This relationship can be expressed as:
H2CO3 = 0.03 x pCO2 (mm Hg)
0.03 represents the solubility coefficient for the CO2 in the water.
The pCO2 of the arterial blood is around 44 mm Hg. Therefore the amount of H2CO3 is equal to 1.2 mmol/L = 0.03 x 40 = 1.2 mmol/L
Acids or chemical substances can donate H+ ions.
Bases or substances that can accept H+ ions.
Strong acids readily give up H+, whereas strong base readily accepts H+.
Respiratory and metabolic disorder depends on the correct measurement of:
Acid/base assessed by:
Total CO2
Plasma pH
CO2 and H2O reaction
Acid-base, Hydrogen role for pH

The lungs can decrease the amount of H2CO3 by blowing off the CO2 and leaving H2O.
H2CO3 → CO2 + H2O
The kidneys can reabsorb HCO3¯or regenerate new HCO3¯ from the CO2 and water.
H2O + CO2 → HCO3¯ + H+
Renal regulation is slow / Pulmonary regulation is fast
Renal buffering system
The distle tubule of the kidney regulates the acid-base balance.
It secretes H+ ions into the urine and reabsorbs the HCO3¯.
H2PO4¯ and NH4+ are also secreted into the urine.
Acid-base role of kidney
Acid-base role of the kidney

Common acid/base disorder the example is:
Lactic acidosis and diabetic ketoacidosis.
Intermediate organic acids are lactic acid and β-hydroxybutyric acid.
These above acids metabolized to CO2 and water.
These may accumulate and cause acidemia.
Body acids are formed as end products of cellular metabolism. The average person generates acid 50 to 100 meq/day from the metabolism of protein, carbohydrates, and fats, and from the loss of base in the stool.
To neutralize this acid formation, the body needs to maintain the pH in the range, in that case, an equal amount of acid needs to be neutralized or excreted.
Now our various buffer systems come into play like:
Retention or excretion of H+ ions.
Respiratory system.
Renal system.
These systems are interrelated and work together.
The pH of a solution is the negative logarithm of the hydrogen ion activity.
pH = -logaH+.
Acid-base status of the body is assessed by:
While blood passing through the lung, O2 moves to blood, and CO2 goes into the lung.
Blood gases control

As the blood hydrogen concentration increases, the pH decreases, and if hydrogen ions decrease the pH increases.
The decrease of one unit of pH represents a 10 times increase in H+ activity.
The average pH of the blood of 7.40 is equal to H+ ions concentration of 40 nmol/L.
The pH of the plasma is regulated by the lungs and the kidneys.
Acid/Base control mechanism

The acids found in the blood are carbonic acid (H2CO3), dietary acids, keto acid, and lactic acid.
pH indicates acidity and alkalinity.
Respiratory or metabolic alkalosis, the pH will be high.
Respiratory acidosis or metabolic acidosis pH value will be decreased.
pH alkaline when it is >7.4.
pH acidic when it is 2 meq/L (>2 mmol/L)
Base deficit < – 2 meq/L (< – 2 mmol/L)
HCO3 22 to 26 meq/L (22 to 26 mmol/L)
Normal Picture = PH Normal, PCO2 Normal, HCO3 Normal.
Acidemia means arterial blood pH 7.4.
Alkalosis means a systemic decrease in H+ ions.
Respiratory acidosis
pH and HCO3 go in the opposite direction.
pH lower, pCO2 high, HCO3 high.
Seen in respiratory depression due to any cause.
Excessive retention of CO2.
Respiratory acidosis and compensatory mechanism
Respiratory acidosis and compensatory mechanism

Metabolic acidosis
pH and HCO3 go in the same direction.
pH low, pCO2 low, HCO3 low.
Seen in diabetes, shock, renal failure, and an intestinal fistula.
Metabolic acidosis and compensatory mechanism
Metabolic acidosis and compensatory mechanism

Respiratory alkalosis
pH and HCO3 go in the opposite direction.
pH high, pCO2 low, HCO3 low.
HCO3 is normal or slightly decreased.
Seen in hyperventilation.
Excessive loss of CO2.
Respiratory alkalosis and compensatory mechanism
Respiratory alkalosis and compensatory mechanism

Metabolic Alkalosis
pH and HCO3 go in the same direction.
HCO3 is >30 meq/L.
pH high, pCO2 high, HCO3 high.
Urine pH >7.0 (Unless there is severe hypokalemia).
Serum K is usually low.
Seen in sodium bicarbonate overdose, prolonged vomiting, and nasogastric drainage.
Metabolic alkalosis and compensatory mechanism
Metabolic alkalosis and compensatory mechanism


pH = < than 7.4 = acidosis.
pH = > than 7.4 = alkalosis.

pCO2 is high = acidosis then it is respiratory acidosis.
pCO2 is low = acidosis then it is metabolic acidosis.
pCO2 is low = alkalosis then it is respiratory alkalosis.
pCO2 is high = alkalosis then it is metabolic alkalosis.

HCO3 is high in respiratory acidosis.
HCO3 low in metabolic acidosis.
HCO3 is low in respiratory alkalosis.
HCO3 is high in metabolic alkalosis.
Calculation of Anion gap = Na (140 ) + K (4) — Cl (110 ) + HCO3(24) = 10 meq/L

Normal anion gap = 10 to 12 meq/L = < 12
Table showing the values of pH, HCO3, pCO2, and etiology:

Clinical condition pH HCO3 pCO2 Etiology
Metabolic acidosis 7.4 high high Vomiting
Respiratory acidosis 7.4 low low Anxiety and pain
Critical Values
Biochemical parameter Less than More than
pH 7.25 7.55
pCO2 20 mm Hg 60 mm Hg
HCO3 15 meq/L 40 meq/L
pO2 40 mm Hg
O2 saturation 75% or lower
Base Excess ± 3meq/L
Summary of the acid-base system:

Acidosis leads to coma and death due to depression of the CNS.
Alkalosis leads to irritability, tetany, and possible death due to the stimulation of the CNS.
Acidosis state is more threatening than the alkalosis.

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