Osmolal Gap

Osmolal Gap is the difference between measured serum osmolality and calculated serum osmolality.

It is typically calculated as: OG = measured serum osmolality - (2 X serum sodium + serum glucose + serum urea)

Where:

* 2 X serum sodium + serum glucose + serum urea = the calculated serum osmolality and all measures are in mmol/L.
* OG = osmolal gap

In US customary units the calculated osmolarity is: ( 2 x sodium ) + glucose/18 + BUN/2.8.

A normal osmolal gap is < 12 mmol/L.

Causes of an elevated osmolal gap are numerous. Several causes are:

* ethanol intoxication
* methanol ingestion
* isopropanol ingestion
* ethylene glycol ingestion


Anion Gap Increases in Ethylene Glycol Poisoning (as the unmeasured ion is Anion)
Anion Gap Decreases in Lithium Toxicity (as the unmeasured ion is cation)

What will happen to Osmolal Gap in both Conditions

Suppose a person has BOTH Etylene Glycol Poisoning and Lithium Toxicity (Hypothetical - say a person with MDP attempted suicide), his anion gap may even be normal (depending on the degree of the toxicities)

But the Osmolal gap will be very high

Tough Entrance Exams

Entrance Exams are not pass/fail exams. They are rank exams. So whether the paper is tough or easy is not that important.

Advantages of Tough Questions

• There will be less clustering of ranks and hence you will not miss the bus by one mistake. If it is a easy paper, you will go back by 150 ranks per mistake (for ranks 100 to 3000)

Disadvantage of Tough Questions

• Your brain has been tuned to get an instant depression when you see a question for which you don't know the answer. (this is due to the faulty school system in india) hence you are likely to make mistakes in other easy questions

Links for Statisticians

http://clinresearch.blogspot.com/

BMJ

Statistics at Square One
http://bmj.bmjjournals.com/collections/statsbk/index.shtml

Journal of Physiology and Pharmacology
http://www.jpp.krakow.pl

Applied Clinical Trials
to know click on the link below
http://www.actmagazine.com/appliedclinicaltrials/

Indian Journal of Pharmacology . To go on the journal site click on the link below
http://www.ijp-online.com/

The New England Journal of Medicine. Click on the link below
http://content.nejm.org

Anion Gap HAGMA LAGMA and NAGMA !!!

• Blood has a lot of Cations
• Blood has a lot of Anions

Total charge of Anions = Total Charge of Cations

So

Na + K + Unmeasured Cations = HCO3 + Cl + unmeasured Anions
Rearranging
Na + K - (HCO3 + Cl) = Unmeasured Anions - Unmeasured Cations
Anion Gap = Unmeasured Anions - Unmeasured Cations

Anion Gap = (Na + K) - (HCO3 + Cl)

Note that some books ignore the value of Calcium and calculate Anion Gap as Na - (HCO3+Cl)

• Unmeasured Anions: Means all anions other than HCO3 and Cl ----> lactate, phosphate, ketoacids , Albumin, Ethylene Glycol etc
• Unmeasured Cations: Means Ca, Lithium, Globulin

So
Anion Gap is Increased in

• Conditions with Increased Unmeasured Anions
1. Diabetic Ketoacidosis
2. Uremia
3. Lactic Acidosis
• Conditions with Decreased Unmeasured Cations
1. Hypocalcemia

Anion Gap is decreased in

• Conditions with Decreased Unmeasured Anions
1. Hypoalbuminaemia (theoritically)
• Conditions with Increased Unmeasured Cations
1. Increase in Globulin (multiple Myeloma)
2. Lithium Toxicity
• 
  

Easy way to solve MCQs

1. Check what is decreased / Increased

If that is Na / K / HCO3 / Cl it is Normal Anion Gap Metabolic Acidosis (also called NAGMA). The matter is settled. No doubt about that. Vomitting, Diarrhoea, Renal Tubular Acidosis etc come here

2. If there is an increase in Unmeasured Anions (lactate etc)
It is High Anion Gap Metabolic Acidosis (HAGMA)

3. If there is a decrease in Unmeasured Cations (Globulin etc)
It is High Anion Gap Metabolic Acidosis (HAGMA)

4. If there is an increase in Unmeasured Cations (lactate etc)
It is Low Anion Gap Metabolic Acidosis (LAGMA)

5. If there is a decrease in Unmeasured Anions
It is Low Anion Gap Metabolic Acidosis (LAGMA)

Any doubts !!!
Post in the comments section

Epidemiology for the Uninitiated

This is free full text book uploaded on BMJ which can be had from te following site
http://bmj.bmjjournals.com/collections/epidem/epid.shtml

35 free full text medical journals

These are available on the follwing site
http://medind.nic.in/