Liddle's syndrome in MRCP

Liddle's syndrome in MRCP

I must say that there are a few genetic renal transport disorders which are popular in MRCP part 1 and 2. These are Bartter's syndrome, Gitelman's syndrome and of course Liddle's syndrome.

Liddle's syndrome is one of the rare causes of secondary hypertension. For you to understand better, you must know that our body maintains fluid balance mainly by controlling sodium homeostasis. However about 25000 mmol of sodium is being filtrated from our kidney everyday and it is crucial that majority of the sodium is being reabsorped from the tubule.

Although collecting duct is only responsible for 1-2% of total sodium reabsorption, it is the major site for our body to control the fluid status because it is the only site that is sensitive to our body hormone ( aldosterone)

Sodium is mainly being reabsorped via Sodium channel ( ENAc) at collecting duct. When aldosterone binds to mineralcorticoid ( MR) receptor, more ENac will be synthesized and more sodium will be reabsorped and more pottasium being excreted ( that explaines why primary aldosteronism patients have hypertension and hypokalemia)

Liddle's syndrome is just a genetic disorder when the ENac is activated all the time and sodium reabsorption is enhanced leading to hypertension and hypokalemia.

Hypercalcemia in MRCP(2)

Hypercalcemia in MRCP(2)

As a medical student many years ago, I remembered I have to memorize a lot of medical mnemonics. It is easy to remember how a patient with hypercalcemia presents to hospital, just remember this sentence,

“ STONES, BONES, ABDOMINAL MOANS, AND PSYCHIC GROANS”

Let me explain these symptoms briefly,

1) Stone-

I think it is rather straightforward, high calcium in the blood also translates high calcium in the urine, therefore you are prone to get stone. Besides that, patients with hypercalcemia also easily get dehydration because they might have polyuria due to nephrogenic diabetes insipidus.

2) Abdominal moans-

Hypercalcemia leads to constipation, abdominal colic and pancreatitis.

3) Bones-

You get bone pain because there is increased in bone resorption/ breakdown due to tumour ( causing pathological fracture) or hyperparathyroidism.

4) Psychic groans-

I can’t explain this, hypercalcemia can cause psychosis, confusion etc. You have to remember it!!But I think all the electrolyte imbalances can cause some kind of mental problems.

About the treatment of hypercalcemia, I think it is not so important to remember, anyway, remember the following strategies,
1) Rehydration

2) Steroids

3) Calcitonin

4) Biophosphonates

5) Plicamycin

6) Dialysis

7) And of course, treat the underlying cause!!

However, just want to remind all of you, there are a few causes of hypercalcemia that you might can’t explain the mechanism involved but they are important. These causes are thyrotoxicosis, Addison’s disease and acromegaly.

If you can explain the mechanism involved, please share with other readers!!

Hypercalcemia in MRCP (1)

Hypercalcemia in MRCP

As a houseofficer many years ago, I remember that there are two electrolytes that are frequently encountered during clinical practice- Potassium and Calcium.

We have discussed a lot about Potassium, I am going to talk about Calcium metabolism today and of course talk more about hypercalcemia.

It is pretty easy to remember, the only pool of calcium in our body is bone. Although tiny amount of calcium is being absorbed through the gut ( affected by Vitamin D), maintenance of normal calcium level in serum ( 2.2-2.6) greatly depends on exchange of Calcium between extracellular fluid and bone.


It is easy to remember that if we have low calcium level, our body will try to do the followings to increase calcium level in the serum,

1) Increase Calcium absorption from the gut
2) Increase bone resorption in the bone so that more calcium can be released to the serum
3) Reduce Calcium excretion from the kidney

The main organ that regulates these is parathyroid hormone. You can think of causes of hypercalcemia into a few big groups as below,

1) Bone problem
It is easy to understand this, when there is increased bone destruction, of course you calcium level is high. Therefore, any malignant disease either primary or secondary that leads to bone destructions can cause hypercalcemia.

2) Vitamin D problem
As I said before, Calcium absorption from the gut is mainly affected by Vitamin D, therefore, Vitamin D toxicity or granulomatous diseases ( such as Sarcoidosis or tuberculosis) can cause hypercalcemia.

3) Parathyroid hormone
Of course, when you have high parathyroid hormone ( primary and secondary), you calcium level is high but remember that secondary hyperparathyroidism may have normal or even low Calcium level.

4) Others
Some other rare causes such as Familial hypocalciuric hypercalcemia, milk alkali syndrome, immobility etc.

Arterial Blood Gas in MRCP (2)

Arterial Blood Gas in MRCP (2)


In my last post, I talked about Metabolic Acidosis and respiratory acidosis. Today I will cover metabolic alkalosis and respiratory alkalosis.

Take it easy because these two conditions are rare in your MRCP examination.

1) Metabolic alkalosis

The only one time you will be see metabolic alkalosis in your clinical practice is after patient has severe prolonged vomiting (especially in pyloric stenosis). This is because our gastric juice is acidic, where there is excessive loss of acid from our stomach, we turn alkalosis. You notice PH↓ and HCO3↑. You body may compensate by keeping more CO2 therefore there is a possibility that in your ABG, PaCO2↑



2) Respiratory Alkalosis

This is commonly seen in your clinical practice especially in A+E department but it is not an emergency. You usually see young ladies come to A+E complaining of shortness of breath but it is actually due to hyperventilation ( may be due to anxiety or not). However, never always assume that young ladies have hyperventilation when they complain to you that they are breathless. My old professor always told me that because some young ladies may also have pulmonary embolism ( due to risk factor of taking oral contraceptive pill or underlying autoimmune disease) when they are breathless. Therefore, always do an ABG if you are in doubt.

MRCP candidates always worried because in MRCP Part 1 and 2 examinations, they may show combination of abnormalities. There is always one rule to remember, if you can’t explain the abnormalities, always suspect this possibility.

Let me illustrate to you a case, let say a diabetic patient is admitted to you’re A+E due to cough and fever for 1 week and his CXR shows pneumonia. His ABG result is as below,

PH=7.2
HCO3=10
Random blood sugar = high
PaCO2=7 kpa
PaO2= 8kpa

Ok, from these first three results, we notice that this patient has metabolic acidosis ( PH↓, HCO3↓) and it is most probably due to diabetic ketoacidosis because the sugar is high as well. However, you will anticipate the PaCo2 to be low ( due to air hunger) but in this case the PaCO2 is high as well, you can’t explain that ( this is not a normal physiological respond) but from logical thinking, you know that this is a combination of metabolic and respiratory acidosis! ( Patient’s lung is also failing due to severe pneumonia and it is unable to compensate for the metabolic acidosis!)

Arterial Blood Gas in MRCP(I)

Arterial Blood Gas in MRCP (I)

Recently I received an email from a MRCP Part 1 and 2 blog reader about ABG interpretation in MRCP. I share with him the same feeling that ABG interpretation is important in MRCP as well as your daily clinical practice.

Our blood PH is closely regulated in a tight range around 7.4±0.05 so that our body can function properly. As you might remember during your secondary school time, enzymes function in certain PH range and will be damaged by acidic or alkaline environments.

Although a lot of candidates ( and a lot of house officers) tend to make various mistakes in ABG interpretation. I would like to give a few simple rules to remember so that you will not make any more mistakes in future,

1) There are two important organs in our body which control our body PH- lung and kidney.
2) Carbon dioxide is an acidic gas, therefore, in acidic environment ( due to various insults), our body ( the lung) tends to compensate by exhaling out more CO2 ( therefore, patient tends to hyperventilate) and vice versa.
3) HCO3 is alkaline and its level is mainly regulated in our kidney.
4) PH=7.4 is normal, if PH less than 7.35 is acidic and more than 7.45 is alkaline.
5) Remember other normal values, normal HCO3=22-28 mmol, PaO2 more than 10.6 kpa ( 1kPa=7.6mmHg), PaCO2=4.7-6.0 kPa ( 35-45mmHg)

OK, for you to interpret ABG results correctly, follow these simple steps,

1) Read the PH first, if PH<7.35, it is acidosis, if it is more than 7.45, it is alkalosis.
2) Once you know whether it is acidosis or alkalosis, you must determine eithet it is respiratory or metabolic, I find two useful parameters to look at, HCO3 and PaCO2.

Let me show you a few examples,

1) Metabolic Acidosis

I still think this is the commonest and most important acid-base balance disorder you will find in your MRCP and daily clinical practice. Read the causes for metabolic acidosis in my previous post.

However, in daily practice, you commonly find metabolic acidosis in uraemia ( chronic kidney disease patient) , diabetic ketoacidosis, salicylates poisoning and lactic acidosis.

Therefore, in metabolic acidosis, you will find PH↓, HCO3↓ and PaCO2↓, it is easy to understand, in metabolic acidosis, our body cannot conserve HCO3, therefore the level of HCO3 is low, however, for our body to compensate ( try to push up PH level), we will hyperventilate to blow out more CO2 ( because CO2 is acidic), therefore, patient will hyperventilate in metabolic acidosis. (air hunger)

You must remember that there are two types of metabolic acidosis- reduced anion gap and normal anion gap ( normal anion gap=8-16 mmol) metabolic acidosis, I have covered this topic in my previous post.

MRCP Question

A 16-year old girl is admitted to your ward from A+E department due to vomiting and abdominal pain. She has no known medical problems and denies taking any illegal drugs.

On examination, you noticed she is dehydrated, blood pressure=90/50, pulse rate=120 and her abdomen is soft. Below are her blood results,

Full blood count
Total white 16,000 ( Normal 4000-11,000)
Hb=12.3
Plt= 235,000

K= 3.2
Creatinine= 110
Na= 131
Cl=100

ABG ( on room air)
PH=7.21
HCO3= 12
PaO2= 12.2 kPa
PaCO2=2.5 kPa

Q: What is the diagnosis?
For the above ABG result, you know that the patient has metabolic acidosis and she presents with history of vomiting and abdominal pain, the first provisional diagnosis you should think of as a SHO is diabetic ketoacidosis!

2) Respiratory Acidosis

This is the second commonest acid-base balance problem you will see in your daily practice. Patients develop this because he/she is unable to blow out CO2 in the lung leading to accumulation of CO2 and respiratory acidosis. Therefore, our body will try to compensate by keeping more HCO3 via the kidney to buffer the acidosis. However, you must remember that kidney works somehow slower than the lung, therefore in acute respiratory acidosis (acute CO2 retention), you may find the HCO3 level is normal but in chronic CO2 retention ( such as in CAPD/COAD or chronic lung disease patients), the HCO3 level tends to be high.

This remembers me when I was a medical student where my lecturer liked to ask me way to help clinicians to differentiate COAD/COPD from asthma by looking at ABG results.

If you are a SHO on call in chest ward, a patient comes in with acute breathlessness and you notice he/she has rhonci all over the lung, you will most probably find the following ABG if you put patient on oxygen supplement,

PH ↓, PaO2 ↑, PaCO2↑ ( Respiratory acidosis)

For COAD /COPD, since that patients may have chronic CO2 retention, you will notice the HCO3 level tends to be high but in asthmatic patients, since it is an acute asthmatic attack that leads patient to have acute CO2 retention, you may find the HCO3 level to be normal ( kidney needs sometime to conserve HCO3, therefore in acute CO2 retention, the HCO3 level may be normal)

However, I must warn you that this rule is only for your reference only, there is no 100% in clinical medicine but I find this rule rather useful in daily practice.

I will talk about metabolic and respiratory alkalosis in my next post!