This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid and electrolytes, Subject name: Medicine
Hypokalemia is 
Select and explain. 
A. <3.5, B. <4.5, C. <5.6, D. <6.5
A: <3.5
Answer: A: <3.5 
Explanation: Hypokalaemia is a common electrolyte disturbance and is defined as existing when serum K+ falls below 3.5 mmol/L. The main causes of hypokalaemia Ref Davidson 23rd edition pg 363