What comes out of the body:
20- Blood donation:
Most of contemporary scholars measure this issue to the issue of invalidating the fast by cupping, which is controversial among scholars. The majority of scholars i.e., the Hanafi, Maliki, and Shafa`is hold the view that it does not affect the fast. However, some scholars hold the other view that it invalidates the fast; this is the famous view of the Hanabali school of Fiqh and the chosen view of Shaykh Al Islam.
Based on this disagreement, scholars have differed as to blood donation. The most correct view is: the ruling is different in blood donation and the ruling must be according to the amount of the taken blood. If the donated blood is much, it invalidates the fast and if the amount is little, it does not affect the fast. This view considers the reason for invalidating the fast by cupping. Al Bukhari reported in his Sahih (book of authentic Hadiths) on the authority of Thabit Al Bannany that he asked Anas ibn Malik (may Allah be pleased with him) saying: "Did you hate cupping during the Prophet's lifetime? He Said: No, except if it causes weakness." [Reported by Al Bukhari]. You may understand that if you ponder over the saying of the Prophet (peace be upon him): “Whoever cannot help vomiting shall not make up for that day (in which he vomited), but the one who vomits deliberately should make up for that day." [Reported by Imam Ahmad, Abu Dawud and At-Tirmidhy with authentic chain of narration]. Anyone deliberately vomits has to make up for that day because vomiting causes weakness and fatigue to the body. It is well known that taking much blood in donation causes weakness and fatigue to the body; therefore, it invalidates the fast according to this condition.
21- Taking blood for analysis:
When the blood taken for analysis is little and it has been stated in the previous issue that the reason for invalidating the fast is the amount of blood which causes weakness and fatigue to the body, many scholars have adopted the view that taking blood samples for analysis does not affect the fast, which is the most correct view.
22- Taking samples (biopsy) of the liver or other organs:
The International Islamic Fiqh Academy reached a decision that such an act invalidates the fast if the instrument used in this process is not covered by solutions or fatty substances.
Finally, a Muslim doctor should advise the patient to delay things