Rabbi Yehuda Finchas
Ralph has diabetes. He generally monitors his glucose with a continuous glucose monitor (CGM), but at times he needs to confirm a reading by pricking his finger and placing a drop of blood on a test strip. He also needs to inject insulin. Before Shabbat he asked, “Rabbi, I know that drawing blood is forbidden on Shabbat. So how do I check my blood sugar? And what about injecting my insulin?”
Drawing Blood Is a Melachah
Drawing blood on Shabbat falls under the Torah prohibition of chovel, causing a wound. Yet not every instance of bleeding has the same halachic status.
The Or LeTzion (vol. 2, ch. 36:21) distinguishes between blood that emerges incidentally and blood that is intentionally extracted because the blood itself is needed. When blood is drawn for testing, the blood is actually being used: without the sample, the test cannot be performed. He therefore considers this a melachah hatzerichah legufah (an act that matches the constructive intent of that melachah) and rules that such blood may be drawn on Shabbat only for a patient whose condition involves danger.
This explains Ralph’s glucose testing. When he pricks his finger, he does not merely cause a tiny wound; he needs the resulting blood in order to determine his glucose level. The fact that the blood is discarded afterward does not change matters.
Hacham Ovadia Yosef, zt”l, explains that where glucose monitoring is medically necessary to prevent a potentially dangerous deterioration, pikuach nefesh overrides Shabbat (Hazon Ovadia, vol. 3, p. 373). Ralph should therefore perform the testing he medically requires for pikuach nefesh. Shabbat itself commands us to protect life. One does not become “more observant” by skipping this necessary monitoring.
An Injection Without Drawing Blood
Ralph’s insulin injection, however, is halachically different from his glucose test. The Or LeTzion (vol. 2, ch. 36:20) writes that an intramuscular or subcutaneous injection is permissible when needed for a sick person because ordinarily no blood is extracted. The medication is introduced into the body, but blood is neither intentionally removed nor needed for any purpose, this a melachah she’einah tzerichah legufah. Such an injection is therefore not comparable to drawing blood for a test.
Accordingly, Ralph may administer the insulin that he medically requires on Shabbat. In his case, there may in any event be considerations of pikuach nefesh. But the injection itself is less problematic than his glucose test because no blood ordinarily needs to be extracted or used.
What About Intravenous Injections?
Sometimes an intravenous injection requires drawing back a small amount of blood to confirm that the needle has entered the vein. Here too, the Or LeTzion permits the procedure for a patient even though blood is drawn, since the blood is not needed or used diagnostically. He therefore regards its extraction as a melachah she’einah tzerichah legufah and also as mekalkel, destructive rather than constructive activity. Hacham Ovadia Yosef, zt”l, similarly endorses permitting injections for a patient on Shabbat, including intravenous injections, in Yabia Omer (vol. 9, Orach Chaim 108:178), and notes that the Tzitz Eliezer reaches the same conclusion.
Conclusion
Ralph’s two procedures illustrate the distinction clearly. His glucose test intentionally extracts blood and uses it for testing. When such monitoring is medically necessary because of possible danger, it is permitted under pikuach nefesh. His insulin injection does not require blood to be extracted and is therefore permitted for a choleh even when there is no pikuach nefesh.
Rabbi Yehuda Finchas is a worldwide expert, lecturer, and author on Medical Halacha. He heads the Torat Habayit Medical Halacha Institute. He is the author of Brain Death in Halacha and the Tower of Babel Syndrome and his latest book is Nutrition and Hydration in Halacha. To contact Rabbi Finchas, email [email protected].