Luteinizing hormone

Luteinizing hormone (LH, lutropin or lutrophin) is a sex hormone produced by the gonadotroph cells inside the anterior pituitary gland, where it is made. It is relevant in the bodies of both men and women. 

In females, LH triggers ovulation and the development (creation) of a temporary endocrine structure called the corpus luteum. This structure is found in all female mammals including humans. In males, LH has also been called interstitial cell–stimulating hormone (ICSH). In men it stimulates Leydig cell production of testosterone. It acts together with follicle-stimulating hormone (FSH), which means it acts synergistically with FSH in the body. 

 Predicting ovulation 
LH promotes high levels of progesterone compared to levels at other parts of the cycle. Luteinizing hormone levels are highest in women during the "LH surge" phase which occurs during ovulation, and is caused by high levels of estrogen (causing the negative feedback loop to switch to positive feedback, causing the brain/pituitary to release more LH). This makes the hormone useful in tests for predicting fertility and ovulation.  

The detection of a surge in luteinising hormone (LH surge) usually means that ovulation will happen soon (or is at its peak). This is correct for most women. Conception, or fertilization, has the highest chance of being successful if sperm enters the vagina (such as by sexual intercourse or artificial insemination) at around the same time or on the same day the woman is ovulating (2-5 days before, with the chance going up as it gets closer, or if done on the same day as ovulation). 

LH can be detected by urinary test kits. Tests are done daily, around the time when ovulation is expected.  A swing from a negative reading to a positive one in the test suggests that ovulation will occur (happen) witin 24–48 hours.  

Tests may be read manually using a colour-change paper strip, or digitally with the assistance of reading electronics.

Related pages
 Hormones: Peptide hormone, Follicle-stimulating hormone (FSH)
 Pregnancy

 References 

Category:Hormones
Category:Endocrine system
Category:Female reproductive system
Category:Male reproductive system
Category:Menstrual cycle