Firstly, combined serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) testing is primarily used in women to distinguish between primary and secondary amenorrhea. Patients with secondary amenorrhea often exhibit reduced serum LH levels. In men, these tests are used to distinguish between primary and secondary hypogonadism. Serum LH testing can also help to differentiate between true and false precocious puberty in prepubertal children. Elevated LH levels may also indicate polycystic ovary syndrome, Turner syndrome, primary hypogonadism, premature ovarian failure, post-ovariectomy and menopausal changes. Conversely, long-term use of oral contraceptives or hormone replacement therapy can lead to decreased LH levels. Low LH levels can directly impair corpus luteum function, leading to insufficient progesterone secretion and preventing the fertilized egg from implanting properly, which can result in recurrent miscarriages. Persistently low LH levels may also indicate problems with pituitary or hypothalamic function, causing menstruation to cease entirely.

The normal levels of LH (luteinizing hormone) can vary depending on gender, age and physiological stage. The normal ranges are detailed below:

（1） Women:

Follicular phase: 2–12.5 IU/L

Ovulation phase: 13–106 IU/L

Luteal phase: 0–10.5 IU/L

Postmenopausal: 7–65.2 IU/L

（2） Men:

luteinizing hormone 1.15–8.65 IU/L

Please note that these values are for reference only and that actual normal ranges may vary slightly depending on the laboratory and testing method.

Bear these points in mind:

Hormone secretion is closely linked to your lifestyle habits. Remembering these points will help you maintain a balanced endocrine system:

1. Don't stay up late! Getting 7 hours of sleep is more effective than any health supplement and is better for your endocrine system than staying up late.

2. Don't stress! High stress levels directly affect the secretion of pituitary hormones. Try taking a 10-minute meditative walk every day to give your emotions a break.

3. Balanced diet and don't go on a crash diet to lose weight. Extreme weight fluctuations can disrupt your hormones.

4. If you are experiencing irregular periods, prolonged infertility or recurrent miscarriages, get your hormone levels checked as soon as possible. The sooner you address the issue, the sooner you’ll conceive!

In fact, the luteinizing hormone (LH) acts as a 'barometer' for our reproductive health. There’s no need to panic if you see abnormal levels – early detection and intervention can help most situations gradually return to normal.