LOH most commonly stands for late-onset hypogonadism, a condition in which men produce significantly less testosterone as they age, leading to symptoms like low energy, reduced sex drive, and changes in body composition. The term also has a separate meaning in genetics: loss of heterozygosity, which describes a specific type of DNA mutation linked to cancer development. Here’s what both mean and why they matter.
Late-Onset Hypogonadism: The Basics
Late-onset hypogonadism is a syndrome where testosterone levels drop low enough to cause noticeable physical and mental changes. The International Society for the Study of the Aging Male defines it as a biochemical syndrome associated with advancing age, characterized by deficient androgen (testosterone) levels that may also come with decreased sensitivity to the testosterone your body does produce. Unlike hypogonadism that develops during puberty or from injury, LOH comes on gradually, often making it hard to pinpoint when symptoms started.
Testosterone naturally declines about 1 to 2 percent per year after age 30, but LOH refers specifically to cases where levels fall below a clinically meaningful threshold and symptoms are present. Not every man with lower testosterone qualifies. The diagnosis requires both persistent symptoms and confirmed low blood levels.
Symptoms of Low Testosterone in Aging Men
LOH symptoms fall into three broad categories: sexual, physical, and psychological. The sexual symptoms tend to be the most noticeable and are often what prompts men to seek help. These include reduced sex drive, difficulty getting or maintaining erections, and in some cases fertility problems.
Physical changes develop more slowly. You may notice less muscle mass, increased body fat, reduced body and facial hair, and loss of bone density. Some men develop breast tissue growth or experience hot flashes, similar to what women experience during menopause. Fatigue and a general drop in energy are among the most common complaints.
The psychological effects can be easy to dismiss or attribute to stress. Depression, irritability, trouble concentrating, and short-term memory problems all show up in men with LOH. Sleep disturbances are common too, which can make every other symptom feel worse. Taken together, these changes can significantly affect quality of life, even if no single symptom feels dramatic on its own.
How LOH Is Diagnosed
Diagnosis requires a blood test measuring total testosterone, taken in the early morning when levels are naturally highest. The American Urological Association considers a total testosterone level below 300 ng/dL (nanograms per deciliter) to be the threshold for low testosterone. European guidelines use a slightly different number: below 12 nmol/L for total testosterone, or below 220 pmol/L for calculated free testosterone.
One test isn’t enough. Guidelines require two separate early-morning measurements, ideally taken while fasting, both showing low levels before a diagnosis is made. This matters because testosterone fluctuates day to day based on sleep, stress, illness, and other factors. A single low reading could be a fluke.
Crucially, low numbers alone don’t equal a diagnosis. You also need to have symptoms consistent with testosterone deficiency. A man with testosterone of 280 ng/dL who feels fine and functions normally wouldn’t typically be diagnosed with LOH.
Treatment and What to Expect
Testosterone replacement therapy is the primary treatment for confirmed LOH. It’s available as injections, gels, patches, or pellets, and the goal is to restore testosterone to a normal range, relieve symptoms, and maintain characteristics like muscle mass and bone density. Most men notice improvements in energy and libido within a few weeks to months, though body composition changes take longer.
Treatment isn’t appropriate for everyone. Men who are trying to have children should not take testosterone therapy, as it can suppress sperm production. It’s also not recommended for men with prostate or breast cancer, recent heart attack or stroke (within six months), uncontrolled heart failure, untreated severe sleep apnea, or blood that’s already too thick (elevated hematocrit).
For men over 65, guidelines recommend a more cautious, individualized approach rather than routine prescribing. The decision should involve a clear conversation about potential risks and benefits, particularly if the primary symptoms are nonspecific, like fatigue or low mood, which have many possible causes.
Once treatment starts, regular follow-up is important. Doctors typically monitor testosterone levels to confirm the therapy is working, check blood counts, and track prostate health. A significant rise in prostate-specific antigen (PSA) during the first year of treatment warrants further evaluation.
Lifestyle Factors That Affect Testosterone
Weight plays a major role. Excess body fat, particularly around the midsection, actively suppresses testosterone production. Losing weight through diet and exercise can meaningfully raise testosterone levels, sometimes enough to resolve mild cases of LOH without medication. Sleep is equally important. Poor or insufficient sleep directly lowers testosterone, and improving sleep quality can produce measurable improvements. Regular resistance training, stress management, and limiting alcohol all support healthier testosterone levels as well.
These lifestyle changes won’t replace therapy in men with significantly low testosterone, but they’re a meaningful first step, and they improve outcomes even for men who do go on testosterone replacement.
LOH in Genetics: Loss of Heterozygosity
In genetics, LOH stands for something entirely different: loss of heterozygosity. This refers to a mutation where one of your two copies of a gene or DNA segment is lost. Normally, you carry two copies of most genes, one inherited from each parent. When LOH occurs, one copy is deleted, degraded, or otherwise eliminated, leaving only a single version.
This matters most in cancer biology. Your body has tumor suppressor genes that act as brakes on cell growth. You need both copies knocked out for those brakes to fail completely. If you inherit or develop a mutation in one copy, the second copy still protects you. LOH removes that backup. When the remaining healthy copy is lost, the cell loses its ability to control growth, which can trigger cancer development.
Why LOH Matters in Cancer Diagnosis
LOH is observed in over 90% of human cancers, making it one of the most common genetic features of tumor cells. Unlike some mutations that can reverse themselves, LOH is permanent: once that chunk of DNA is gone, it’s gone. This irreversibility makes it a reliable marker for distinguishing cancer cells from normal tissue.
Clinicians now use genome-wide LOH patterns to guide treatment decisions. In ovarian cancer, for example, the extent of LOH across the genome helps determine whether a tumor has a defect in its DNA repair machinery. Tumors with extensive LOH respond significantly better to platinum-based chemotherapy, and patients with this pattern have longer periods before their cancer progresses. This information helps oncologists choose the most effective treatment strategy based on the genetic profile of each patient’s tumor rather than relying on a one-size-fits-all approach.
LOH can be caused by several mechanisms: deletion of a chromosome segment, loss of an entire chromosome, or events during cell division where genetic material is exchanged or converted incorrectly. The specific mechanism matters less to patients than the practical result, which is that LOH testing is becoming an increasingly useful tool for personalizing cancer care.