What does “sensitivity” mean when testing for ovulation? What sensitivity level do I need? What are normal levels of LH? In this guide, OBGYN Kenosha Gleaton answers these questions and more.

 

By Dr. Kenosha Gleaton

Ovulation tests are used to understand your fertile window by measuring a hormone called LH (luteinizing hormone) in your urine. By measuring LH for several days (or an entire cycle), you can detect your LH peak or surge, which predicts when ovulation is likely to occur (usually within 24 hours). 

What does “sensitivity” mean when testing for ovulation?

Different brands of ovulation tests differ in sensitivity, which is measured in IU/L (international units per liter). Note: sometimes you’ll see IU/L, and sometimes mlU/L (milli-international units per litre). These are a straight one to one conversion, so are often used interchangeably. 

The sensitivity of a test indicates the minimum amount of LH in your urine that the test is able to detect. This minimum threshold ranges from 10 IU/L to 40 IU/L, but most tests on the market today have a sensitivity level of 25-30 IU/L. 

In the case of ovulation test sensitivity, a lower number means the test is more sensitive, meaning it can detect lower ranges of LH that would be missed on a test with a higher threshold. 

So, what sensitivity level do I need in an ovulation test? 

Throughout a woman’s cycle, LH levels can range from 1.9 - 14.6 IU/L, but during the fertile window can surge to 118 IU/L right before the egg is released. Because of this, most women only need a test with a sensitivity of 20-50 IU/L to capture that surge. 

A commonly-referenced 2017 study found that levels of 25–30 mIU/ml represent the best cutoff to predict ovulation during a fertile window. This study established a cutoff at 25mIU/ml, which could result in a dark pink test line for most women, which is considered a "positive" result. Referencing this darker test line to all testing (within one cycle) should identify if a peak or surge was captured. So for the vast majority of women, a sensitivity level of 25-30 IU/L is sufficient for predicting ovulation. 

If you track your LH using a test with sensitivity of 25 IU/L and never find a peak (a test line as dark as the control line), a higher sensitivity test may be a better fit. If this is the case, we highly recommend talking to your OBGYN to ensure that you are ovulating. 

What are normal levels of LH?

LH patterns vary greatly from one woman to the next. The normal range for a woman varies throughout her menstrual cycle. Here are normal ranges. Note that this level of granularity is tested via a blood test through your OBGYN:

  • Follicular: 1.9-14.6 IU/L
  • Mid Cycle: 12.2-118.0 IU/L
  • Luteal: 0.7-12.9 IU/L
  • Postmenopausal: 5.3-65.4 IU/L

Abnormally high levels of LH during non ovulatory times in your menstrual cycle may suggest a hormonal imbalance such as a pituitary disorder, polycystic ovarian syndrome, or menopause. Low levels of LH may mean you may have a pituitary disorder, anorexia, malnutrition, or are under extreme stress.

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When should I begin testing for ovulation?

Industry standard is to begin testing on day ten of your cycle. However, you may want to begin testing a day after your period ends to find a baseline result of LH present in your urine. The baseline of 0-10 mIU/mL (a faint pink test line) is then referenced until a peak or surge (dark pink test line) is detected. The darkest line (from consecutive testing in one cycle) is your LH peak or surge, and this is considered to be your fertile window—aka the best time to have sex to get pregnant.

What if my ovulation test line is always faint?

LH is always in your system, so you should always at least see a faint test result line. Impending ovulation is indicated when this line becomes as dark or darker than the control line. If you test for an entire cycle and consistently see only a faint line, then further testing may be needed to ensure you are ovulating.

How sensitive is the Natalist Ovulation Test?

The Natalist midstream ovulation test is a qualitative test with a sensitivity level of 25 IU/L. A 2014 study found that peak LH levels have a median range of 44.6 mIU/mL. So 25 IU/L is a very  sensitive cutoff that can detect a peak or surge for most women.