Which Testosterone Tests Do You Actually Need?

Start with the right test at the right time

For men with symptoms suggesting testosterone deficiency, clinicians generally start with a reliable early-morning total testosterone blood test. A second blood test on a separate morning is needed to confirm a low result. Fasting morning samples are commonly preferred, especially for initial diagnosis. Do not diagnose yourself from one afternoon reading or an unverified finger-prick result.

What is a low level?

The AUA uses total testosterone below 300 ng/dL as a reasonable diagnostic cutoff in men with compatible symptoms. Guidelines and laboratories differ, so do not treat 299 and 301 as completely different medical realities. Illness, sleep, timing, and testing methods can all affect results. A number without context is just a number.

When free testosterone matters

Most testosterone in blood is attached to proteins. Only a smaller portion is free. SHBG—sex hormone-binding globulin—can be unusually high or low because of age, obesity, liver disease, thyroid problems, and other factors. When total testosterone is borderline or SHBG may be abnormal, clinicians may measure SHBG and calculate free testosterone or use a reliable free testosterone method.

LH and FSH: finding the source

When low testosterone is confirmed, LH and FSH help distinguish a testicular problem from a brain–pituitary signaling problem. High LH often suggests the testicles are struggling to respond. Low or inappropriately normal LH with low testosterone suggests secondary hypogonadism. These findings guide what happens next.

When are prolactin, thyroid tests, and imaging useful?

Prolactin is often considered when secondary hypogonadism or low sexual desire is present, particularly when LH is low or normal. Thyroid tests, iron studies, or other workup may be appropriate based on symptoms and history. A pituitary MRI is reserved for particular patterns such as very low testosterone with secondary findings, abnormal prolactin, other pituitary problems, or concerning headaches and vision changes.

Before starting TRT

Clinicians commonly review blood count and hematocrit, blood pressure, fertility plans, prostate health and PSA when age and risk make it appropriate, sleep apnea, medical history, medication interactions, and cardiovascular risk. If pregnancy with a partner is a goal, testosterone therapy can work against that goal.

A practical testing checklist

• Relevant symptoms or signs?
• Two separate early-morning total testosterone measurements?
• Reliable lab and units recorded?
• SHBG/free testosterone when results are borderline or misleading?
• LH/FSH if confirmed low?
• Further tests selected for the individual, not ordered as an expensive bundle?
• Fertility and treatment safety discussed?

The takeaway

The best testosterone workup is not the largest one. It is the one that confirms whether you have deficiency, asks why, and protects you from the wrong treatment.