What Is ZRT Hormone Testing

ZRT Laboratory hormone testing is a suite of diagnostic panels that use saliva, dried blood spot (DBS), and dried urine samples collected at home to measure steroid hormones, thyroid markers, adrenal hormones, and related metabolites. Developed by David Zava, Ph.D., ZRT was among the first clinical laboratories to validate saliva and DBS methods for hormone assessment. The panels are used by functional and integrative practitioners as well as individuals seeking accessible, repeated hormone monitoring outside of conventional venipuncture.

Hormones regulate nearly every physiological process relevant to aging: metabolic rate, body composition, bone turnover, cognitive function, mood, reproductive health, and cardiovascular risk. Subtle shifts in hormonal output or metabolism can precede overt disease by years, making early detection a meaningful tool for anyone interested in maintaining function over decades. Yet standard annual physicals rarely include comprehensive hormone panels, and when they do, a single fasting blood draw may miss dynamic patterns such as cortisol's diurnal curve or the pulsatile nature of sex hormone release.

ZRT testing fills this gap by enabling repeated, timed sample collection in the home environment. Because saliva and dried blood spots are stable at room temperature and ship easily, the barrier to longitudinal hormone tracking drops considerably. For people on bioidentical hormone replacement therapy, topical testosterone, or progesterone cream, saliva testing captures tissue-level hormone exposure that serum draws can underestimate or miss entirely. This practical accessibility makes ZRT a common entry point for individuals beginning to decode their own endocrine landscape.

ZRT offers three collection methods, each suited to different analytes. Saliva collection captures free (unbound) steroid hormones: cortisol, DHEA-S, estradiol, estriol, progesterone, testosterone, and others. Because steroid hormones enter saliva by passive diffusion through acinar cells, the concentration in saliva closely reflects the bioavailable fraction circulating in blood. This is particularly useful for cortisol, where four timed samples across a day reveal the diurnal rhythm that a single morning blood draw cannot.

Dried blood spot testing works by pricking a finger and applying drops to a filter card. The lab then elutes the sample and runs immunoassays or liquid chromatography/tandem mass spectrometry (LC-MS/MS) depending on the analyte. DBS is used for thyroid hormones (TSH, free T3, free T4, TPO antibodies), insulin, vitamin D, PSA, and several other markers that are difficult or impossible to measure in saliva. The dried format preserves analyte stability during shipping and avoids the logistical burden of serum separation.

Dried urine testing, available through ZRT's DUTCH-compatible panels, captures hormone metabolites and their downstream products. This method provides insight into how the body processes hormones through pathways such as 2-hydroxy, 4-hydroxy, and 16-hydroxy estrogen metabolism, or the 5-alpha reductase conversion of testosterone to DHT. By combining saliva, DBS, and dried urine in a single order, a practitioner can build a layered picture of production, bioavailability, and metabolism that no single specimen type offers alone.

ZRT panels can measure a wide range of hormones and related biomarkers depending on the specific kit ordered. Saliva panels typically include cortisol (morning, noon, evening, night), DHEA-S, estradiol, estriol, progesterone, testosterone, and in some panels, melatonin. Dried blood spot panels cover thyroid markers (TSH, free T3, free T4, thyroid peroxidase antibodies), insulin, hemoglobin A1c, PSA, sex hormone-binding globulin (SHBG), vitamin D (25-OH), and high-sensitivity C-reactive protein (hsCRP).

Dried urine panels extend the picture into hormone metabolism, reporting on estrogen metabolites (2-OH, 4-OH, 16-OH estrone and estradiol), androgen metabolites (androsterone, etiocholanolone, 5-alpha and 5-beta reduced androgens), cortisol metabolites, and organic acids related to neurotransmitter and nutritional status. Some comprehensive panels combine all three specimen types in a single kit, giving practitioners a layered view of hormone production, circulating bioavailability, and downstream metabolic processing.

Preparation depends on which panel you are running, but several principles apply broadly. Discontinue biotin supplements at least 72 hours before collection, as biotin can interfere with the immunoassay platforms used for many analytes. For saliva collection, avoid eating, drinking anything other than water, or brushing teeth for at least 30 minutes before each sample. If you use topical hormone creams, wash your hands thoroughly and avoid applying cream to your neck, chest, or face for at least 12 hours before saliva collection to prevent contamination.

For dried blood spot collection, warm your hands before lancing your finger to improve blood flow. Avoid collecting samples immediately after vigorous exercise, significant alcohol intake, or a night of poor sleep, as these can acutely alter cortisol, testosterone, and insulin values. Women who are still cycling should follow kit instructions regarding cycle day; most panels specify collection on days 19 to 21 of the menstrual cycle to capture the mid-luteal phase, when progesterone is at its physiological peak. Collect samples at the times indicated in the kit and ship the same day for optimal analyte stability.

ZRT reports present each analyte with a numeric value and a reference range, typically categorized into low, normal, and high zones. It is important to understand that saliva and dried blood spot reference ranges are not interchangeable with serum reference ranges from conventional labs; they are derived from population data specific to each specimen type. A saliva testosterone value, for instance, cannot be directly compared to a serum total testosterone value, because saliva reflects only the free fraction.

Context matters more than any single number. A cortisol curve that is flat (low in the morning and relatively unchanged through the day) tells a different story than one that is simply low across all four time points. Estrogen metabolite ratios from dried urine panels are sometimes flagged as clinically significant, but interpretation of these ratios should account for the individual's overall estrogen production, not just the relative proportions. Patterns across multiple analytes are more informative than isolated values. A practitioner experienced with ZRT's methodology can help distinguish clinically meaningful findings from normal biological variation.

For an initial baseline, a single comprehensive panel is a reasonable starting point. If results reveal imbalances and you make a meaningful intervention (lifestyle change, supplement, or hormone therapy), retesting after 60 to 90 days allows enough time for physiological adaptation while still catching the trajectory of change. For individuals on stable hormone replacement therapy, testing every three to six months is a common monitoring cadence until values stabilize, after which twice yearly may suffice.

Four-point cortisol testing may be worth repeating seasonally in individuals with significant stress-related symptoms, since the HPA axis responds to environmental and psychological shifts over weeks to months. Thyroid panels through DBS can follow the same schedule as conventional thyroid monitoring. Avoid testing too frequently; monthly retesting adds cost without improving clinical decision-making for most hormones, given the natural variability in hormone output from day to day.

ZRT Laboratory has published peer-reviewed work validating the correlation between their dried blood spot and saliva methods and conventional serum testing for analytes including thyroid hormones, vitamin D, testosterone, and cortisol. Several studies comparing DBS to venipuncture-derived serum have shown clinically acceptable agreement for TSH, free T4, and 25-hydroxyvitamin D. Saliva cortisol measurement has a broader evidence base beyond ZRT specifically; it is recognized by endocrine societies as a valid method for screening Cushing's syndrome and assessing adrenal function, and ZRT's platform uses the same underlying immunoassay principles.

Limitations exist. Saliva estradiol and progesterone values in individuals using topical hormone preparations can be disproportionately elevated compared to serum, a phenomenon attributed to tissue loading and salivary gland uptake. This can complicate dose titration unless the practitioner is experienced with saliva-specific reference ranges. Dried urine metabolite testing, while increasingly popular in functional medicine, has fewer head-to-head validation studies against gold-standard 24-hour urine collections or serum metabolite panels. The clinical significance of some metabolite ratios reported in these panels (such as the 2:16 hydroxyestrone ratio) remains debated in mainstream endocrinology. Overall, the evidence supports ZRT's methods as reliable screening and monitoring tools when interpreted by a knowledgeable clinician, though they are not universally accepted as substitutes for serum-based endocrine workups in all clinical scenarios.

Sample collection errors are the most common source of inaccurate results; contamination of saliva with blood from inflamed gums, improper timing of collection, or failure to follow fasting instructions can all distort values. Individuals taking oral hormone replacement may see exaggerated saliva levels due to first-pass mucosal absorption, requiring clinician awareness of this artifact. Over-interpreting minor variations between tests is a risk, as hormone levels fluctuate day to day and even hour to hour. Results from ZRT panels should not be used to self-prescribe hormones, and individuals with symptoms suggesting serious endocrine disease (unexplained weight loss, severe fatigue, menstrual cessation) should pursue evaluation with a qualified provider who can integrate imaging and additional testing as needed.