The SelectMDx urine test estimates the chance that a prostate biopsy would find prostate cancer, especially clinically significant cancer that is more likely to need treatment. It does not diagnose cancer on its own. Instead, it measures the activity of two genes in urine—HOXC6 and DLX1—and combines those molecular results with clinical factors such as PSA, age, prostate volume, and digital rectal examination findings. The test is mainly used after an abnormal or concerning PSA result to help decide whether further evaluation with prostate MRI and/or biopsy is warranted.
A lower-risk SelectMDx result can support a decision to avoid or delay biopsy in selected men, while a higher-risk result strengthens the case for imaging or biopsy. The result must still be interpreted alongside PSA trends, family history, MRI findings, examination, prior biopsy history, and personal preferences because no urine biomarker can completely rule cancer in or out.
- What it measures: urinary HOXC6 and DLX1 messenger RNA, combined with clinical risk factors to estimate prostate cancer risk.
- What a positive or higher-risk result means: the predicted chance of finding clinically significant prostate cancer on biopsy is increased, but cancer is not confirmed.
- What a negative or lower-risk result means: the chance of clinically significant cancer is lower, although important cancer can still be missed.
- How the sample is collected: current SelectMDx instructions generally call for a digital rectal examination immediately before collection of first-void urine.
- What usually happens next: clinicians combine the result with PSA, prostate MRI, examination, and overall risk before deciding about biopsy.
Table of Contents
- What the SelectMDx urine test measures
- Who may benefit from SelectMDx
- Collection and preparation
- How to interpret SelectMDx results
- Accuracy and limitations
- SelectMDx, MRI, and other prostate tests
- What to do after the result
What the SelectMDx urine test measures
SelectMDx is a risk-stratification test, not a stand-alone cancer test. It looks for increased expression of two messenger RNA markers, HOXC6 and DLX1, in prostate-derived material released into urine. Both genes are associated with prostate cancer biology, and higher expression can be associated with a greater likelihood of clinically significant disease.
The molecular measurements are not interpreted in isolation. The SelectMDx algorithm incorporates clinical information that affects prostate cancer probability. Depending on the current version and reporting system, this information can include age, serum PSA, prostate volume or PSA density, and digital rectal examination findings. The report then expresses risk in a way intended to help decide whether biopsy is justified.
This is different from the PSA blood test. PSA is a prostate-produced protein that can rise because of cancer, benign prostate enlargement, inflammation, urinary retention, or recent prostate manipulation. SelectMDx adds molecular information from urine to clinical risk factors in an effort to improve specificity for meaningful cancer.
The most important target is usually Grade Group 2 or higher prostate cancer. Grade Group 2 begins with a Gleason score of 3 + 4 = 7 and is commonly used as a threshold for “clinically significant” cancer in biomarker studies. This distinction matters because prostate screening can discover Grade Group 1 tumors that may never cause harm, while missing higher-grade disease has greater consequences.
SelectMDx therefore answers a practical question: Given this person’s molecular and clinical findings, how concerning is the risk that a biopsy will show significant prostate cancer? It does not determine tumor stage, show where a tumor is located, or replace the tissue diagnosis obtained from a biopsy.
Who may benefit from SelectMDx
SelectMDx is most useful when the decision about biopsy is genuinely uncertain. A common situation is a man with an elevated or rising PSA but no prior prostate cancer diagnosis, where the clinician wants more information before recommending an invasive biopsy.
Potential candidates can include men with:
- a PSA result that is above the expected range or increasing over time;
- an otherwise uncertain risk after history and digital rectal examination;
- a desire to reduce the chance of an unnecessary biopsy;
- an equivocal prostate MRI, such as a PI-RADS 3 lesion, in a setting where an additional biomarker may influence management;
- clinical risk factors that do not clearly point toward either immediate biopsy or routine follow-up.
A biomarker is less helpful when the next step is already clear. For example, a highly suspicious MRI lesion, a markedly abnormal examination, very concerning PSA kinetics, or another strong clinical finding may justify biopsy regardless of SelectMDx. At the other extreme, a person with very low baseline risk may not need another biomarker at all.
SelectMDx should also not be confused with a population screening test. PSA-based assessment remains the usual starting point for prostate cancer early detection. Biomarkers are generally considered secondary tests used after PSA or another finding creates uncertainty. Other secondary options include the percent-free PSA test, Prostate Health Index, 4Kscore, MRI, and other urine assays.
The best choice depends on local availability, cost, insurance coverage, previous testing, and how much the result is likely to change the decision. Ordering multiple biomarkers without a clear decision plan can create conflicting numbers without improving care.
Collection and preparation
The specimen is more structured than an ordinary urine sample. Current manufacturer instructions for SelectMDx generally require a digital rectal examination (DRE) immediately before urine collection. During the DRE, the clinician applies pressure and strokes each prostate lobe. This helps move prostate cells and prostate-derived material into the urethra, increasing the amount of target RNA available in the urine.
The patient then provides first-void urine, meaning the first part of the urinary stream after the DRE rather than a midstream clean-catch sample. A published prospective protocol collected approximately 30 mL after three strokes of each prostate lobe. Exact collection volume, transport medium, timing, and shipping requirements should follow the kit and laboratory instructions being used.
Before the appointment
There is usually no special diet for SelectMDx. The more important issue is whether recent prostate or urinary events could affect the overall clinical picture. Tell the ordering clinician about urinary infection symptoms, acute urinary retention, recent catheterization, cystoscopy, prostate biopsy, or other procedures. A recent biopsy can also affect eligibility under manufacturer collection instructions.
PSA should be interpreted thoughtfully as well. Ejaculation, vigorous cycling, prostatitis, urinary infection, retention, and prostate procedures can alter PSA in some men. If the PSA itself may be temporarily distorted, the clinician may prefer to repeat it before building a biopsy decision around the value. The total PSA test is only one part of the risk calculation.
A poorly collected specimen can produce an invalid or less reliable result. Because RNA is the analyte, the laboratory also has handling requirements for transport and processing. If a sample is rejected or reported as insufficient, repeating the collection is generally more appropriate than trying to interpret an unreliable score.
How to interpret SelectMDx results
SelectMDx reports risk rather than a simple diagnosis. The exact layout varies, but the clinically useful number is the predicted likelihood that biopsy would detect prostate cancer, particularly Grade Group 2 or higher disease.
A higher-risk or positive result means the combination of urine gene expression and clinical factors is more consistent with significant prostate cancer. It does not mean that cancer is definitely present. Benign findings can still occur on biopsy, and the positive predictive value changes with the population being tested and the person’s pretest risk.
A lower-risk or negative result means clinically significant cancer is less likely. This can support surveillance rather than immediate biopsy in an appropriate patient, but it is not a guarantee. Meta-analyses show that SelectMDx has useful sensitivity but imperfect specificity and does miss a minority of clinically significant cancers.
Published SelectMDx studies have used a continuous score and a validated cutoff. One large prospective strategy study described a score from about -6 to +6, with higher values representing higher risk, and used -2.8 as the positive cutoff. That threshold corresponded to an estimated 13% chance of finding high-grade cancer in that study. However, patients should use the risk percentages and interpretation on their current laboratory report, rather than applying an older research threshold to a newer assay version or different clinical setting.
A practical way to read the report
| Result pattern | What it generally suggests | Typical discussion |
|---|---|---|
| Lower molecular/clinical risk | Clinically significant cancer is less likely | Consider PSA follow-up, MRI context, and whether biopsy can reasonably be deferred |
| Intermediate or borderline risk | The test does not settle the biopsy decision | Use MRI, PSA density, family history, age, examination, and preferences |
| Higher molecular/clinical risk | Greater chance of Grade Group 2 or higher cancer | Discuss prostate MRI if not already done and whether targeted/systematic biopsy is appropriate |
A result can only be interpreted in context. For example, the same SelectMDx percentage may lead to different decisions in a healthy 55-year-old with a strong family history versus an 82-year-old with major competing health problems.
Why the urine result may disagree with PSA or MRI
Discordant tests are common because each test measures something different. PSA reflects prostate biology but is not cancer-specific. MRI looks for structural and tissue characteristics that suggest a tumor. SelectMDx measures expression of selected RNA markers and combines those data with clinical variables. A person can therefore have a high PSA with a low SelectMDx risk, or a negative MRI with a higher SelectMDx risk, without either test being “wrong.”
When results disagree, clinicians usually return to the underlying risk rather than choosing whichever test seems more reassuring. PSA density can help explain an elevated PSA in a very large prostate. MRI quality and radiologist experience matter, especially for small or anterior tumors. Infection or inflammation may complicate PSA interpretation. Family history, ancestry, germline cancer-predisposition variants, previous biopsy findings, and the pace of PSA change can also shift the threshold for biopsy.
A discordant result is therefore a reason for integration, not automatic repetition of every test. In some cases, repeating PSA under standardized conditions is sensible. In others, a high-quality MRI or biopsy is the most direct next step. The goal is to avoid both unnecessary procedures and false reassurance. A useful follow-up plan also specifies when the risk will be reassessed. Depending on age and baseline findings, that may involve repeat PSA within months rather than years, earlier MRI if PSA continues to rise, or direct biopsy when several risk signals point in the same direction. The appropriate interval is individualized rather than determined by the urine score alone.
Accuracy and limitations
SelectMDx improves risk estimation, but its performance is not perfect and varies across studies. A 2024 meta-analysis of 14 publications and 2,579 patients reported pooled sensitivity of about 81% and specificity of about 52% for clinically significant prostate cancer. A 2022 systematic review comparing SelectMDx with multiparametric MRI found pooled SelectMDx sensitivity of about 81% and specificity around 70% across its included studies, illustrating how estimates shift with study design, cutoff, cancer definition, and patient population.
Sensitivity describes how often a test is positive when significant cancer is truly present. Specificity describes how often it is negative when significant cancer is absent. Neither number tells an individual patient his exact probability. That probability also depends heavily on baseline risk.
Important limitations include:
- False negatives: clinically significant cancer can occur after a negative SelectMDx result.
- False positives: a positive result can lead to MRI or biopsy even when no significant cancer is found.
- Study heterogeneity: published cohorts differ in PSA ranges, biopsy history, MRI use, cancer prevalence, and definitions of clinically significant disease.
- Dependence on clinical inputs: prostate volume, PSA, examination, and sample quality can influence the calculated risk.
- Limited outcome evidence: most studies evaluate diagnostic accuracy and biopsies avoided, not whether biomarker-guided strategies improve long-term survival or quality of life.
For these reasons, SelectMDx should reduce uncertainty rather than create a new absolute rule. A sensible test is one that has a planned consequence: “If the result is low, I would defer biopsy; if it is high, I would proceed to MRI or biopsy.” If either result would lead to the same action, the test may add little value.
SelectMDx, MRI, and other prostate tests
Multiparametric prostate MRI and urine biomarkers answer different questions. MRI looks for a suspicious location within the prostate and can guide targeted biopsy. SelectMDx estimates risk from molecular and clinical information but cannot show where a lesion is.
In some studies, MRI has performed better as the main triage test, while SelectMDx has helped refine uncertainty before or after imaging. A prospective multicenter study of biopsy-naïve men found that using MRI for all participants avoided more biopsies and missed fewer high-grade cancers than a SelectMDx-only strategy. Other studies suggest combinations can achieve high sensitivity, but combining tests can also increase cost and complexity.
Urine tests are not interchangeable either. PCA3 urine testing measures a different prostate cancer-associated RNA marker. ExoDx Prostate testing evaluates exosomal RNA and uses a different collection and scoring approach. Blood-based tests such as PHI and 4Kscore use yet another set of biomarkers.
There is no universal “best” secondary test for every patient. The practical choice is the test with evidence in the patient’s clinical setting that meaningfully changes the next decision. MRI availability, prior negative biopsy, prostate size, kidney function, comorbidities, local expertise, and patient priorities all matter.
What to do after the result
The right follow-up depends on the combination of SelectMDx and the rest of the prostate cancer risk assessment.
A lower-risk result may support continued observation. That usually means a defined plan for repeat PSA, reassessment of PSA density or velocity, and reconsideration of MRI or biopsy if risk rises. “No biopsy now” should not be interpreted as “no follow-up.”
A higher-risk result commonly leads to discussion of prostate MRI and biopsy. MRI can identify suspicious lesions and help target cores, while systematic cores may still be recommended depending on the clinical scenario. Only biopsy can establish the histologic diagnosis and Grade Group of prostate cancer.
Seek prompt medical evaluation rather than relying on a biomarker if there are concerning urinary or systemic symptoms such as inability to urinate, fever with urinary symptoms, visible blood in the urine, severe new bone pain, or unexplained neurologic symptoms. These symptoms are not diagnosed by SelectMDx and may require a different workup.
Before making a decision, ask the clinician four concrete questions: What is my estimated risk of Grade Group 2 or higher cancer before this test? How did SelectMDx change that risk? What would MRI add? What are the tradeoffs of biopsy now versus repeat testing later? Those answers usually matter more than whether the report is labeled simply “positive” or “negative.”
If SelectMDx is repeated later, the new result should be interpreted alongside changes in PSA, prostate examination, MRI findings, age, and any new symptoms. A numerical shift by itself does not prove that cancer has appeared, disappeared, or changed grade. The important issue is whether the updated risk estimate crosses a threshold at which MRI, biopsy, or continued surveillance becomes the better choice.
References
- A meta-analysis for the diagnostic accuracy of SelectMDx in prostate cancer 2024 (Meta-Analysis)
- Evaluation of blood and urine based biomarkers for detection of clinically-significant prostate cancer 2025 (Review)
- Beyond blood biomarkers: the role of SelectMDX in clinically significant prostate cancer identification 2023 (Review)
- Accuracy of SelectMDx compared to mpMRI in the diagnosis of prostate cancer: a systematic review and diagnostic meta-analysis 2022 (Systematic Review)
- Blood- and urine-based biomarkers for the detection of clinically significant prostate cancer: a contemporary review 2025 (Review)
Disclaimer
This article is for general education and does not replace individualized medical care. SelectMDx results should be interpreted by a clinician together with PSA, prostate examination, imaging, medical history, and personal risk factors. A urine biomarker cannot by itself diagnose or exclude prostate cancer.
