A deep tendon reflex is the quick, automatic muscle twitch that happens when a clinician taps a tendon with a rubber hammer — the knee-jerk is the one almost everyone has felt. In medical notes it gets abbreviated to DTR, and each response is graded on a scale from 0 to 4. The test costs nothing, takes seconds, and checks whether your sensory nerve, your spinal cord, and your motor nerve are talking to each other properly.
In this guide you’ll learn what those grading numbers actually mean, which nerve roots each reflex tests, what reduced or overactive responses can point to, and which blood tests doctors often order when reflexes look unusual — from thyroid function to vitamin B12 and blood sugar. Most reflex findings are far less alarming than they sound, and context matters more than any single number.
What does DTR mean?
DTR stands for deep tendon reflex. Clinicians increasingly prefer the more accurate name muscle stretch reflex, because the hammer is not really testing the tendon — it is stretching the muscle attached to it. The reflex was first described in 1875 by Wilhelm Heinrich Erb and Carl Friedrich Otto Westphal, and it has stayed in routine use for 150 years because it is safe, fast, free, and needs no equipment beyond a hammer.
The reflex arc, step by step
A deep tendon reflex is a monosynaptic reflex, meaning only two nerve cells and a single connection between them are involved. Tapping the tendon briefly stretches the muscle. A stretch sensor inside the muscle, called the muscle spindle, fires a signal along a sensory nerve into the spinal cord. There it connects directly to a motor nerve, which fires straight back and tells the muscle to contract. Your brain is not consulted — that is why the response is faster than thought and why you cannot fully suppress it.
Why this small test tells clinicians so much
Because that loop runs from muscle to nerve to spinal cord and back, and because the brain quietly dampens it from above, a problem almost anywhere in the nervous system can change the response. That makes the reflex a genuine screening tool rather than a party trick. Reflex testing sits alongside strength, sensation, and coordination checks in a standard neurological exam, and clinicians may also record a Glasgow Coma Scale score when alertness is in question.
How clinicians test deep tendon reflexes
The examiner taps a tendon with a reflex hammer weighing roughly 80 to 140 grams, then watches the muscle rather than the limb. Several hammer designs exist — Taylor, Queen Square, Babinski, Troemmer — and with proper technique any of them works. Some clinicians improvise with the rim of a stethoscope or even a fingertip when reflexes are very brisk.
Why relaxation matters more than the hammer
The single biggest factor in an accurate result is whether you are relaxed. A tense or rigid posture, or simply thinking hard about the test, can flatten a perfectly normal reflex. Your provider will usually position the joint at roughly 90 degrees, support the limb, and distract you with conversation. Testing is compared side to side immediately — right elbow, then left elbow — so that subtle differences show up.
The Jendrassik maneuver
If a leg reflex does not appear, the examiner may ask you to hook your fingers together and pull your hands apart while clenching your teeth. This is the Jendrassik maneuver. It works by occupying the pathways your brain uses to dampen the reflex, and by stopping you from unconsciously holding the muscle still. A reflex that only appears with this reinforcement is recorded differently from one that appears on its own.
The deep tendon reflex grading scale, from 0 to 4
In 1993 the National Institute of Neurological Disorders and Stroke proposed a standard 0-to-4 scale, which has since been validated and is now used almost universally. You will often see the grades written with a plus sign — 2+ rather than 2 — but according to StatPearls, adding or omitting the plus sign does not change the meaning of the grade.
| Grade | Official wording | What it means in plain language |
|---|---|---|
| 0 | Reflex absent | No response at all, even with reinforcement. If it is absent on both sides with nothing else wrong, it can still be normal for you. |
| 1 (1+) | Small, less than normal | A trace flicker, or a response that only shows up with the Jendrassik maneuver. |
| 2 (2+) | Lower half of the normal range | A clear, expected twitch. This is what most people mean when they say “normal.” |
| 3 (3+) | Upper half of the normal range | Brisker than average — but still inside normal, especially when both sides match. |
| 4 (4+) | Enhanced, more than normal | Exaggerated, and includes clonus — repeated rhythmic beats — when clonus is present. |
Why symmetry matters more than the number
This is the part most reflex charts leave out, and it is worth internalizing before you worry about a grade on your notes. Symmetrical reflexes anywhere from 1+ to 3+ are generally considered normal, as long as no other neurological signs come with them. What genuinely concerns clinicians is asymmetry — a 2+ on the left and a 2 on the right in the same exam is more meaningful than whether one examiner calls everything 2 and another calls everything 2+.
The grading intervals are subjective, based on every normal reflex that particular examiner has felt before. That is a real limitation, and clinicians know it. It is also why a reflex grade is never read in isolation.
The main deep tendon reflexes and the nerves they test
Five reflexes make up the core of the exam, each mapped to a specific segment of the spinal cord. This mapping is what allows a clinician to localize a problem — if the biceps reflex is diminished but the triceps is normal, the trouble is likely around C5 to C6. A sixth, the jaw jerk, tests the brainstem rather than the spinal cord.
| Reflex | Spinal level | Nerve | What you feel and see |
|---|---|---|---|
| Biceps | C5–C6 | Musculocutaneous | Tap in the crook of the elbow; the forearm bends. |
| Brachioradialis | C5–C6 | Radial | Tap the forearm near the wrist, thumb side; the forearm bends and rotates. |
| Triceps | C7–C8 | Radial | Tap just behind the elbow; the forearm straightens. |
| Patellar (knee-jerk) | L2–L4 | Femoral | Tap below the kneecap; the lower leg kicks forward. |
| Achilles (ankle-jerk) | S1–S2 | Tibial | Tap the Achilles tendon; the foot points downward. |
| Jaw jerk | Pons (brainstem) | Trigeminal, mandibular branch | Tap the chin with the mouth slightly open; the jaw closes. |
Generations of medical students have memorized these levels with a nursery rhyme: one-two, buckle my shoe; three-four, kick the door; five-six, pick up sticks; seven-eight, lay them straight — ankle jerk at S1 and S2, knee jerk at L3 and L4, biceps and brachioradialis at C5 and C6, triceps at C7 and C8. The rhyme rounds things off slightly: the knee jerk actually draws on L2 through L4, with L4 contributing most.
What abnormal deep tendon reflexes can point to
The central rule is simple, and it surprises most people because it runs backwards from intuition. Damage low down — in the peripheral nerves or nerve roots — reduces reflexes. Damage high up, in the brain or spinal cord, increases them. That is because the brain’s normal job is to dampen the reflex; interrupt the dampener and the reflex runs unchecked.
Reduced or absent reflexes
Hyporeflexia means a decreased response; areflexia means none at all. Both point toward the lower motor neuron side — the nerve roots and peripheral nerves. Peripheral neuropathy is the most common cause of absent reflexes, and it is typically driven by diabetes, alcohol use, uremia from kidney disease, vitamin deficiencies, amyloidosis, or toxins. Reduced reflexes also show up in hypothyroidism, hypothermia, cerebellar problems, and with beta-blocker medication. Guillain-Barré syndrome and Lambert-Eaton myasthenic syndrome are rarer causes.
It is worth repeating Cleveland Clinic’s reassurance here: reflexes vary from person to person, some people simply have weak reflexes, and most people with weak reflexes and no other neurological difficulty do not have a neurological disease.
Brisk or overactive reflexes
Hyperreflexia points toward the upper motor neuron side — the brain, brainstem, or spinal cord. It can be an early sign of a problem in the corticospinal tract, and it shows up in conditions such as multiple sclerosis, stroke, spinal cord injury, and amyotrophic lateral sclerosis. But hyperreflexia can also be a completely normal finding, particularly when it is present on both sides.
Clonus is the exception. Clonus means involuntary rhythmic beating of a muscle after a sudden stretch, and unlike brisk reflexes it is never a normal finding. It always warrants further evaluation. It is commonly seen after stroke or spinal cord injury, in cerebral palsy and multiple sclerosis, and can also follow ingestion of large amounts of serotonergic medication.
Blood tests often ordered alongside an abnormal reflex exam
This is where an exam finding turns into a lab request. Several of the conditions that blunt or sharpen reflexes are metabolic rather than structural — which means a blood draw, not a scan, is often the next step. Your reflex findings will usually be documented in the notes alongside a review of systems that helps guide which tests get ordered.
Thyroid function
An underactive thyroid is an established cause of sluggish reflexes, and it is both common and very treatable. To check it, your doctor will typically order a TSH blood test, and depending on the result may add a free T4 measurement to clarify how the thyroid gland itself is performing.
Vitamin B12
Vitamin deficiencies are on the standard list of causes of peripheral neuropathy and lost reflexes, and B12 is the classic culprit. Doctors investigate this with a vitamin B12 blood test. There is a catch worth knowing about: B12 can be functionally low even when the standard level reads normal, so clinicians sometimes also measure homocysteine levels, which rise when B12 is not doing its job.
Blood sugar and diabetes
Diabetes heads the list of causes of peripheral neuropathy, and a lost ankle reflex is one of its earliest detectable signs. Alongside fasting glucose, clinicians check glycated hemoglobin (A1c) results, which reflect average blood sugar over the preceding two to three months rather than a single morning.
Electrolytes and kidney function
Because charged minerals carry nerve impulses, electrolyte shifts change reflexes. A basic metabolic panel reports magnesium blood levels and total calcium values, both of which have documented effects on reflex responses. Magnesium is a particularly clear example: in pregnant patients receiving magnesium sulfate, new loss of reflexes is one of the first warning signs of magnesium toxicity, which is exactly why nurses check knee-jerks so often during those infusions.
Kidney disease matters too, since uremia — the build-up of waste products when kidneys underperform — is a listed cause of neuropathy. Screening measures creatinine in the blood, and laboratories also calculate eGFR results to estimate how well the kidneys are filtering.
When to see a doctor
Reflexes are not something you can usefully test on yourself, and a single odd grade on a note is rarely cause for alarm. What deserves attention is a change, especially a change with company.
- Seek urgent care for sudden brisk reflexes combined with weakness, slurred speech, or loss of balance — these can signal a stroke or spinal cord compression.
- Seek prompt evaluation for rapidly ascending weakness or numbness with lost reflexes over hours to days.
- Book an appointment for gradual numbness, tingling, or weakness in the hands or feet, particularly with diabetes.
- Mention reflex changes that follow a new medication, an injury, or a metabolic illness.
- Ask about clonus if a clinician has noted it, since it always merits follow-up.
Latest scientific advances
Research on reflex testing has focused on its biggest known weakness — that grading depends on one clinician’s judgment — and on making the humble ankle tap earn its keep as a screening tool.
Reflexes are one of the more reliable parts of the neurological exam
A 2025 study in the Journal of Neurology had eight different neurologists, each blinded to the others, examine the same patients using a standard motor neuron scoring system. Deep tendon reflexes were among the items the raters agreed on most consistently, while other signs — such as the facial reflex — showed almost no agreement at all. What this means for you: the reflex portion of your exam is one of the sturdier findings in the note, even though the grade itself is a judgment call. (Inter-rater reliability is simply a measure of how well different examiners, testing the same person, arrive at the same answer.)
The ankle reflex is a surprisingly strong screening test for nerve damage in diabetes
A 2023 study in Endocrine Journal tested 214 people with diabetes and compared simple bedside checks against nerve conduction studies, the reference standard. Pairing a short symptom questionnaire with the ankle reflex caught roughly nine out of ten people who genuinely had nerve damage, and the authors recommended exactly that combination for large-scale screening because it is quick and cheap. A 2024 study of 200 patients in Cureus pointed the same way: about a quarter had an absent ankle reflex, and neuropathy was strongly linked to higher A1c and fasting glucose. What this means for you: if you have diabetes, that tap on the ankle is doing real work, and it pairs naturally with your blood sugar results.
Machines are learning to grade reflexes objectively
A 2022 study in Medical and Biological Engineering and Computing recorded knee reflexes with motion and muscle-activity sensors in healthy volunteers and in people with spasticity or Parkinson’s disease. The researchers found that the speed at which the leg swings was the most stable measurement, and a computer model could sort responses into the right grade with high accuracy. What this means for you: nothing changes at your next appointment, but tools like this may eventually let clinicians track reflex changes over time as a number rather than an impression. (A model like this is trained on known examples, then tested on new ones to see whether it generalizes.)
Normal B12 does not always mean adequate B12
A 2026 case report in the American Journal of Case Reports described a 57-year-old man on metformin for type 2 diabetes who developed unsteady walking and diminished knee reflexes. His serum B12 came back normal — but his homocysteine was markedly elevated, revealing a functional deficiency, and he improved substantially with B12 replacement. A single case report is the weakest form of evidence and cannot tell us how often this happens. What this means for you: it is a useful reminder to discuss B12 monitoring with your doctor if you take metformin long-term and notice new numbness or balance trouble.
Glossary of key terms
| Term | Definition |
|---|---|
| DTR (deep tendon reflex) | The automatic muscle contraction produced by tapping a tendon. Also called the muscle stretch reflex. |
| Reflex arc | The nerve pathway that produces a reflex: sensory nerve in, spinal cord connection, motor nerve out. |
| Muscle spindle | A tiny stretch sensor inside a muscle. It starts the reflex when the muscle is suddenly lengthened. |
| Hyperreflexia | Reflexes that are stronger than expected. Usually points to the brain or spinal cord, but can be normal when equal on both sides. |
| Hyporeflexia | Reflexes that are weaker than expected. Areflexia means the reflex is absent entirely. |
| Clonus | Repeated rhythmic muscle beats after a sudden stretch. Unlike brisk reflexes, clonus is never considered normal. |
| Upper motor neuron (UMN) | Nerve pathways running from the brain down through the spinal cord. Damage here tends to increase reflexes. |
| Lower motor neuron (LMN) | Nerves running from the spinal cord out to the muscles. Damage here tends to reduce reflexes. |
| Jendrassik maneuver | Hooking the fingers together and pulling, to bring out a leg reflex that is hard to elicit. |
| Peripheral neuropathy | Damage to the nerves outside the brain and spinal cord, often causing numbness, tingling, and lost reflexes. |
Frequently asked questions
What does a 3+ reflex mean on my chart?
A 3+ sits in the upper half of the normal range — brisker than average, but not automatically abnormal. Many healthy people run brisk, and when both sides match and nothing else in the exam is unusual, a 3+ is generally left alone. It becomes more interesting to a clinician if it appears on one side only, if it is new compared with a previous exam, or if it comes with weakness, clonus, or coordination trouble. If you are worried about a 3+ in your notes, the useful question to ask is whether it was symmetrical.
Are absent deep tendon reflexes always a problem?
No. An absent reflex on both sides, with no other symptoms and no other abnormal findings, can be perfectly normal for that person. Reflexes genuinely vary between individuals, and some people have naturally quiet ones. Testing errors matter too — tension, poor positioning, or skipping the reinforcement maneuver can all flatten a real reflex. What raises concern is an absent reflex on one side only, or an absent reflex arriving together with numbness, weakness, or muscle wasting in the same area.
Does the reflex test hurt?
It should not. The hammer weighs only about 80 to 140 grams and the tap is brief. Most people feel a light knock and then an involuntary twitch that can feel slightly strange, since the limb moves without you deciding to move it. Some clinicians place a finger over the tendon and strike their own finger, which cushions the blow further. If a reflex test genuinely hurts, tell your provider — that is worth mentioning, and usually points to something tender in the joint rather than the reflex itself.
Why do nurses check reflexes during pregnancy?
Reflex checks are a monitoring tool for patients receiving magnesium sulfate, the medication used to prevent seizures in preeclampsia and eclampsia. Magnesium calms the nervous system, and if the level climbs too high, one of the very first warning signs is that deep tendon reflexes disappear. Because a knee-jerk takes seconds to check and requires no equipment, it gives the care team an early, repeatable safety signal — well before more dangerous effects appear. Losing reflexes on magnesium means the infusion should be stopped promptly.
Can vitamin deficiency cause reduced reflexes?
Yes. Vitamin deficiencies appear on the standard list of causes of peripheral neuropathy, which is itself the most common reason for absent reflexes. Vitamin B12 is the best-known example, and low B12 can affect both the peripheral nerves and the spinal cord. The reassuring part is that this cause is identified with a straightforward blood test and is often correctable with supplementation. Because B12 can occasionally be functionally low despite a normal reading, doctors sometimes add a homocysteine test to get a clearer picture.
Can reflexes change over time?
Yes, in both directions. They can improve when an underlying cause is treated — thyroid hormone replaced, B12 restored, blood sugar brought under control. They can worsen with progressive nerve disease or after an injury. Reflexes also tend to become slightly quieter with age, which is why an older adult with modestly reduced reflexes and no other findings usually needs no workup. This is exactly why clinicians compare against your own previous exams rather than a universal standard.
Sources
- Zimmerman B, Hubbard JB — Deep Tendon Reflexes — StatPearls, NCBI Bookshelf, 2023 — https://www.ncbi.nlm.nih.gov/books/NBK531502/
- Rodriguez-Beato FY, De Jesus O — Physiology, Deep Tendon Reflexes — StatPearls, NCBI Bookshelf, 2023 — https://www.ncbi.nlm.nih.gov/books/NBK562238/
- National Library of Medicine — Neurological Exam — MedlinePlus Medical Tests — https://medlineplus.gov/lab-tests/neurological-exam/
- Cleveland Clinic — Hyporeflexia: Definition, Causes, Symptoms and Treatment — Cleveland Clinic Health Library, 2022 — https://my.clevelandclinic.org/health/symptoms/24176-hyporeflexia
- Cleveland Clinic — Hyperreflexia: What It Is, Causes, Symptoms and Treatment — Cleveland Clinic Health Library — https://my.clevelandclinic.org/health/symptoms/24967-hyperreflexia
- Jacobsen AB, Fanella G, de Carvalho M, et al. — Variability of the Penn upper motor neuron score in amyotrophic lateral sclerosis: need for a revised score — Journal of Neurology, 2025 — https://doi.org/10.1007/s00415-025-12895-7
- Ma X, Li M, Xie H, et al. — Ankle reflex and neurological symptom score: a primary level screening method for diabetic peripheral neuropathy — Endocrine Journal, 2023 — https://doi.org/10.1507/endocrj.EJ23-0476
- Uslu S, Nüzket T, Gürbüz M, Uysal H — Electrophysiological and kinesiological analysis of deep tendon reflex responses, importance of angular velocity — Medical and Biological Engineering and Computing, 2022 — https://doi.org/10.1007/s11517-022-02638-5
- Francis D, Kotteeswaran K, Padinhare Veedu P — Severity of neuropathy-related disability and associated factors of diabetic peripheral neuropathy in a tertiary healthcare center — Cureus, 2024 — https://doi.org/10.7759/cureus.55568
- Zhang R, Gou L, Zhou X — Metformin-associated functional vitamin B12 deficiency presenting as subacute combined degeneration in a 57-year-old man with diabetes mellitus — American Journal of Case Reports, 2026 — https://doi.org/10.12659/AJCR.952205
Further reading
- HPI meaning: history of present illness
- ADL meaning: activities of daily living
- NAD meaning: no acute distress in notes
- A&O meaning: orientation assessment
- Hyperthyroidism: symptoms, causes, and treatments
Understand your lab results with BloodSense
Get your results interpreted in minutes
When reflexes come back sluggish or unusually brisk, the follow-up is often a blood draw rather than a scan — commonly a TSH to check the thyroid, a vitamin B12 level, and an A1c to look at blood sugar over recent months. BloodSense reads those results and explains each marker in plain language, so you arrive at your next appointment knowing what the numbers say and what to ask. BloodSense helps you understand your lab results; it does not diagnose, and it does not replace your doctor.
