| Meaning | ||
| M | murmur (heart murmur or heart attack that can cause death) | |
| MACE | Major adverse cardiovascular events | |
| MAC | Mycobacterium avium complex | |
| MAE | moves all extremities | |
| MAHA | microangiopathic hemolytic anemia | |
| MAL | midaxillary line | |
| MALT | mucosa-associated lymphoid tissue | |
| MANOS | minilaparoscopy assisted natural orifice surgery | |
| MAOI | monoamine oxidase inhibitor | |
| Mφ | macrophage | |
| MAP | ||
| MAR | ||
| MARSA | methicillin- and aminoglycoside-resistant Staphylococcus aureus | |
| MAS | Morgagni–Adams–Stokes syndrome meconium aspiration syndrome | |
| MAST | Michigan alcohol screening test | |
| MAT | multifocal atrial tachycardia microscopic agglutination testmedication-assisted treatment | |
| MBSS | modified barium swallow study | |
| MC | metacarpal bone | |
| MCA | mucinous cystadenomaMiddle cerebral artery | |
| MCAT | Medical College Admission Test | |
| MCC | MotorCycle Collision, Motor Cycle Crash | |
| MCD | minimal change diseaseharmful can cause cancer | |
| MCDK | multicystic dysplastic kidney | |
| MCP | metacarpophalangeal joint | |
| MCHC | mean corpuscular hemoglobin concentration | |
| MCH | mean cell hemoglobin | |
| MC&S | microscopy, culture, and sensitivity (the investigation steps in processing microbiology samples) | |
| MCTD | mixed connective tissue disease | |
| MCV | mean corpuscular volume | |
| MDCT | multidetector row computerized tomography | |
| MDD | major depressive disorder | |
| MDE | major depressive episode | |
| MDI | metered dose inhaler | |
| MDip | Master Diploma (specialization) | |
| MDS | myelodysplastic syndrome | |
| ME | UK: Myalgic Encephalopathy (= Chronic Fatigue Syndrome or "CFS") | |
| M/E | microscopic examination | |
| MEC | Moderate emetic chemotherapy | |
| MEDLINE | Medical Literature Analysis and Retrieval System Online (U.S. National Library of Medicine) | |
| MELD | Model for End-Stage Liver Disease | |
| MEN | multiple endocrine neoplasia | |
| MeSH | Medical Subject Headings (U.S. National Library of Medicine) | |
| MET | metabolic equivalent | |
| met | metastasis (pronounced like the word met; plural mets) | |
| MFM | maternal and fetal medicine | |
| Mg | magnesium | |
| MG | myasthenia gravis | |
| MGN | membranous glomerulonephritis | |
| MGPE | milligrams of phenytoin equivalents | |
| MgSO4 | magnesium sulfate (Do not use this abbreviation. Write out the name. Per the do-not-use list.) | |
| MGUS | monoclonal gammopathy of undetermined significance (unknown or uncertain may be substituted for undetermined) | |
| MHA-TP | microhemagglutination assay for T. pallidum | |
| MHMR | mental health and mental retardation | |
| MHW | Mental Health Worker | |
| MI | myocardial infarction | |
| MIC | minimum inhibitory concentration | |
| MICA | mental illness and chemical abuse; mentally ill chemical abuser | |
| MICU | mobile intensive care unit / medical intensive care unit | |
| MIF | Müllerian inhibitory factor | |
| MIP | Maximum intensity projection, a technique used to enhance CT, MRI, MRA, and PET images | |
| MIS | Minimally Invasive Surgery Müllerian Inhibiting Substance | |
| MLC | mixed lymphocyte culture | |
| MLE | midline episiotomy | |
| MM | myeloid metaplasia middle meningeal multiple myeloma | |
| M&M | morbidity and mortality | |
| MMFR | midmaximal flow rate | |
| MMI | maximum medical improvement | |
| MMK | Marshall–Marchetti–Kranz procedure | |
| MMM | moist mucous membranes Myelofibrosis with Myeloid Metaplasia | |
| MMP | medical marijuana patient Medical Monitoring Project (of the US CDC) | |
| MMPI | Minnesota Multiphasic Personality Inventory | |
| MMR | measles, mumps, and rubella combined vaccination mismatch repair | |
| MMR-D | mismatch repair deficiency syndrome | |
| MMSE | ||
| MMT | malignant mesenchymal tumor Mixed Mullerian Tumor | |
| MN | membranous nephropathy | |
| MND | motor neurone disease, also known as amyotrophic lateral sclerosis (ALS), Lou Gehrig's disease or Charcot disease | |
| MOB | mother of baby | |
| mod | moderate
| |
| MODY | maturity onset diabetes of the young | |
| Mo | monocytes | |
| MoM | multiples of the median | |
| MOM | milk of magnesia | |
| Mono-Di | monochorionic-diamniotic twins | |
| Mono-Mono | monochorionic-monoamniotic twins | |
| mechlorethamine, vincristine, procarbazine, and prednisone in combination (older treatment for Hodgkin's lymphoma) | ||
| MPA | medroxyprogesterone acetate | |
| MPD | Main pancreatic duct | |
| MPD(s) | myeloproliferative disease(s) | |
| MPGN | membranoproliferative glomerulonephritis | |
| MPO | myeloperoxidase | |
| MPT | multi-professional team | |
| MPV | mean platelet volume | |
| MR | medical representative mental retardation mitral regurgitation modified release (compare time release technology (medicine))menstrual regulation (unsafe abortion) | |
| MRA | magnetic resonance angiography | |
| MRCP | magnetic resonance cholangiopancreatography | |
| MRG | murmurs, rubs, and gallops (see heart sounds) | |
| MRI | magnetic resonance imaging | |
| MRSA | methicillin-resistant Staphylococcus aureus | |
| MS | medical student (MS-1, MS-2, MS-3, MS-4) mental status (see mental status examination) mitral stenosis multiple sclerosis | |
| MS-AFP | maternal serum alpha-fetoprotein | |
| MSD | musculoskeletal disorder | |
| MSDU | medical surgical day unit | |
| MSE | mental status examination | |
| MSH | melanocyte-stimulating hormone | |
| MSK | medullary sponge kidney musculoskeletal | |
| MSM | men who have sex with men | |
| MSMW | men who have sex with men and women | |
| MSO4 | morphine sulfate (Do not use this abbreviation. Write out the name. Per the do-not-use list.) | |
| MSOF | multisystem organ failure | |
| MSSA | methicillin-sensitive Staphylococcus aureus (contrast with MRSA) | |
| MSU | midstream urine sample (used in testing for presence of urinary tract infections) monosodium urate | |
| MSUD | maple syrup urine disease | |
| MT | metatarsal bone | |
| MTBI | mild traumatic brain injury | |
| MtF | Male to Female transgender person (trans woman) | |
| MTP | metatarsalphalangeal | |
| MTX | methotrexate | |
| MUGA | Multiple gated acquisition scan | |
| MUSE | medicated urethral system for erections | |
| MVA | motor vehicle accident | |
| MVC | motor vehicle crash | |
| MVI | Multivitamin | |
| MVo2 | mixed venous oxygen concentration | |
| MVP | mitral valve prolapse | |
| MVPS | mitral valve prolapse syndrome | |
| MVR | mitral valve replacement |