A 12-year-old girl presented to her pediatrician for fatigue and postprandial abdominal pain. Laboratory tests revealed microcytic anemia and fecal occult blood test was positive. Esophagogastroduodenoscopy and colonoscopy were unremarkable. Capsule endoscopy demonstrated a 2.9 cm pedunculated polyp located in the jejunum which was surgically resected.

Figure 1
Figure 2

Based on the history and photomicrographs, which one of the following diagnoses is correct?

  • Juvenile Polyp
  • Peutz Jeghers Polyp
  • Cowden Syndrome Polyp
  • Intestinal-type adenoma, low grade dysplasia

The correct answer is ...

The correct answer is: Peutz Jeghers Polyp.

The correct answer is Peutz Jeghers (PJ) polyp, which is a type of hamartomatous polyp associated with Peutz Jeghers syndrome (PJS). PJS is an autosomal dominant cancer syndrome, with a prevalence of 1 in 200,000 individuals. The underlying genetic abnormality is an inherited germline mutation in the STK11 tumor suppressor gene encoding a serine/threonine kinase. Individuals with PJS present with mucocutaneous melanin pigmentation, gastrointestinal polyps, and increased risk of cancer of the following sites (listed in decreasing order of cancer risk): breast, colorectal, pancreas, stomach, ovary, lung, small intestine, uterus, testis, and cervix. It is important to note that PJ polyps are typically not precancerous.1,2  

Clinical diagnosis of PJS can be made, according to the WHO criteria, when a patient presents with three or more PJ polyps; one or more PJ polyps and a family history of PJS; mucocutaneous pigmentation and a family history of PJS; or one or more PJ polyps and mucocutaneous pigmentation.1 It is important to note that PJ polyps can occur as a solitary polyp in individuals without a family history of PJS or mucocutaneous pigmentation. In this circumstance, the significance is uncertain; however, one study examined 51 patients with a solitary PJ polyp and found that 35% of the patients were diagnosed with cancer (gastrointestinal, breast, lung, thyroid, prostate, hypopharyngeal, and liver) prior to the identification of the PJ polyp. The study suggests that if a patient with a solitary PJ polyp undergoes complete evaluation of the gastrointestinal tract and no other polyps are found, then the patient may not require additional surveillance.3 Most likely the patient presented in the above vignette had a solitary PJ polyp. She was referred to department of genetics to determine the next course of action.

PJ polyps are predominately found in the small intestine, but occasionally can be identified in the colorectum and stomach. Histologically, small intestinal and colorectal PJ polyps exhibit a very characteristic villous architecture with smooth muscle cores arborizing throughout the polyp. Lobular crypt organization is also a helpful feature to diagnose PJ polyps, but is more frequently identified in colorectal PJ polyps.4 Cystically dilated glands with mucin and misplacement of epithelium due to prolapse can also be seen. The epithelium lining the polyp is small intestinal type or colonic epithelium, depending on the polyp’s site of origin. Dysplastic change within the epithelium is very rare. 1

The histology seen in gastric PJ polyps is not as characteristic as seen in small intestinal or colorectal PJ polyps. The gastric PJ polyps frequently appear as juvenile polyps or sporadic hyperplastic polyps of the stomach.1

Cowden syndrome (CS) is an autosomal dominant cancer disorder caused by a germline PTEN mutation. CS polyps are morphologically diverse and include the following: hyperplastic polyps, hamartomatous/juvenile polyps, adenomas, and ganglioneuromas.1,5 Overall, hamartomatous CS polyps are more commonly found in the colon, are sessile, have a fibrotic lamina propria, and do not demonstrate surface erosion or cystically dilated glands. Specific features, if identified, that can help diagnose a CS hamartomatous polyp is the presence of ganglion cells and/or a nerve fiber proliferation in the lamina propria.5,6

Juvenile polyposis syndrome (JPS) is another autosomal dominant cancer syndrome marked by a germline mutation in SMAD4 or BMPR1A.1 JPS polyps are usually colorectal but can also occur in the stomach or small intestine. Colorectal JPS polyps are typically exophytic with smooth contours and cystically dilated glands filled with mucin. Surface erosion with edematous and inflamed lamina propria is frequently seen.1,6,7 Gastric JPS polyps are difficult to differentiate from gastric hyperplastic polyps and gastric PJ polyps solely based on histology. Of note, SMAD4 immunohistochemical stain may be of benefit, as approximately 50% of JPS polyps will show loss of staining.1

Intestinal-type adenoma with low-grade dysplasia is either a pedunculated or sessile polyp in the small intestine. Histologically, this polyp exhibits a tubular or tubulovillous growth pattern lined by intestinal-type epithelium, sometimes with a mixture of goblet cells, Paneth cells, or endocrine cells. Cytologically, the low-grade dysplastic epithelial cells, which is rare to see in PJ polyps, demonstrate polarized, enlarged, and elongated nuclei.1 Importantly, the characteristic arborizing smooth muscle and lobulated crypt architecture of PJ polyps are absent.4


  1. WHO Classification of Tumors Editorial Board. Digestive system tumors. Lyon (France): International Agency for Research on Cancer; 2019.
  2. Beggs AD, Latchford AR, Vasen HF, et al. Peutz-Jeghers syndrome: a systematic review and recommendations for management. Gut. 2010;59(7):975-986.
  3. Iwamuro M, Aoyama Y, Suzuki S, et al. Long-Term Outcome in Patients with a Solitary Peutz-Jeghers Polyp. Gastroenterology research and practice. 2019;2019:8159072.
  4. Tse JY, Wu S, Shinagare SA, et al. Peutz-Jeghers syndrome: a critical look at colonic Peutz-Jeghers polyps. Modern pathology : an official journal of the United States and Canadian Academy of Pathology, Inc. 2013;26(9):1235-1240.
  5. Borowsky J, Setia N, Rosty C, et al. Spectrum of gastrointestinal tract pathology in a multicenter cohort of 43 Cowden syndrome patients. Modern pathology : an official journal of the United States and Canadian Academy of Pathology, Inc. 2019;32(12):1814-1822.
  6. Shaco-Levy R, Jasperson KW, Martin K, et al. Morphologic characterization of hamartomatous gastrointestinal polyps in Cowden syndrome, Peutz-Jeghers syndrome, and juvenile polyposis syndrome. Human pathology. 2016;49:39-48.
  7. van Hattem WA, Langeveld D, de Leng WW, et al. Histologic variations in juvenile polyp phenotype correlate with genetic defect underlying juvenile polyposis. The American journal of surgical pathology. 2011;35(4):530-536.

Benjamin Van Treeck, M.D.

Gastrointestinal/Liver Pathology Fellow, Anatomic and Clinical Pathology
Mayo Clinic

Tsung-Teh Wu, M.D., Ph.D.

Consultant, Anatomic Pathology
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

A man was evaluated for alpha-1 antitrypsin (A1AT) deficiency (A1AD) after a history of abnormal liver function tests. The patient’s brother was previously diagnosed with A1AD with a ZZ phenotype and had a recent liver transplant. Other family history is unknown. The patient was originally phenotyped as MZ at an outside institution, but his A1AT levels were lower than expected for the MZ phenotype. Samples were sent for evaluation of an uncommon A1AT variant.

Currently, which of the following laboratory techniques would be most helpful for the evaluation of a rare A1AT variant?

  • Nephelometry
  • Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
  • Isoelectric Focusing (IEF) Gel Electrophoresis
  • Melt Curve Analysis by Real-time PCR

The correct answer is ...

The correct answer is: Isoelectric Focusing (IEF) Gel Electrophoresis.

Alpha-1 antitrypsin (A1AT) is a serine protease inhibitor encoded by the SERPINA1 gene on chromosome 14 and produced in hepatocytes. The main function of A1AT is to protect the lungs from neutrophil elastase, an enzyme that is produced by white blood cells for the purpose of degrading bacterial outer membranes. The wild-type allele (M) codes for functionally expressed A1AT protein, while certain single nucleotide polymorphisms (SNPs) can cause the resulting protein to be expressed at lower concentrations. The two most common alleles associated with A1AT deficiency are S and Z. In the context of deficiency, A1AT is not present in high enough concentrations to inhibit neutrophil elastase in the lungs, leading to degradation of elastin within the alveoli, resulting in loss of elasticity and structural integrity. In addition to losing protection against neutrophil elastase in the lungs, certain A1AT variants polymerize in hepatocytes, causing liver damage. Since A1AT alleles are inherited in an autosomal codominant pattern, which is referred to as a phenotype, people can have varying A1AT expression levels with homozygous MM being fully expressed and homozygous ZZ being the most deleterious and most frequently associated with clinical manifestations of deficiency. Determining a patient’s A1AT concentration and phenotype is important in determining what treatment is needed.

Quantitation by nephelometry is a technique used to determine the amount of circulating A1AT (1). It works by adding antibodies to A1AT to the patient’s sample, and measuring the scatter observed in the solution. This scatter is proportional to the concentration of A1AT, calculated by using a standard curve. While determining the amount of A1AT a patient has is important for their diagnosis of A1AD, this technique does not provide any information about the individual’s phenotype. 

Genotyping by melt curve analysis uses real-time PCR to determine if the patient has particular SNPs in exon 3 (S variant) or exon 5 (Z variant) of the SERPINA1 gene (2). The technique uses PCR to amplify a DNA fragment around each SNP and uses Förster resonance energy transfer (FRET) probes to determine the presence or absence of S or Z alleles. This technique does not give any information about the presence of other alleles and does not directly detect the wild-type M allele.

Proteotyping by liquid chromatography tandem mass spectrometry (LC-MS/MS) is a technique that can be used to identify the presence of A1AT S and Z variant proteins (3,4). Patient serum samples are digested with trypsin, and the resulting A1AT peptide fragments are separated by LC followed by MS/MS. Similar to genotyping, this technique does not specifically detect the M allele or other variant proteins.

Phenotyping by isoelectric focusing (IEF) gel electrophoresis separates out the distinct A1AT proteins in agarose gels by their isoelectric point (5). The proteins will migrate to the point on the gel at which it has no net charge. The protein variants are identified based on the distinct migration pattern when compared to the protein derived from the M allele. This technique can be used to detect the wild-type M allele, the common S and Z deficiency alleles, and rare variants, as each will show a distinct band on the IEF gel.


  1. Kanakoudi F, Drossou V, Tzimouli V, Diamanti E, Konstantinidis T, Germenis A, Kremenopoulos G. Serum concentrations of 10 acute-phase proteins in healthy term and preterm infants from birth to age 6 months. Clin Chem. 1995 Apr;41(4):605-8. PMID: 7536645.
  2. Lyon E. Mutation detection using fluorescent hybridization probes and melting curve analysis. Expert Rev Mol Diagn. 2001 May;1(1):92-101. doi: 10.1586/14737159.1.1.92. PMID: 11901805.
  3. Donato LJ, Karras RM, Katzmann JA, Murray DL, Snyder MR. Quantitation of circulating wild-type alpha-1-antitrypsin in heterozygous carriers of the S and Z deficiency alleles. Respir Res. 2015 Aug 5;16(1):96. doi: 10.1186/s12931-015-0256-9. PMID: 26243289; PMCID: PMC4531808.
  4. Chen Y, Snyder MR, Zhu Y, Tostrud LJ, Benson LM, Katzmann JA, Bergen HR 3rd. Simultaneous phenotyping and quantification of α-1-antitrypsin by liquid chromatography-tandem mass spectrometry. Clin Chem. 2011 Aug;57(8):1161-8. doi: 10.1373/clinchem.2011.163006. Epub 2011 Jun 2. PMID: 21636698; PMCID: PMC3275912.
  5. Donato LJ, Jenkins SM, Smith C, Katzmann JA, Snyder MR. Reference and interpretive ranges for α(1)-antitrypsin quantitation by phenotype in adult and pediatric populations. Am J Clin Pathol. 2012 Sep;138(3):398-405. doi: 10.1309/AJCPMEEJK32ACYFP. PMID: 22912357.
Photo of Nicholas E. Larkey, Ph.D.

Nicholas Larkey, Ph.D.

Fellow, Clinical Chemistry
Mayo Clinic

Melissa Snyder, Ph.D., DABCC

Division Chair, Clinical Biochemistry
Mayo Clinic
Associate Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

A 68-year-old man presented for evaluation of bilateral gynecomastia. The patient was not prescribed any medications known to cause gynecomastia, denied steroid use, and was not taking over-the-counter vitamins. Laboratory testing revealed an elevated serum concentration of β-human chorionic gonadotropin (β-hCG) (Table). The clinician contacted the laboratory to investigate whether the β-hCG test could have been affected by analytical interference. Interference studies were performed, including measuring β-hCG on an alternate platform and sample pre-treatment with a heterophile blocker (Table).

Table 1

What is the most likely explanation for the elevated β-hCG result in this patient?

  1. Cross-reactivity of luteinizing hormone with the β-hCG assay
  2. Heterophile interference
  3. Hypogonadotropic (secondary) hypogonadism
  4. Hypergonadotropic (primary) hypogonadism

The correct answer is ...

The correct answer is: Hypergonadotropic (primary) hypogonadism.

Human chorionic gonadotropin (hCG) is a 36-kDa glycoprotein that is made up of two noncovalently-bound subunits (α and β). The α subunit structure found in hCG is also present in luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). hCG, LH, FSH, and TSH each have a unique β subunit, however, there is a high degree of similarity between the β subunits of hCG and LH [1]. Older generations of hCG assays were prone to cross-reactivity with LH, leading to occasional false increases in the measured concentration of hCG [2]. To minimize any cross-reactivity with other hormones and improve the specificity of hCG measurement, current immunoassays utilize monoclonal antibodies that recognize different sites on the hCG molecule and/or different forms of hCG (i.e., “nicked” hCG, β-core fragment, free β subunit). Therefore, cross-reactivity of LH would not be responsible for the elevated hCG observed in this patient.

hCG immunoassays are susceptible to other types of interference that can result in inaccurate measurements. The presence of endogenous antibodies called heterophile antibodies is a well-known interference that typically leads to increased results with immunoassays. Heterophile antibodies can react with assay reagents, leading to signal detection in the absence of analyte. When heterophile interference is suspected, several strategies can be used to investigate, such as measuring the sample at various dilutions, using an alternate methodology or test kit (with different reagents/antibodies), or pre-treating the sample with a heterophile blocking agent. Although not performed in this investigation, HCG in urine also can be measured to help determine whether an elevated serum elevation is true. Heterophile antibodies are not found in urine, therefore a negative urine HCG with an elevated serum HCG would suggest the serum result is a false positive. In this patient’s case, the β-hCG result was unchanged after treatment with a heterophile blocker. Furthermore, assaying the sample with a different method still showed an elevated value. Therefore, the findings from the laboratory’s work-up suggested that a heterophile antibody was not present in this sample.

After ruling out potential analytical interferences, physiological causes of increased β-hCG were considered, including hypogonadism. In hypogonadotropic (secondary) hypogonadism, there is a disruption in the hypothalamic-pituitary-gonadal axis that leads to low concentrations of gonadotropins (mainly LH and FSH) and testosterone [3]. Secondary hypogonadism is an unlikely diagnosis in this case, as the patient had high levels of LH and FSH. In hypergonadotropic (primary) hypogonadism, decreased production of testosterone results in upregulated LH and FSH secretion from the pituitary. Large increases in FSH and LH, as seen in this case, are suggestive of primary hypogonadism even with slight decreases in testosterone [4]. In patients with primary hypogonadism, increased transcription of LH can result in “leaky” transcription of hCG from the pituitary [5]. Pituitary secretion of hCG is often associated with concentrations in the range of 3 to 5 IU/L [6,7], and in some cases, can reach levels as high as 25-30 IU/L [8,9].


  1. Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics, 8th edition. Chapter 44: Pregnancy and Prenatal Testing. 2020
  2. Braunstein GD. False-positive serum human chorionic gonadotropin results: Causes, characteristics, and recognition. AJOG Reviews. 2002;187(1):217-224.
  3. Belchetz PE, Barth JH, Kaufman JM. Biochemical endocrinology of the hypogonadal male. Ann Clin Biochem 2010;47:503–15.
  4. Contemporary Practice in Clinical Chemistry, 4th Edition. Chapter 38: Laboratory Testing in Pregnancy and Reproductive Disorders. 2020
  5. Santen R, Hasan F, Thoren K, Farooki A. Pituitary as a Source of HCG: Residual Levels After Bilateral Testicular Tumor Removal. J Investig Med High Impact Case Rep. 2019;7:2324709619841414. doi:10.1177/2324709619841414
  6. Yoshimura K, Nakashima Y, Sugiyama K, Kohei N, Takizawa A. Supposed pituitary-production of human chorionic Gonadotropin induced by androgen deprivation therapy. Int Braz J Urol. 2019 Jan-Feb;45(1):38-44. 
  7. Snyder JA, Haymond S, Parvin CA, Gronowski AM, Grenache DG. Diagnostic considerations in the measurement of human chorionic gonadotropin in aging women. Clin Chem. 2005 Oct;51(10):1830-5.
  8. Cole LA, Khanlian SA, Muller CY. Detection of perimenopause or postmenopause human chorionic gonadotropin: an unnecessary source of alarm. Am J Obstet Gynecol. 2008 Mar;198(3):275.e1-7.
  9. Cole LA, Sasaki Y, Muller CY. Normal production of human chorionic gonadotropin in menopause. N Engl J Med 2007;356:1184-1186.
Photo of Erica Fatica, Ph.D

Erica Fatica, Ph.D.

Fellow, Clinical Chemisty
Mayo Clinic

Alicia Algeciras-Schimnich

Alicia Algeciras-Schimnich, Ph.D.

Consultant, Clinical Biochemistry
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

You are the clinical lab director at your regional Accountable Care Organization and have noticed that 25-OH vitamin D testing has risen more than 50% year-over-year across the organization. Further evaluation reveals that the majority of tests are being ordered for routine screening purposes. 

What would be the most appropriate recommendation for your organization given these observed trends?

  • No changes needed; there is a clinical indication for testing
  • Implement a Clinical Decision Support tool for vitamin D testing within the electronic health record as part of a Quality Improvement initiative
  • Restrict ordering of the test to Endocrinology providers only
  • Conduct a prospective multisite cost/benefit evaluation of outcomes of patients undergoing vitamin D screening
  • None of the above

The correct answer is ...

The correct answer is: Implement a Clinical Decision Support tool for vitamin D testing within the electronic health record as part of a Quality Improvement initiative.

Utilization of 25-OH vitamin D testing as part of screening for Vitamin D deficiency in patients has rapidly increased in clinical practice, despite not much evidence demonstrating any associated benefits with measurement and supplementation. In 2014, $323 million was spent on Vitamin D level testing in Medicare patients alone. In 2013, as part of the ABIM Choosing Wisely campaign, the American Society for Clinical Pathology recommended against performing population-based screening for Vitamin D deficiency. As more health care organizations shift towards quality-based care, increasing emphasis is being placed on limiting unnecessary spending and resource utilization that do not lead to better patient outcomes.

Clinical Decision Support (CDS) tools, typically integrated within the electronic health record, have been demonstrated to reduce rates of unnecessary orders and procedures and subsequently improve quality of clinical care. Types of CDS include pop-up alerts, order sets, infobuttons, documentation templates, and other clinical workflow tools. Additional advantages of CDS tools are that they can deliver actionable insights and expedite incorporation of new knowledge at the point of care. Potential pitfalls for CDS tools that are not properly implemented include provider alert fatigue and significant disruption to clinician workflows.

The third answer choice above is incorrect, as there are indications for Vitamin D testing that can, and should, be initiated in settings outside of the Endocrine subspecialty (i.e., workup for individuals with abnormal blood calcium levels, malabsorption syndromes, and chronic kidney disease, to name a few). The first and fourth answer choices are incorrect, as there have been multiple clinical trials that have not shown benefit of population-wide screening of Vitamin D and subsequent supplementation (e.g. cancer, Type 2 diabetes, depression, osteoarthritis, etc.).


  1. Choosing Wisely. American Society for Clinical Pathology. February 21, 2013. http://www.choosingwisely.org/clinician-lists/american-society-clinical-pathology-population-based-screening-for-vitamin-d-deficiency/. Accessed June 15, 2021.
  2. Felcher AH, Gold R, Mosen DM, Stoneburner AB. Decrease in unnecessary vitamin D testing using clinical decision support tools: making it harder to do the wrong thing. J Am Med Inform Assoc. 2017;24(4):776-780. doi:10.1093/jamia/ocw182
  3. LeFevre ML, LeFevre NM. Vitamin D Screening and Supplementation in Community-Dwelling Adults: Common Questions and Answers. Am Fam Physician. 2018 Feb 15;97(4):254-260. PMID: 29671532.
  4. Sattar N, Welsh P, Panarelli M, Forouhi NG. Increasing requests for vitamin D measurement: costly, confusing, and without credibility. Lancet. 2012;379(9811):95-96. doi:10.1016/S0140-6736(11)61816-3
  5. Tcheng, J. E., S. Bakken, D. W. Bates, H. Bonner III, T. K. Gandhi, M. Josephs, K. Kawamoto, E. A. Lomotan, E. Mackay, B. Middleton, J. M. Teich, S. Weingarten, and M. Hamilton Lopez, editors. 2017. Optimizing Strategies for Clinical Decision Support: Summary of a Meeting Series. Washington, DC: National Academy of Medicine

Ray Qian, M.D.

Fellow, Clinical Informatics
Mayo Clinic

Thomas Flotte, M.D.

Consultant, Anatomic Pathology
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

A 60-year old veterinarian presented with 4-week history of multiple nodular lesions on the left hand (Image 1). He had no history of travel, gardening, or any immunocompromising condition. He owned a Koi pond and recalled sustaining minor injuries from the spruce needs occasionally while cleaning the pond. Patient underwent biopsy and cultures were obtained. Mycobacterial cultures incubated at 30 degrees Celsius grew yellow pigmented colonies on exposure to light after 14 days of incubation (Image 2). No growth was seen at 37 degrees Celsius. Ziehl-Nielson stain was positive for acid-fast bacillus (Image 3). QuantiFERON was performed and was weakly positive as well. 

Image 1: Nodular lesions on dorsal left hand
Image 2: Yellow colonies on Middlebrook 7H10 media
Image 3: Ziehl-Nielson stain showing acid fast bacilli

Which of the following is the most likely organism identified in this case?

  • Mycobacterium marinum
  • Mycobacterium tuberculosis
  • Mycobacterium leprae
  • Mycobacterium kansasii

The correct answer is ...

The correct answer is: Mycobacterium marinum.

The history of injuries related to koi ponds, preferable growth at 30 degrees Celsius, yellow pigmentation on exposure to light and weakly positive QuantiFERON makes Mycobacterium marinum the most likely underlying pathogen in this case. Even though infection with M. tuberculosis typically results in a positive QuantiFERON, the clinical presentation and growth characteristics are not typical of M. tuberculosis. Growth of M. tuberculosis is typically seen at 37 degrees Celsius with dry, rough non-chromogenic colonies. M. leprae can cause cutaneous findings; however, it cannot be grown in the routine culture media. M. kansasii also produces yellow pigmentation on exposure to light and can cause false positive QuantiFERON; however, growth is preferably seen at 37 degrees Celsius rather than at 30 degrees Celsius, and pulmonary disease is most commonly seen.

M. marinum was first isolated from fish in 1926 and was recognized as a human pathogen in 1951 (1). Infection with M. marinum is relatively uncommon. It is also known as fish tank granuloma and typical exposure leading to infection includes aquarium-related fish or shellfish injuries. Diagnosis requires a high degree of clinical suspicion. AFB smear may be negative in more than two-thirds of patients and hence does not rule out infection, and cultures remain the gold standard for diagnosis (2). It takes about 1-2 weeks to grow in the culture media with optimal growth temperature of 28-32 degrees Celsius, and rare-to-no-growth at 37 degrees Celsius. Colonies produce a yellow pigment after exposure to light (photochromogen).

M. marinum can cause false positive QuantiFERON test. QuantiFERON test is based on the production of interferon gamma in response to early secretory antigen-6 (ESAT-6) and culture filtrate protein (CFP-10) of M. tuberculosis. ESAT-6 and CFP-1 are also found in M. marinum, which may result in false positive QuantiFERON. Other non-tuberculous mycobacteria that may cause false positive QuantiFERON include M. kansasii and M. szulgai.

The treatment for M. marinum is not well defined and is based on case reports. Usually it is susceptible to rifampin, ethambutol, clarithromycin, trimethoprim-sulfamethoxazole, and doxycycline. Isolates are usually resistant to isoniazid and pyrazinamide. General approach is to treat with at least two agents for 4-8 weeks after the resolution of symptoms, with total treatment duration of about 3-4 months (3).


  1. Nordén A, Linell F.1951. A new type of pathogenic mycobacterium. Nature. 168:826.
  2. Castillo NE, Gurram P, Sohail MR, Fida M, Abu Saleh O. Fishing for a Diagnosis, the Impact of Delayed Diagnosis on the Course of Mycobacterium marinum Infection: 21 Years of Experience at a Tertiary Care Hospital. Open Forum Infect Dis. 2020 Jan 4;7(1):ofz550. doi: 10.1093/ofid/ofz550. PMID: 31988976; PMCID: PMC6975249.
  3. Griffith, D. E., et al. (2007). "An official ATS/IDSA statement: diagnosis, treatment, and prevention of nontuberculous mycobacterial diseases." Am J Respir Crit Care Med 175(4): 367-416.

Madiha Fida, M.B.B.S.

Fellow, Clinical Microbiology
Mayo Clinic

Nancy Wengenack, Ph.D.

Consultant, Clinical Microbiology
Mayo Clinic
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

MCL Education

This post was developed by our Education and Technical Publications Team.