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| Web: | mayocliniclabs.com |
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| Email: | mcl@mayo.edu |
| Telephone: | 800-533-1710 |
| International: | +1 855-379-3115 |
| Values are valid only on day of printing | |
A 49-year-old female with FLT3+ AML became refractory to platelet transfusions 2 weeks after initiating chemotherapy with venetoclax, midostaurin, and corticosteroids. A solid phase single antigen bead (SAB) assay demonstrated the patient had an antibody to all HLA-B antigens sharing the Bw6 epitope. Subsequently, she was given IVIG to help bolster her platelet counts. A solid phase red blood cell adherence platelet crossmatch was performed and a unit homozygous for Bw4 class antigens was unexpectedly incompatible (image; right columns of wells). Repeat testing performed on a prior sample showed the unit was compatible (image; left columns of wells).
The correct answer is...
The correct answer is Assay interference by IVIG.
IVIG is manufactured by pooling plasma from a large number of donors, some of which can have HLA antibodies. The IVIG present in a patient’s sample can bind to the HLA antigens on the platelets utilized in a platelet crossmatch creating a positive (incompatible) result. Thus, the binding of HLA antibodies contained within the IVIG can cause an erroneously false positive crossmatch result. The other agents/drugs do not cause interference with the platelet crossmatch assay.
References
1. Immucor Capture-P® Solid Phase System for the Detection of IgG Antibodies to
Platelets package insert; version 340-14.
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Holly Berg, D.O. Resident, Anatomic and Clinical Pathology Mayo Clinic @DOPathGal |
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Justin Juskewitch, M.D., Ph.D. Senior Associate Consultant, Transfusion Medicine Mayo Clinic Assistant Professor of Laboratory Medicine and Pathology Mayo Clinic College of Medicine and Science |
A 17 year old boy presented with symptoms consistent with motor neuron disease. He has no known family history of neuromuscular disease. Molecular analysis from an outside institution reported 2 copies of SMN1, 2 copies of SMN2, and a homozygous point mutation. However it could not be determined whether this mutation was in the SMN1 or SMN2 gene. Importantly, microarray analysis revealed consanguinity. SMN1 full gene analysis revealed a homozygous pathogenic mutation in exon 6 (c.683T>A).
The correct answer is...
The correct answer is Spinal Muscular Atrophy, Familial Mutation Targeted Testing.
Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disease which occurs in one out of every 10,000 live births, making it the leading genetic cause of infant mortality. SMA is characterized by degeneration of the alpha motor neurons of the spinal cord leading to progressive muscle weakness, and in cases of Type I SMA, progression to respiratory failure and death before the age of two if supportive therapies are not initiated.
However, SMA is a clinically heterogeneous disease, with Type I being the most severe of the four types. Patients with Type II SMA present with marked delay in gross motor development by 6-18 months of life, never become ambulatory, and suffer from progressive weakness, scoliosis, and restrictive lung disease. Life expectancy of SMA Type II patients ranges from two years of age to 40 years of age. Patients with Type III SMA have variable age of onset and clinical course. They often require wheelchair assistance by adolescence; however their life expectancy does not significantly differ from the general population. The mildest type of SMA, Type IV, generally presents in the second or third decade of life with mild proximal limb girdle weakness that progresses slowly.
All four types of SMA are caused by a mutation or deletion in the survival motor neuron 1 (SMN1) gene. Humans also have the survival motor neuron 2 (SMN2) gene, which differs from SMN1 gene by five nucleotides. All of these nucleotides are in non-coding regions, except for the cysteine to thymine variation in exon 7. Ultimately, this variation is translationally silent and the amino acid sequence of SMN2 is identical to SMN1; however the variation affects the alternative splicing such that 90% of transcripts are missing exon 7 and result in an unstable protein that is rapidly degraded. Accordingly, there is an inverse relationship between SMN2 copy number and disease severity. In general, type I SMA patients have two copies of SMN2, type II SMA patients have three copies of SMN2, and type III SMA patients have three or four copies of SMN2.
Molecular analysis of SMA patients has become increasingly important as there are now two new therapies that have recently been FDA-approved for the treatment of SMA. In December of 2016, Spinraza was FDA-approved to treat all types of SMA. Spinraza is an antisense oligonucleotide that binds downstream of exon 7 promoting the inclusion of exon 7, thereby increasing the amount of full-length SMN2 mRNA and, subsequently, increasing the level of full-length SMN protein. In May 2019, the FDA approved the use of Zolgensma for the treatment of SMA patients under the age of two. Zolgensma is gene replacement therapy using the AAV9 viral vector to replace the SMN1 gene. Molecular diagnosis of SMA is imperative to be able to initiate therapy in a timely manner as to maximize the protection of motor function in these patients.
The SMN1 gene exon 7 is homozygously absent in approximately 95% of affected patients. The great majority of the remainder of SMA cases is heterozygous for the exon 7 deletion and a small more subtle mutation in the other allele; compound heterozygotes. SMA cases resulting from homozygous point mutations are exceedingly rare. Therefore, the first line molecular analysis for the diagnosis of SMA consists of detecting the homozygous loss of exon 7 of the SMN1 gene. This can be done using techniques such as MLPA, qPCR, or ddPCR, which typically detect the presence of exon 7 of the SMN1 gene, thereby quantifying the number of copies of the SMN1 gene. If the result from these techniques is inconclusive or negative, it is recommended to perform full gene analysis of the SMN1 gene, typically via long-range-PCR of SMN1 exons 2-8, followed by bidirectional Sanger sequence analysis. Lastly, if the results from SMN1 full gene analysis is negative, a neuromuscular genetic panel analysis, typically via next-generation sequencing (NGS) and/or Sanger sequencing, could be considered.
In cases in which one or more variants have been identified in the patient or a family member, familial targeted testing (FMTT) can be considered. In this case, the patient was reported to have a known pathogenic variant. Furthermore, it was reported that consanguinity was determined via microarray analysis. While FMTT was not needed to make the SMA diagnosis for this patient, it could have been utilized to make the diagnosis in the patient by targeting this variant as well as determining that each parent was heterozygous for the same variant.
SMN2 full gene analysis is not needed to make the diagnosis of SMA. However, of note, there are known sequence variants of SMN2 that have been shown to be modulators of SMA disease severity. The variant c.859G>C in SMN2 exon 7 creates a new splice enhancer-binding site which in turn increases the exon 7 inclusion. This variant is correlated with a milder SMA phenotype. The A-44G variant in the SMN2 gene is another positive disease modifier. This variant was shown to decrease RNA-binding protein HuR and increase exon 7 inclusion. This variant is also associated with a milder clinical phenotype. Recently, a large study of 217 SMA patients in which the SMN2 gene was fully sequenced, it was determined that the variants A-44G, A-549G, and C-1897T in intron 6 of SMN2 were significantly associated with a clinical presentation that was discordant SMN2 copy number. Therefore, SMN2 full gene analysis may be insightful in SMA patients that have a clinical presentation that is discordant with their SMN2 copy number.
References
1. Burghes, A., Beattie, C. Spinal muscular atrophy: why do low levels of survival motor neuron protein make motor neurons sick? Nat Rev Neurosci 2009; 10, 597–609.
2. Bürglen L, Lefebvre S, Clermont O, et al. Structure and organization of the human survival motor neurone (SMN) gene. Genomics. 1996;32(3):479-482.
3. Clermont O, Burlet P, Benit P, et al: Molecular analysis of SMA patients without homozygous SMN1 deletions using a new strategy for identification of SMN1 subtle mutations. Hum Mutat 2004; 24:417-427.
4. Faravelli I, Nizzardo M, Comi GP, Corti S. Spinal muscular atrophy--recent therapeutic advances for an old challenge. Nat Rev Neurol. 2015; 11(6):351-9.
5. Feldkötter M, Schwarzer V, Wirth R, Wienker TF, Wirth B. Quantitative analyses of SMN1 and SMN2 based on real-time lightCycler PCR: fast and highly reliable carrier testing and prediction of severity of spinal muscular atrophy. Am J Hum Genet. 2002; 70(2):358-368.
6. Kubo Y, Nishio H, Saito K: A new method for SMN1 and hybrid SMN gene analysis in spinal muscular atrophy using long-range PCR followed by sequencing. J Hum Genet 2015; 60: 233-239.
7. Lefebvre S, Bürglen L, Reboullet S, et al. Identification and characterization of a spinal muscular atrophy-determining gene. Cell. 1995; 80(1):155-165.
8. Mahajan R. Onasemnogene Abeparvovec for Spinal Muscular Atrophy: The Costlier Drug Ever. Int J Appl Basic Med Res. 2019; 9(3):127-128.
9. Pearn J. Incidence, prevalence, and gene frequency studies of chronic childhood spinal muscular atrophy. J Med Genet. 1978; 15(6):409-13.
10. Prior TW. Carrier screening for spinal muscular atrophy. Genet Med 2008;10:840-2.
11. Prior T, Finanger E: Spinal Muscular Atrophy. Gene Reviews. Update Dec 22, 2016.
12. Prior TW, Krainer AR, Hua Y, et al. A positive modifier of spinal muscular atrophy in the SMN2 gene. Am J Hum Genet. 2009; 85(3):408-413.
13. Ruhno C, McGovern VL, Avenarius MR, et al. Complete sequencing of the SMN2 gene in SMA patients detects SMN gene deletion junctions and variants in SMN2 that modify the SMA phenotype. Hum Genet. 2019; 138(3):241-256.
14. Shorrock, H.K., Gillingwater, T.H. & Groen, E.J.N. Overview of Current Drugs and Molecules in Development for Spinal Muscular Atrophy Therapy. Drugs 2018; 78, 293–305.
15. Sugarman EA, Nagan N, Zhu H, Akmaev VR, Zhou Z, Rohlfs EM, Flynn K, Hendrickson BC, Scholl T, Sirko-Osadsa DA, Allitto BA. Pan-ethnic carrier screening and prenatal diagnosis for spinal muscular atrophy: clinical laboratory analysis of >72,400 specimens. Eur J Hum Genet. 2012; 20(1):27-32.
16. Vidal-Folch N, Gavrilov D, Raymond K, Rinaldo P, Tortorelli S, Matern D, Oglesbee D. Multiplex Droplet Digital PCR Method Applicable to Newborn Screening, Carrier Status, and Assessment of Spinal Muscular Atrophy. Clin Chem. 2018; 64(12):1753-1761.
17. Wirth B: An update of the mutation spectrum of the survival motor neuron gene (SMN1) in autosomal recessive spinal muscular atrophy (SMA). Hum Mutat 2000; 15:228-237.
18. Wu X, Wang SH, Sun J, Krainer AR, Hua Y, Prior TW. A-44G transition in SMN2 intron 6 protects patients with spinal muscular atrophy. Hum Mol Genet. 2017; 26(14):2768-2780.
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Sara Cook, M.D., Ph.D. Resident, Anatomic and Clinical Pathology Mayo Clinic |
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Ross Rowsey, Ph.D. Senior Associate Consultant, Laboratory Genetics and Genomics Mayo Clinic Assistant Professor of Laboratory Medicine and Pathology Mayo Clinic College of Medicine and Science |
A 46 year old male presented to an express care clinic with a 1-day history of fever, headache, chills, abdominal pain, nausea, and vomiting. He had returned 10 days prior to presentation from a 9 month trip to Ethiopia. To evaluate the patient for malaria, microscopic examination of Giemsa-stained thick and thin peripheral blood smears was performed, and the organisms shown in Images 1 and 2 were identified.
The correct answer is...
The correct answer is Plasmodium vivax.
Plasmodium vivax is the most widely distributed of all of the species causing human malaria, being found in areas of the tropics and subtropics worldwide, as well as some temperate climates. The regions with highest prevalence are Latin America and Southeast Asia. While majority (60-70%) of malaria cases in Ethiopia are contributed to Plasmodium falciparum, the remaining 30-40% of infections is caused by P. vivax, and infections due to Plasmodium ovale and Plasmodium malariae are rare (1). Plasmodium knowlesi is endemic to Southeast Asia and does not fit this case due to travel history. P. vivax has a low degree of infectivity compared to P. falciparum, which can rapidly progress to life-threatening disease. While all malaria species have an initial liver stage, only P. vivax and P. ovale have a dormant liver stage, where hypnozoites can persist in the liver and cause relapses by invasion into the blood stream weeks to months after initial infection is cleared (2).
The various Plasmodium species can be differentiated based on their appearance on Giemsa and Wright-Giemsa stained thin blood films. P. vivax and P. ovale preferentially infect immature red blood cells (RBCs), and thus the infected cells are larger than many of the surrounding uninfected cells. Intracytoplasmic inclusions (i.e., Schüffner’s stippling or ‘dots’) are also characteristic when the stain is at a neutral pH (7.0 – 7.2). In comparison, the size of the infected RBCs is usually normal or small in P. falciparum and P. malariae infections, and Schüffner’s dots are not seen. Differentiating P. vivax from P. ovale can be more challenging. In general, P. vivax late stage trophozoites have an ameboid shape (i.e., having pseudopod-like projections) whereas P. ovale late stage trophozoites are more compact. Additionally, P. vivax infected RBCs exhibit increased flexibility, causing them to mold to the countours of the neighboring cells. This is not seen in P. ovale infected red blood cells, which instead take on an overall ovoid shape (in approximately 1/3 of infected RBCs) and may have jagged (i.e., fimbriated) edges. Characteristic features of P. vivax can be seen in both of the images in this case. In Image 1, a late-stage trophozoite (arrow) has an ameboid shape, and both infected RBCs are partially molded to neighboring cells. In the second image, stippling can be seen in the gametocyte, and the parasite fills nearly the entire RBC. The infected cell is also partially molded to the neighboring RBC.
References
1. https://wwwnc.cdc.gov/travel/yellowbook/2020/preparing-international-travelers/yellow-fever-vaccine-and-malaria-prophylaxis-information-by-country/ethiopia#5407
2. https://www.cdc.gov/dpdx/malaria/index.html
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Allison Eberly, Ph.D. Fellow, Clinical Microbiology Mayo Clinic @ali_eberly |
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Bobbi Pritt, M.D. Division Chair, Clinical Microbiology Mayo Clinic Professor of Laboratory Medicine and Pathology Mayo Clinic College of Medicine and Science @ParasiteGal |
A 62-year-old male with chronic kidney disease presented for a kidney transplant evaluation. The patient had a history of coronary artery disease, hypertension, and secondary hyperparathyroidism for which he underwent a total parathyroidectomy with autotransplantation 16 years prior. He takes furosemide, metoprolol, and a multivitamin. Laboratory testing using a sandwich immunoassay revealed a parathyroid hormone (PTH) concentration of >4100 pg/mL. The provider called the lab to investigate this unexpectedly high value. Laboratory results are shown in the Table.
| Serum Analytes | Reference Interval | Jan | Feb | March | April |
| PTH | 15 - 65 pg/mL | 835 | 897 | 795 | >4100 |
| Calcium, total | 8.8 - 10.2 mg/dL | 8.3 | 7.8 | 8.6 | 8.5 |
| Creatinine | 0.74 - 1.35 mg/dL | 7.7 | 7.3 | 12.4 | 10.8 |
| Phosphorus | 2.5 - 4.5 mg/dL | 3.8 | 4.5 | 7.0 | 6.5 |
| Magnesium | 1.7 - 2.3 mg/dL | 1.8 | 1.6 | 1.7 | 1.8 |
The correct answer is...
The correct answer is Variation in blood draw site.
The function of parathyroid hormone (PTH) is to regulate the concentration of calcium and phosphorus in the blood by acting upon several target organs. PTH increases the release of calcium and phosphorus from the bones and increases calcium reabsorption while promoting phosphorous excretion from the kidneys. PTH also stimulates the production of the active form of vitamin D (1,25-dihydroxyvitamin D) in the kidneys, which increases absorption of calcium and phosphorus from the intestine (1).
Pathophysiological increases in parathyroid hormone are associated with hyperparathyroidism, which can be classified as primary, secondary, or tertiary. Secondary hyperparathyroidism most commonly occurs as a result of renal failure or vitamin D deficiency but can also occur in malabsorption syndromes (i.e. Crohn’s disease, celiac disease), pseudohyperparathyroidism, or with the use of certain medications (i.e. bisphosphonates, anticonvulsants) (2). Secondary hyperparathyroidism of renal origin proceeds by two main mechanisms. First, impaired glomerular filtration leads to decreased renal excretion of phosphate and subsequent hypocalcemia. Second, individuals with renal disease produce less 1,25-vitamin D, causing a decrease in calcium absorption from the intestine. Hypocalcemia stimulates the parathyroid gland to release more PTH, manifesting as hyperparathyroidism (3).
Physiological explanations for the spuriously elevated PTH result for this patient are unlikely. This patient has a longstanding history of secondary hyperparathyroidism of renal origin. Although his high serum creatinine concentrations do show a gradual decline in kidney function, his serum creatinine was higher a month prior than at the time of the questionable PTH result. Moreover, aside from PTH, all other laboratory results between the last two draws are consistent. If the PTH concentration had truly increased by more than four times the previous result, one would expect to see marked aberrations in other analytes as well. The second most common cause of secondary hyperparathyroidism, vitamin D deficiency, can also be ruled out. Vitamin D deficiency presents with high PTH, low serum calcium, and low or normal levels of phosphorus. At the time of the questionable PTH result, the patient had hyperphosphatemia.
After eliminating physiological explanations, pre-analytical or analytical reasons need to be considered. Analytical interference due to prescription and over-the-counter medications or supplements such as biotin can cause erroneous results in immunoassays that use biotinylated antibodies to capture analytes of interest, including assays for PTH (4,5). The direction of interference depends on the assay format. Competitive immunoassays may have falsely elevated results while non-competitive sandwich immunoassays will have falsely decreased results (6). There are several strategies to investigate biotin interference, including dilution studies or rerunning the sample on an alternate platform. To prevent biotin interference, patients should avoid taking supplements with biotin before sample collection. In this case, the questionable PTH result was measured using a sandwich immunoassay. The result in question was markedly increased compared to previous results, so biotin interference can be ruled out.
There are a number of pre-analytical factors that can influence a laboratory result. Fasting state, diet, patient posture, prolonged tourniquet use, tube additives, order of draw, and collection technique including draw site are just a few such variables. In this case, none of these variables are expected to cause the magnitude of change observed for this patient. The key to this case is that the patient had undergone a parathyroidectomy 16 years prior to manage his secondary hyperparathyroidism. It is common during total parathyroidectomies for the surgeon to implant the parathyroid gland into the patient’s forearm, known as auto-transplantation (7). The sample in question was drawn from the patient’s right forearm where his parathyroid tissue was implanted, resulting in a significantly elevated PTH concentration of >4100 pg/mL.
References
1. Tietz Textbook of Clinical Chemistry
2. Yang, Lang & Arnold, A & Brandi, M & Brown, E & D'Amour, P & Hanley, David & Rao, Sudhaker & Rubin, M & Goltzman, David & Silverberg, Shonni & Marx, S & Peacock, Munro & Mosekilde, L & Bouillon, Roger & Lewiecki, E.. (2009). Diagnosis of Asymptomatic Primary Hyperparathyroidism: Proceedings of the Third International Workshop. The Journal of clinical endocrinology and metabolism. 94. 340-50. 10.1210/jc.2008-1758.
3. McPherson, Richard and Pincus, Matthew R., "Henry's Clinical Diagnosis and Management by Laboratory Methods" (2017). Faculty Bookshelf. 81.
https://hsrc.himmelfarb.gwu.edu/books/81
4. Waghray A, Milas M, Nyalakonda K, Siperstein AE. Falsely low parathyroid hormone secondary to biotin interference: a case series. Endocr Pract. 2013;19(3):451-455. doi:10.4158/EP12158.OR
5. Li D, Radulescu A, Shrestha RT, et al. Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults. JAMA. 2017;318(12):1150-1160.
6. Colon P, Greene D. Biotin Interference in Clinical Immunoassays. JALM. 2018;2(6):941-951.
7. Conzo G, Della Pietra C, Tartaglia E, et al. Long-term function of parathyroid subcutaneous autoimplantation after presumed total parathyroidectomy in the treatment of secondary hyperparathyroidism. A clinical retrospective study. Int J Surg. 2014;12 Suppl 1:S165-S169. doi:10.1016/j.ijsu.2014.05.019
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Erica Fatica, Ph.D. Resident, Clinical Chemistry Mayo Clinic |
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Darci Block, Ph.D. Consultant, Clinical Core Laboratory Services Mayo Clinic Assistant Professor of Laboratory Medicine and Pathology Mayo Clinic College of Medicine and Science |
A 66 year-old previously healthy man presented with hematuria and constitutional symptoms such as night sweats for over 2 years. CT scan of abdomen revealed retroperitoneal soft tissue thickening encasing the left ureter, abdominal aorta and central mesenteric vessels, concerning for IgG4 disease. Serum IgG4 was 50 mg/dL (reference: 2.4-121). Core needle biopsy of retroperitoneum was performed. Representative images are shown in Figure 1-3. Additional immunostains for CD1a and langerin were negative.
The correct answer is...
The correct answer is Erdheim-Chester disease.
Erdheim-Chester disease is a non-Langerhans cell histiocytosis and a clonal systemic process with multiorgan involvement and variable clinical outcomes.(1) Typical findings of ECD include central diabetes insipidus, perinephric fibrosis, and sclerotic bone lesions. The histopathologic diagnosis of ECD is often challenging due to nonspecific fibroinflammatory infiltrate.(2) Morphologically, in this case, the core biopsy shows a fibroadipose tissue involved by a subtle histiocytic infiltrate in a background of marked fibrosis, scattered lymphocytes and plasma cells (Figure 1). The histiocytes have oval to spindled nuclei and abundant amphophilic cytoplasm.The lesional histiocytes strongly express CD163, Factor 13a, BRAF V600E (Figure 2).
Rosai-Dorfman disease (RDD) is a non-Langerhans cell histiocytosis also known as sinus histiocytosis with massive lymphadenopathy. The classic sporadic RDD typically involves the lymph nodes, however, extranodal sites have been reported including skin, bone, nasal cavity, and soft tissue.(3) Morphologically, RDD is characterized by emperipolesis (engulfment of lymphocytes by large histiocytes) with expression of CD68, CD163, S100, and negative for CD1a and langerin.
IgG4 disease: The diagnosis of IgG4-related disease rests on the combined presence of the characteristic histopathological appearance, including dense lymphoplasmacytic infiltrate, a storiform pattern of fibrosis, and obliterative phlebitis and increased numbers of IgG4+ plasma cells (varies among affected organs, ranging from 10 to 200 cells/HPF).(4) In the above case, the core biopsy shows a focal plasma cell infiltrate and IgG4 plasma cells number up to 50 per HPF focally without an increase in IgG4+/IgG+ plasma cell ratio (Figure 3). These findings are not conclusive for IgG4 disease.
Reactive fibrosis: A reactive fibrosis with mixed inflammatory infiltrate, although in the differential, the strong expression of Factor 13a and BRAF V600E in the CD163-positive histiocytes supports a neoplastic process in the above case.
References
1. Swerdlow SH, Campo E, Harris NL, et al., eds. WHO Classification of Tumours of Hematopoietic and Lymphoid Tissues. Lyon, France: IARC; 2017.
2. Goyal G, Heaney ML, Collin M, et al., Erdheim-Chester disease: consensus recommendations for evaluation, diagnosism and treatment in the molecular era. Blood 2020; 135(22): 1929-1945.
3. Emile JF, Abla O, Fraitag S, Horne A, Haroche J, Donadieu J, et al. Revised classification of histiocytoses and neoplasms of the macrophage-dendritic cell lineages. Blood 2016 Jun 2; 127(22): 2672-2681.
4. Deshpande V, Zen Y, Chan JK, et al. Consensus statement on the pathology of IgG4-related disease. Mod Pathol. 2012;25(9):1181-1192.
 | Aishwarya Ravindran, M.B.B.S. Resident, Anatomic and Clinical Pathology Mayo Clinic @aravindranmd |
 | Karen Rech, M.D. Consultant, Hematopathology Mayo Clinic Associate Professor of Laboratory Medicine and Pathology Mayo Clinic College of Medicine and Science |
