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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_208_библиотеки_им_акад_М_И_Перельмана
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182 Laboratory Medicine in Psychiatry and Behavioral Science
Magnesium
Type of test Blood
Background and explanation
of test
Magnesium is a micronutrient required for the regulation of
blood pressure, muscle and nerve function, blood clotting,
carbohydrate metabolism, and protein and nucleic acid syn
-
thesis. Magnesium and calcium are functionally linked, with
magnesium required for calcium absorption by the intestine
and involved in calcium metabolism. With magnesium defi
-
ciency, calcium is removed from the bones and can cause cal-
cification of the aorta and kidney. In addition, a
low calcium
level may be difficult to correct unless low magnesium is also
corrected.
Under normal conditions, only about 1% of total body mag-
nesium is present in serum. Decreased renal function can be
associated with increased serum levels. Magnesium comes
from the diet, with levels in the body regulated by control of
excretion through the kidneys and absorption from the GI
tract. Abnormal levels may be seen when either of these con-
trols is compromised. When magnesium levels are low, po-
tassium levels are often also low.
Relevance to psychiatry and
behavioral science
Alcohol use disorder (AUD) and anorexia nervosa are both
associated with low magnesium levels, which can manifest
as agitation, delirium, or seizures. Lithium use, abuse of lax
-
atives, and overuse of antacids are associated with high mag-
nesium levels, which can manifest as a delirium of subacute
onset. Patients with depression who are deficient in magne
-
sium may show improvement in mood with magnesium
supplementation.
Preparation of patient Patients should fast for 4 hours before testing.
Indications •
Component of admission lab workup to evaluate electro-
lyte status
• Symptoms of abnormally low magnesium level, such as
muscle weakness, twitching, cramping, confusion, car
-
diac arrhythmia, or seizures
• Workup for malnutrition, diarrhea, or suspected mal-
absorption
•
Evaluating acute illness in patients with AUD
• Workup for patients with chronically low calcium and
potassium levels
Reference range Fasting serum levels
• <60 years: 1.6–2.6 mg/dL
•
60–90 years: 1.6–2.4 mg/dL
• >90 years: 1.7–2.3 mg/dL
Critical value(s) Hypomagnesemia: <1 mg/dL
Hypermagnesemia: >9
mg/dL
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183 Laboratory Tests
Magnesium (continued)
Increased levels • Oversupplementation or overuse of medications con-
taining magnesium, including antacids and laxatives
• Prolonged lithium or salicylate therapy
• Renal failure or insufficiency (acute or chronic)
• Low urine output
• Dehydration
• Hypothyroidism
• Addison’s disease or adrenalectomy
• Severe diabetic ketoacidosis
Decreased levels • Low dietary intake
• Malabsorption due to GI disorders (e.g., Crohn’s disease)
• Excessive body fluid loss (e.g., diuretic abuse, diarrhea)
• AUD with cirrhosis
• Chronic kidney disease
• Preeclampsia
• Uncontrolled diabetes, diabetic ketoacidosis
• Hemodialysis
• Tissue trauma (surgery or burns)
Interfering factors Sample hemolysis invalidates results.
Upright posture increases level by 4%.
Calcium gluconate and other drugs can falsely decrease
levels.
Levels are normally low in pregnancy after the first trimester.
Cross-references Alcohol Use Disorder
Anorexia Nervosa
Hypermagnesemia
Hypomagnesemia
American Association for Clinical Chemistry: Testing.com. Available at: https://www.testing.com. Ac-
cessed August 2021.
ARUP Laboratories: Critical Values List. Salt Lake City, UT, ARUP Laboratories, 2019. Available at:
https://www.aruplab.com/Testing-Information/resources/PDF_Brochures/ARUP_Critical_
Values.pdf. Accessed December 2021.
Fischbach FT, Fischbach MA: A Manual of Laboratory and Diagnostic Tests, 10th Edition. Philadelphia,
PA, Wolters Kluwer Health/Lippincott Williams and Wilkins, 2018
Li J, Hovey KM, Andrews CA, et al: Association of dietary magnesium intake with fatal coronary heart
disease and sudden cardiac death. J Womens Health (Larchmt) 29(1):7–12, 2020
Peeri NC, Egan KM, Chai W, Tao MH: Association of magnesium intake and vitamin D status with cog-
nitive function in older adults: an analysis of US National Health and Nutrition Examination Survey
(NHANES) 2011 to 2014.Eur J Nutr 60(1):465–474, 2021
Rajizadeh A, Mozaffari-Khosravi H, Yassini-Ardakani M, Dehghani A: Effect of magnesium supplemen-
tation on depression status in depressed patients with magnesium deficiency: a randomized, double-
blind, placebo-controlled trial. Nutrition 35:56–60, 2017
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184 Laboratory Medicine in Psychiatry and Behavioral Science
Magnesium (continued)
Reddy P, Edwards LR: Magnesium supplementation in vitamin D deficiency.Am J Ther 26(1):e124–e132,
2019
Tarleton EK, Littenberg B: Magnesium intake and depression in adults.J Am Board Fam Med 28(2):249–
256, 2015
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185 Laboratory Tests
Magnetic resonance imaging
Type of test Imaging
Background and explanation
of test
MRI uses a superconducting magnet and radiofrequency
signals to form high-resolution images of soft tissue, includ
-
ing white matter tracts, arteries, and lesions in the brain and
other CNS structures. The development of techniques over
the past few decades has made it possible to visualize tissue
architecture at a microscopic level, making MRI the tool of
choice in the investigation of stroke, white matter disease,
and other pathologies. Diffusion techniques have made it
possible to visualize the area of tissue ischemia in stroke be
-
fore that tissue has been infarcted, facilitating time-sensitive
interventions such as tissue plasminogen activator (tPA).
MRI studies usually include a series of pulse sequences such
as sagittal T1, axial T1, T2, diffusion-weighted, and FLAIR
images throughout the brain, without contrast. The contrast
agent gadolinium can be used to enhance visualization of
lesions such as stroke, tumor, or abscess. With contrast, se-
quences such as T1 spoiled gradient recalled echo and axial
T1 spin echo are used. In general, T1-weighted images are
used to identify anatomy, and T2-weighted images are used
to identify white matter disease. Brain MRI is superior to
head CT in the detection of ischemia and demyelination. It
is also better for viewing the brainstem and posterior fossa
structures. MRI is preferred to CT in identifying lesions rep
-
resenting seizure focus, nonmeningeal tumors, and vascular
malformations. On the other hand, MRI is about twice as
expensive as CT and is not universally available for clinical
use 24 hours a day.
For the MRI procedure, which takes about 45 minutes, pa-
tients are positioned supine on a flat table. During the test,
a loud tapping noise is heard that may be mitigated some
-
what by headphones. In a standard MRI, the patient’s head
and upper body are inside a narrow tube, and this can cause
problems for those who are claustrophobic. An open MRI is
available in which the sides of the tube do not obstruct the
view, so patients feel less confined. The open MRI is also
more suitable for obese patients. The problem with open
MRI is low magnet strengths; magnets used in clinical set-
tings range from 1.5 T to 3.0 T for closed systems and 0.2 T
to 0.35 T for open systems. In general, the stronger the mag
-
net, the better the image resolution. Research studies are
now done with extremely strong magnets of ≥7.0 T, and
7.0 T magnets have now been approved for clinical use in
the United States.
Relevance to psychiatry and
behavioral science
Characteristic MRI findings in schizophrenia include re-
duced total cerebral volume and atrophy of temporal
lobe(s); subcortical and limbic structures may or may not
show abnormalities. Characteristic MRI findings in affective
disorders include areas of high signal intensity in white
matter, volume loss in the prefrontal cortex, and alterations
in the subcortical and limbic structures.
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186 Laboratory Medicine in Psychiatry and Behavioral Science
Magnetic resonance imaging (continued)
Relevance to psychiatry and In ADHD, a 3%–4% reduction in total cerebral and cerebel-
behavioral science (continued) lar volumes, thinning of the medial prefrontal cortex, and
volume reduction in the dorsal anterior cingulate cortex are
characteristic. In autism spectrum disorder, gray matter ab
-
normalities have been found in the social brain network that
includes the amygdala and superior temporal sulcus.
Preparation of patient No pretest preparation is needed. Patients should be in-
formed that gadolinium contrast material can deposit itself
in the brain, mostly in the dentate nuclei and globus pal
-
lidus, and current recommendations are to use contrast
agents with caution. MRI should not be performed on pa
-
tients with implanted metal devices including pacemakers,
defibrillators, cochlear implants, metal heart valves, pumps,
neurostimulators, certain prostheses, and certain intrauter
-
ine devices. For surgical implants that are MRI compatible,
the brand, style, and serial number should be requested to
confirm compatibility. Guidelines for MRI in pregnancy
have been updated to reflect the safety of this modality, with
the understanding that gadolinium contrast should be used
only if it significantly improves diagnostic yield.
Indications (selected) • Evaluating for dementia
• Suspected NPH
• Suspected Huntington’s disease
• Suspected neurodegenerative disease with brain iron
accumulation
• Parkinsonian syndrome with atypical features
• New focal neurological deficit
• TIA involving carotid or vertebrobasilar arteries
• Ataxia, acute or slowly progressive
• Sudden-onset unilateral headache
• New headache: patients older than 60 years with sus-
pected temporal arteritis, patients with suspected men-
ingitis/encephalitis, HIV-positive patients, pregnant
patients
Normal test • Normal structures (pituitary gland and corpus callosum)
• No herniation of cerebellar tonsils
• No evidence of mass lesion, hemorrhage, or acute
ischemic injury
• No abnormality of gray or white matter on FLAIR
images
• No abnormal fluid collections or displacement of
midline structures
• No areas of abnormal enhancement with contrast
• Normal flow voids in major arteries
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187 Laboratory Tests
Magnetic resonance imaging (continued)
Normal test (continued) • Normal visualized portions of the paranasal sinus, or-
bits, and mastoids
• No abnormality of the calvarium
Abnormal test • Periventricular or subcortical white matter changes
(ischemia)
• Stroke, acute or old
• Hemorrhage
• Atrophy, focal or regional
• Generalized atrophy (graded as mild, moderate, or
severe)
• Ventricular dilatation (hydrocephalus)
• Vascular abnormalities (aneurysms, arteriovenous
malformations)
• Vasculitis
• Neoplasm, abscess, or other mass lesion
• Infectious disease: toxoplasmosis, tuberculosis, or
herpes encephalitis
Interfering factors Perivascular spaces (Virchow-Robin spaces) can be mis-
taken for lacunar infarcts. These spaces are filled with inter-
stitial fluid and are isointense with ventricles. Virchow-
Robin spaces appear as round, oval, or linear (depending on
plane of section) and are usually ≤ 5 mm, although they can
be larger. Usually, Virchow-Robin spaces are suppressed
completely on FLAIR images.
Cross-references Angiography, Magnetic Resonance (Cerebrovascular)
Computed Tomography Scan, Head
Neuroimaging Signal Appearance (Appendix B)
Agarwal N, Port JD, Bazzocchi M, et al: Update on the use of MR for assessment and diagnosis of psy-
chiatric diseases. Radiology 255:23–41, 2010
Gulani V, Calamante F, Shellock FG, et al: Gadolinium deposition in the brain: summary of evidence and
recommendations. Lancet Neurol 16(7):564–570, 2017
Le Bihan D: Diffusion MRI: what water tells us about the brain. EMBO Mol Med 6(5):569–573, 2014
Le Bihan D, Johansen-Berg H: Diffusion MRI at 25: exploring brain tissue structure and function. Neuro-
image 61(2):324–341, 2012
Mitelman SA: Transdiagnostic neuroimaging in psychiatry: a review. Psychiatry Res 277:23–38, 2019
https://t.me/med1917
188 Laboratory Medicine in Psychiatry and Behavioral Science
Magnetic resonance spectroscopy (MRS)
Type of test Neuroimaging
Background and explanation
of test
Brain MRS uses the same basic technology and scanning
equipment as MRI, with software programmed to acquire
data regarding tissue metabolite levels. Three methods in
common use include
1
H MRS,
31
P MRS, and
23
Na MRS.
1
H MRS is the fastest to perform and has the best signal-to-
noise ratio of the three. Results of scanning are reported as a
spectrum, with peaks representing signal intensities as a
function of frequency (expressed
as ppm). Data are obtained
either from one area of interest (single-voxel spectroscopy) or
from multiple regions (magnetic resonance spectroscopic
imaging).
With
1
H MRS, the following metabolites can be detected:
• Lipids—products of brain destruction at 0.9–1.4 ppm
• Lactate—product of anaerobic metabolism at 1.3 ppm
• N-acetylaspartate (NAA)—neuronal density at 2.0 ppm
•
Glutamine and GABA—neurotransmitters at 2.2–2.4 ppm
• Creatine—reflecting energy stores at 3.0 ppm
• Choline—marker of cellular turnover at 3.2 ppm
• Myoinositol—glial cell marker, osmolyte at 3.5 ppm
• Other detectable substances include ethanol, glucose,
mannitol, and alanine.
Other neurotransmitters (dopamine, serotonin, acetylcho-
line) are invisible to MRS, as are DNA, RNA, and most pro-
teins and enzymes.
Relevance to psychiatry and MRS can probe pathological processes occurring at the
behavioral science cellular level before morphological changes appear on
structural study. Unlike existing imaging modalities that
detect only coarse brain disease, MRS has the potential to
investigate chemical abnormalities underlying various
psychiatric disorders. In bipolar disorder,
1
H MRS shows
reduced NAA in the prefrontal cortex and hippocampus in
adults, adolescents, and at-risk patients. Alterations in the
myoinositol-to-creatine ratio generally parallel mood state,
with increased ratios in mania and euthymia and decreased
ratios in bipolar depression.
31
P MRS in bipolar disorder
shows altered phospholipid metabolism. Disorders such as
PTSD, OCD, and generalized anxiety disorder show reduced
NAA in the striatum and anterior cingulate cortex. The ratio
of NAA to creatine tends to be lower in subjects with mild
cognitive impairment who convert to dementia compared
with those who do not.
Preparation of patient See Magnetic Resonance Imaging. Use of
1
H MRS adds
~15 minutes to the MRI study.
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189 Laboratory Tests
Magnetic resonance spectroscopy (MRS) (continued)
Indications MRS is used clinically to investigate the following:
• Brain tumors
• Hypoxic/ischemic insults
• Cases of near drowning
• TBI
• Brain infections, such as abscess
• Demyelinating disorders
Clinical use is emerging for application of MRS to neurode-
generative diseases, stroke, and epilepsy.
Normal result Principal metabolite peaks are those of NAA, creatine, cho-
line, and myoinositol.
Normal ratios
• NAA-to-creatine: 2.0
• NAA-to-choline: 1.6
• Choline-to-creatine: 1.2
Abnormal result Examples of abnormal findings:
• With malignancy, NAA and creatine decrease and cho-
line, lactate, and lipids increase.
• Marked elevation of lactate is consistent with ischemia.
• Increase in lipids occurs with stroke.
• In AIDS dementia, NAA is reduced and choline elevated.
• In hepatic encephalopathy, marked reduction in myoino-
sitol is seen, along with reduced choline and increased
glutamine.
• In advanced Alzheimer’s disease, NAA is reduced and
myoinositol elevated. Myoinositol elevation is not seen
in other dementias.
Abnormal ratios
• NAA-to-creatine: <1.6
• NAA-to-choline: <1.2
• Choline-to-creatine: >1.5
Interfering factors MRS is a technically complex imaging modality. Factors that
affect results include nonuniformity of magnetic fields and
variability among subjects, age groups, and developmental
stages in infants. Over the past decade, concerted efforts
have been made to standardize acquisition protocols across
laboratories.
Cross-references Magnetic Resonance Imaging
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190 Laboratory Medicine in Psychiatry and Behavioral Science
Magnetic resonance spectroscopy (MRS) (continued)
Agarwal N, Port JD, Bazzocchi M, et al: Update on the use of MR for assessment and diagnosis of psychi-
atric diseases. Radiology 255:23–41, 2010
Currie S, Hadjivassiliou M, Craven IJ, et al: Magnetic resonance spectroscopy of the brain.Postgrad Med
J 89(1048):94–106,
2013
Gharzeddine K, Hatzoglou V, Holodny AI, Young RJ: MR Perfusion and MR spectroscopy of brain neo-
plasms. Radiol Clin North Am 57(6):1177–1188, 2019
Gupta RK, Jobanputra KJ, Yadav A: MR spectroscopy in brain infections.Neuroimaging Clin N Am
23(3):475–498,
2013
Oz G, Alger JR, Barker PB, et al: Clinical proton MR spectroscopy in central nervous system disorders.
Radiology 270(3):658–679,
2014
Schmitz B, Wang X, Barker PB, et al: Effects of aging on the human brain: a proton and phosphorus MR
spectroscopy study at 3T. J Neuroimaging 28(4):416–421, 2018
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191 Laboratory Tests
Mammography
Type of test Imaging
Background and explanation
of test
Mammography is an X-ray examination of the breast and
surrounding soft tissue used to detect masses too small to
be palpable by clinical breast exam. Screening mammogra
-
phy has been the subject of a great deal of controversy in
medicine because of concerns that the harms of false-
positive results outweigh the benefits. In females of average
breast cancer risk, however, screening is known to reduce
breast cancer mortality.
For patients who have symptoms, palpable masses, or a his-
tory of breast cancer or abnormal mammogram, a diagnos-
tic mammogram is performed instead of a screening exam.
A relatively new enhancement to the standard mammo-
gram—three-dimensional (3D) mammography, or breast
tomosynthesis—involves capture of multiple breast images
in different planes that are then reconstructed digitally into
3D images that improve the accuracy of detection and re
-
duce false-positive rates, particularly in patients with dense
breast tissue. Another enhancement is contrast-enhanced
digital mammography, which is utilized to stage newly di
-
agnosed breast cancer and to evaluate response to chemo-
therapy.
Relevance to psychiatry and
behavioral science
The incidence of brain metastases among females with met-
astatic breast cancer ranges from 10% to 30%. Breast cancer
that metastasizes to the brain is more likely to involve triple-
negative tumors and/or tumors overexpressing HER2.
Clinical symptoms of brain metastases include headaches,
memory problems, mood or personality changes, seizures,
stroke or TIA, and impaired sensation and motor function.
Preparation of patient Radiation exposure for mammography is minimal. The test
involves compression of each breast between plates for sev-
eral seconds while each image is acquired, which is uncom-
fortable for most females. Patients should be instructed not
to apply deodorant, powder, perfume, or lotion to the un-
derarm area on the day of the test because these may ob-
scure the images obtained. Patients with painful breasts
due to fibrocystic breast disease may benefit from abstain-
ing from caffeinated beverages in the week before the test
to reduce breast tenderness.
Indications Testing recommendations of the American Cancer Society
are as follows:
• Females at average risk of breast cancer* have the option
of starting annual screening mammography between
ages 40 and 44.
• Females ages 45–54 should undergo annual screening
mammography.
• Females age 55+ may switch to every-other-year mam-
mography or continue annual mammography.
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