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212 Laboratory Medicine in Psychiatry and Behavioral Science
Platelet count (continued)
Decreased levels Idiopathic thrombocytopenic purpura, various heritable
syndromes, anemia (pernicious, hemolytic, aplastic), throm
-
bopoietin deficiency, dilutional effect of a large blood trans-
fusion, infection (viral, bacterial, or rickettsial), congestive
heart failure, congenital heart disease, chemotherapy or
radiation therapy, exposure to DDT and other chemicals, HIV
infection, bone marrow disease (leukemia, carcinoma, myelo
-
fibrosis), disseminated intravascular coagulation, thrombotic
thrombocytopenic purpura, preeclampsia, eclampsia, alco
-
hol use disorder, excessive alcohol ingestion, hypersplenism,
renal insufficiency, antiplatelet antibodies, toxic effects of
drugs (not dose-dependent), psychotropic drugs listed in the
Relevance section above
Interfering factors Platelet clumps or very large platelets make automated
counts inaccurate; in these cases, manual inspection should
be used.
Thrombocytosis may be seen at high altitudes, in winter, or
after strenuous exercise, trauma, or excitement.
Thrombocytopenia may be observed before menstruation
and during pregnancy.
Cross-references Complete Blood Count
Thrombocytopenia
Thrombocytosis
American Association for Clinical Chemistry: Testing.com. Available at: https://www.testing.com. Ac-
cessed August 2021.
Fischbach FT, Fischbach MA: A Manual of Laboratory and Diagnostic Tests, 10th Edition. Philadelphia,
PA, Wolters Kluwer Health/Lippincott Williams and Wilkins, 2018
Iyer KS, Dayal S: Modulators of platelet function in aging.Platelets 31(4):474–482, 2020
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213 Laboratory Tests
Polysomnography
Type of test Neurophysiology
Background and explanation
of test
Polysomnography is an overnight study in which multiple
parameters are monitored while the patient sleeps, includ
-
ing electroencephalography, eye movements (measured by
electro-oculogram), electrocardiography, electromyography,
respiratory effort of chest and abdomen, oral/nasal airflow,
and oxygen saturation. Digital data capture has simplified
the detection of sleep-related events and the scoring of sleep
stages and events.
Although several disorders can be detected using polysom-
nography, the primary indication for this procedure is to
confirm the clinical diagnosis of obstructive sleep apnea
(OSA). For this purpose, apnea and hypopnea events are
monitored. Apnea occurs when airflow stops for ≥10 sec
-
onds. Hypopnea occurs when airflow is reduced by ≥30%
for ≥10 seconds with accompanying oxygen desaturation of
≥3%. The apnea-hypopnea index (AHI) is the sum of apneas
and hypopneas per hour of sleep.
To reduce cost and make testing more convenient, ambula-
tory (at-home) recording systems have been developed and
are in use, but lab-based PSGs remain the gold standard. At-
home testing can support but not exclude an OSA diagnosis.
Relevance to psychiatry and
behavioral science
A PSG study can aid in diagnosing and characterizing sev-
eral conditions that affect psychiatry patients, including
nocturnal panic attacks, treatment-resistant depression in
the context of sleep apnea, cognitive impairment with noc
-
turnal desaturation, and various parasomnias. In cogni-
tively healthy elderly patients, OSA has been shown to be
associated with increased amyloid burden in follow-up.
Preparation of patient The patient stays overnight in the sleep laboratory while un-
dergoing monitoring. Video recording is also needed if the
referring question relates to REM sleep behavior disorder or
seizure. If the patient has OSA and the intention is to initiate
continuous positive airway pressure (CPAP) treatment,
CPAP can be used for part of the testing night to determine
individual settings, although these “split-night” studies
carry the risk of overestimating severity of sleep apnea in
patients with mild disease.
Indications • Evaluating sleep-disordered breathing
• Confirming diagnosis of restless legs syndrome
• Detecting periodic limb movements of sleep
• Evaluating REM sleep behavior disorder
• Confirming nocturnal seizures
• Confirming nocturnal panic attacks (and excluding
seizures)
• Confirming other parasomnias, such as sleepwalking
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214 Laboratory Medicine in Psychiatry and Behavioral Science
Polysomnography (continued)
Indications (continued) A PSG is also recommended for patients with a history of
stroke, patients with a neuromuscular or pulmonary disor
-
der with hypoventilation, and patients with congestive
heart failure who take opioid medications.
Reference range • Per laboratory report, normal values for sleep onset and
offset times, hours of sleep, proportion of each sleep
stage, and number of arousals during sleep
• Absence of periodic leg movements
• Oxygen saturation >90%
• Absence of abnormal snoring
• Absence of electrocardiographic rate and rhythm distur-
bances
• AHI <5 apneas/hypopneas per hour in a patient with
OSA symptoms (<10 per hour after age 60 years)
Critical value(s) • Mild sleep apnea: AHI 5 to <15
• Moderate sleep apnea: AHI 15 to <30
• Severe sleep apnea: AHI ≥ 30
Abnormal test • Apneas
• Hypopneas
• Desaturation
• Disrupted sleep architecture
• Abnormal leg movements
• Abnormal behaviors
Interfering factors Caffeine or other stimulants and sedative-hypnotic medica-
tions taken before testing can significantly interfere with test
results.
Cross-references Obstructive Sleep Apnea
Restless Legs Syndrome
Andrade L, Paiva T: Ambulatory versus laboratory polysomnography in obstructive sleep apnea: com-
parative assessment of quality, clinical efficacy, treatment compliance, and quality of life.J Clin Sleep
Med 14(8):1323–1331, 2018
Boulos MI, Jairam T, Kendzerska T, et al: Normal polysomnography parameters in healthy adults: a sys-
tematic review and meta-analysis.Lancet Respir Med 7(6):533–543, 2019
Kapur VK, Auckley DH, Chowdhuri S, et al: Clinical Practice Guideline for Diagnostic Testing for Adult
Obstructive Sleep Apnea: an American Academy of Sleep Medicine clinical practice guideline.J Clin
Sleep Med 13(3):479–504, 2017
Rouse JK, Shirley SR, Holley AB, et al: Split-night polysomnography overestimates apnea-hypopnea in-
dex in high-risk professions. Mil Med 184(5–6):e137–e140, 2019
Rundo JV, Downey R III: Polysomnography. Handb Clin Neurol 160:381–392, 2019
Sharma RA, Varga AW, Bubu OM, et al: Obstructive sleep apnea severity affects amyloid burden in cog-
nitively normal elderly: a longitudinal study. Am J Respir Crit Care Med 197(7):933–943, 2018
Veasey SC, Rosen IM: Obstructive sleep apnea in adults. N Engl J Med 380(15):1442–1449, 2019
https://t.me/med1917
215 Laboratory Tests
Positron emission tomography, brain
Type of test Imaging, nuclear medicine
Background and explanation
of test
In PET scanning, a gamma ray–emitting isotope (radionu-
clide) is coupled with a biologically active molecule or drug
of interest, and the concentration of radionuclide activity is
subsequently mapped to show the location of the coupled
molecule/drug. If the coupled molecule is FDG, the scan
yields information about tissue metabolic activity. Other
isotopes are available for use with PET, including
15
O,
13
N,
and
11
C, but
18
F coupled with glucose (FDG) is most often
used in clinical scanning.
18
F has a long enough half-life that
it is possible to produce the isotope at an off-site facility,
which makes FDG more accessible to clinical imaging cen
-
ters. In addition, it is less critical that the patient’s mental
state or activity be standardized with this isotope than with
isotopes with very short half-lives, such as
15
O. PET scan-
ning in clinical and research settings normally also includes
anatomical imaging in the form of CT or MRI to
co-register
metabolic findings with anatomy.
Significant progress in the development of molecular probes
over the past decade has enabled researchers to visualize
brain pathology such as amyloid-β deposition, tau protein
deposition, microglial activation and neuroinflammation,
and synaptic density. For example, TSPO, a marker of
neuroinflammation, has been found to be consistently
elevated in unmedicated patients with major depression.
Other insights have been gained from imaging dopami
-
nergic, serotonergic, and other neuroreceptor functions in
schizophrenia, depression, bipolar disorder, substance use
disorders, eating disorders, OCD, ADHD, and autism spec
-
trum disorder. Uniquely, PET can measure P-glycoprotein
pump function in vivo, and this capability is expected to
yield important insights about the blood-brain barrier in
neuropsychiatric disease.
Relevance to psychiatry and Tracers for amyloid-β PET and tau PET have now been FDA
behavioral science approved.
Other applications of PET to neuropsychiatric diseases re-
main investigational.
Preparation of patient Patients should follow a very-low-carbohydrate diet for
24 hours before scan and should not eat or drink anything
but water for 6 hours before scan. Water should be encour
-
aged, as much as tolerated. Routine medications should be
taken. Diabetes medication should be taken no less than
4 hours before scan.
Indications • Informing differential diagnosis of dementia subtypes
• Presurgical evaluation for epilepsy
• Detecting cancer
• Evaluating cardiac blood flow
• Research protocols
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216 Laboratory Medicine in Psychiatry and Behavioral Science
Positron emission tomography, brain (continued)
Normal result • Requires individual interpretation according to study
protocol
• In general, no abnormal accumulation of radiotracer and
no unexpected gaps in visualization of tracer
Abnormal result • Temporoparietal hypometabolism in Alzheimer’s dis-
ease, often more marked in one hemisphere
• Frontal or frontotemporal hypometabolism in frontal
lobe dementia
• Abnormal uptake reflecting deposition of amyloid and
tau in neurodegenerative diseases
• Increased uptake in vascular tumor
• Abnormal uptake in seizure focus, dependent on time
since seizure
Interfering factors Hypoglycemia can affect glucose metabolism as imaged by
FDG-PET.
Movement of the patient of >1 cm can result in motion
artifact.
Cross-references Dementia
Cai Z, Li S, Matuskey D, et al: PET imaging of synaptic density: a new tool for investigation of neuropsy-
chiatric diseases.Neurosci Lett 691:44–50, 2019
Coughlin JM, Horti AG, Pomper MG: Opportunities in precision psychiatry using PET neuroimaging in
psychosis. Neurobiol Dis 131:104428, 2019
Gianni AD, De Donatis D, Valente S, et al: Eating disorders: do PET and SPECT have a role? A systematic
review of the literature.Psychiatry Res Neuroimaging 300:111065, 2020
Hellwig S, Domschke K: Update on PET imaging biomarkers in the diagnosis of neuropsychiatric disor-
ders.Curr Opin Neurol 32(4):539–547, 2019
Jain P, Chaney AM, Carlson ML, et al: Neuroinflammation PET imaging: current opinion and future di-
rections. J Nucl Med 61(8):1107–1112, 2020
Leuzy A, Chiotis K, Lemoine L, et al: Tau PET imaging in neurodegenerative tauopathies: still a chal-
lenge.Mol Psychiatry 24(8):1112–1134, 2019
Meyer JH, Cervenka S, Kim, et al: Neuroinflammation in psychiatric disorders: PET imaging and prom-
ising new targets.Lancet Psychiatry 7(12):1064–1074, 2020
Mitelman SA: Transdiagnostic neuroimaging in psychiatry: a review. Psychiatry Res 277:23–38, 2019
Pagani M, Carletto S, Ostacoli L: PET and SPECT in psychiatry: the past and the future.Eur J Nucl Med
Mol Imaging 46(10):1985–1987, 2019
Slough C, Masters SC, Hurley RA, Taber KH: Clinical positron emission tomography (PET) neuroimaging:
advantages and limitations as a diagnostic tool.J Neuropsychiatry Clin Neurosci 28(2):A4–A71, 2016
Toyohara J: Importance of P-gp PET imaging in pharmacology. Curr Pharm Des 22(38):5830–5836, 2016
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217 Laboratory Tests
Potassium
Type of test Blood
Background and explanation
of test
Potassium is an electrolyte present in all body fluids but
concentrated inside cells, where it functions to regulate wa
-
ter and acid-base balance, participates in nerve conduction,
and stimulates contraction of muscle cells. Along with cal
-
cium and magnesium, potassium controls cardiac output
(heart rate and force of contraction). Potassium is taken in
from dietary sources and excreted primarily through the
glomeruli of the kidneys. Mildly decreased potassium levels
are common, particularly among patients treated with di
-
uretic medications. Increased potassium levels result pri-
marily from reduced renal function or cellular injury when
intracellular potassium is released into the circulation.
Potassium can be assayed as an individual test but more of-
ten is checked as part of an electrolyte panel, renal panel,
BMP, or CMP.
Relevance to psychiatry and
behavioral science
Severe hyperkalemia (high potassium) or hypokalemia (low
potassium) can be life-threatening conditions requiring ur-
gent intervention. Potassium may be increased with lithium
treatment, with succinylcholine used for ECT, or in acute
starvation (as in anorexia nervosa). Potassium may be de
-
creased in chronic starvation, bulimia, psychogenic vomit-
ing, anabolic steroid abuse, or alcohol use disorder. Patients
with megaloblastic anemia treated with vitamin B
12
or folate
may become potassium depleted and thus require ongoing
replacement.
Preparation of patient Patients should avoid vigorous exercise before blood is
drawn on the day of testing.
Indications • Symptoms of hypokalemia: fatigue, constipation, muscle
twitching, weakness, irregular heart rhythm
• Symptoms of hyperkalemia: nausea, diarrhea, chest pain,
muscle weakness, irregular heart rhythm
• Admission laboratory workup
• Routine component of health screening
• Monitoring patients on diuretic medications
• Monitoring kidney disease
• Monitoring patients on dialysis or IV therapy
Reference range 3.5–5.1 mEq/L
Critical value(s) <2 mEq/L associated with ventricular fibrillation
>7 mEq/L associated with muscular irritability (including
myocardium, with peaked T waves)
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218 Laboratory Medicine in Psychiatry and Behavioral Science
Potassium (continued)
Increased levels • Renal failure, dehydration, renal obstruction, cellular
injury (burns, trauma, surgery tissue ischemia, chemo
-
therapy), intravascular hemolysis, metabolic acidosis, di-
abetic ketoacidosis, severe acute starvation (e.g., anorexia
nervosa), status epilepticus, malignant hyperthermia,
Addison’s disease, rapid potassium infusion, acquired
hyperkalemia (e.g., in SLE or sickle cell disease)
• Drugs: NSAIDs, potassium-sparing diuretics, ACE inhib-
itors, and β-blockers
Decreased levels • Chronic starvation, prolonged IV hydration without
potassium replacement, prolonged vomiting or diarrhea,
fluid loss from intestinal fistula, excessive loss of potas-
sium in urine, loss from draining wounds, chronic heavy
alcohol use, treatment of megaloblastic anemia with vita
-
min B
12
or folate, cystic fibrosis
• Drugs: corticosteroids, β-adrenergic agonists such as
isoproterenol, β-adrenergic antagonists such as clonidine,
antibiotics such as gentamicin and carbenicillin, and the
antifungal agent amphotericin B
Interfering factors Improper specimen handling is an important cause of
spurious potassium elevation in outpatient settings in
which blood must be transported to the laboratory. Regard
-
less of setting, specimen hemolysis can be problematic.
Use of a tourniquet and/or pumping the hand before draw-
ing blood can elevate the potassium level by 20%.
Patients with elevated WBC and platelet counts may also
have
spurious elevation of their potassium level.
Some
diurnal variation is seen in potassium levels, with
values being 0.2–0.4 mEq/L higher in the afternoon and
evening.
Vigorous exercise can transiently increase potassium levels
by 50%; this effect is enhanced by β-blockers.
Cross-references Anorexia Nervosa
Bulimia Nervosa
Hyperkalemia
Hypokalemia
American Association for Clinical Chemistry: Testing.com. Available at: https://www.testing.com. Ac-
cessed August 2021.
Dørup I: Magnesium and potassium deficiency: its diagnosis, occurrence and treatment in diuretic ther-
apy and its consequences for growth, protein synthesis and growth factors. Acta Physiol Scand Suppl
618:1–55, 1994
Fischbach FT, Fischbach MA: A Manual of Laboratory and Diagnostic Tests, 10th Edition. Philadelphia,
PA, Wolters Kluwer Health/Lippincott Williams and Wilkins, 2018
Saxena K: Clinical features and management of poisoning due to potassium chloride. Med Toxicol Ad-
verse Drug Exp 4:429–443, 1989
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219 Laboratory Tests
Prealbumin
Type of test Blood
Background and explanation
of test
In the past, prealbumin was used as a general measure of
nutritional status, but research has demonstrated that preal
-
bumin levels reflect many other factors, including inflam-
mation, infection, and trauma. For this reason, it is no longer
recommended that prealbumin be used to detect malnutri
-
tion. The test may prove to have other uses, however; recent
studies have shown the predictive value of prealbumin in
diseases such as gastric cancer.
Relevance to psychiatry and
behavioral science
Low prealbumin levels may be found in patients with AIDS,
cancer, anorexia nervosa, and failure to thrive, but the utility
of these findings is uncertain. Low prealbumin is a risk fac-
tor for development of delirium.
Preparation of patient None needed
Indications Specific indications to be determined.
Reference range Adults: 18–45 mg/dL
Critical value(s) None
Increased levels High-dose steroids, adrenal gland hyperfunction, high-dose
NSAIDs, Hodgkin’s disease, shigellosis
Decreased levels Protein-calorie undernutrition/malnutrition, inflammation,
infection, trauma, hyperthyroidism, liver disease, cystic
fibrosis, diabetes, protein-losing enteropathies, peritoneal
dialysis, use of amiodarone or estrogens (including oral
contraceptives)
Interfering factors See discussion above.
Cross-references None
American Association for Clinical Chemistry: Testing.com. Available at: https://www.testing.com. Ac-
cessed August 2021.
Hong Y, Seese L, Hickey G, et al: Preoperative prealbumin does not impact outcomes after left ventricular
assist device implantation.J Card Surg 35(5):1029–1036, 2020
Zhang Z, Pereira SL, Luo M, Matheson EM: Evaluation of blood biomarkers associated with risk of mal-
nutrition in older adults: a systematic review and meta-analysis. Nutrients 9(8):829, 2017
Zu H, Wang H, Li C, Xue Y: Preoperative prealbumin levels on admission as an independent predictive
factor in patients with gastric cancer.Medicine (Baltimore) 99(11):e19196, 2020
https://t.me/med1917
220 Laboratory Medicine in Psychiatry and Behavioral Science
Prolactin
Type of test Blood
Background and explanation
of test
Prolactin is an anterior pituitary hormone that functions pri-
marily to promote lactation. Levels are normally high
throughout pregnancy and just after childbirth and are then
maintained at high levels by breastfeeding. The hormone is
present in low concentrations in males and in nonpregnant
females. Prolactin release from the pituitary is regulated at
the level of the hypothalamus. Dopamine inhibits prolactin
production, and when dopamine receptor antagonists are
given, significant elevations can result. Other causes of ele
-
vation include pituitary tumors known as prolactinomas,
epileptic seizures, and anorexia nervosa. Low prolactin
levels can be found in conditions affecting the anterior
pituitary, including craniopharyngiomas, tuberculosis, his
-
toplasmosis, sarcoidosis, hemochromatosis, and a range of
autoimmune conditions.
In females, high prolactin levels are associated with low es-
trogen levels, amenorrhea, infertility, galactorrhea, painful
sexual intercourse, reduced bone mineral density, and hir-
sutism. In males, high levels are associated with decreased
libido, erectile dysfunction, infertility, and abnormal lack of
body and facial hair. Headaches, visual impairment, and
other hormonal deficiencies can be seen with pituitary tu
-
mors that compress surrounding tissues. Low prolactin lev-
els normally do not require treatment.
Relevance to psychiatry and
behavioral science
Serum prolactin levels can help to distinguish generalized
tonic-clonic and complex partial seizures from psychogenic
nonepileptic seizures. For this purpose, blood is drawn 10–
20 minutes after the event, and a baseline level is checked
the following day for comparison. A twofold or greater in
-
crease in prolactin associated with the event is characteristic
of a true seizure. The gold standard for this differential di
-
agnosis is video electroencephalography, but this technol-
ogy is not universally available.
First-generation antipsychotics, risperidone, and paliperi-
done are well known to cause serum prolactin elevations,
with associated symptoms in patients. Aripiprazole and
ziprasidone are thought to be relatively free of this effect.
Other psychotropics that cause elevation include TCAs, the
SSRIs citalopram and escitalopram, and other drugs listed
below in the Increased Levels section.
Preparation of patient Ideally, the blood sample is drawn 3–4 hours after morning
awakening. For use in diagnosing epileptic seizures, the test
sample is drawn 10–20 minutes after the suspected ictal
event, and a baseline sample is drawn >6 hours after the
event, often on the following day.
Indications •
Workup of suspected prolactin elevation based on clini-
cal symptoms
•
Monitoring effects of antipsychotic and selected antide-
pressant drug therapy
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221 Laboratory Tests
Prolactin (continued)
Indications (continued) • Distinguishing generalized tonic-clonic or complex par-
tial seizures from psychogenic nonepileptic seizures
• Determining cause of infertility and/or erectile dysfunc-
tion
• Evaluating anterior pituitary function (with other hor-
mones)
• Follow-up of low testosterone level
• Monitoring effectiveness of treatment for prolactinoma
• Detecting recurrence of prolactinoma
Reference range Nonpregnant adult females: <25 ng/mL
Pregnant females: 80–400 ng/mL
Adult males: <20 ng/mL
Critical value(s) Level of > 200 ng/mL in nonlactating females may indicate
presence of a prolactinoma, although a normal level does
not rule out prolactinoma. High levels may result from anti-
psychotic or other drug treatments.
Increased levels • Prolactinoma
• Pregnancy
• Nursing
• Hypothalamic disease
• Hypothyroidism
• Kidney disease
• Other pituitary tumors and diseases
• Polycystic ovary syndrome
• Recent seizure
• Cocaine withdrawal
• Drugs: antipsychotics, other dopamine-blocking drugs
(e.g., prochlorperazine, metoclopramide), TCAs, SSRIs,
MAOIs, ramelteon, buspirone, alprazolam, morphine,
estrogen, and herbal drugs (e.g., red clover, fenugreek,
fennel)
Decreased levels • Hypopituitarism
• Drugs: dopamine, levodopa, ergot alkaloid derivatives
Interfering factors Stress from illness, trauma, low blood sugar, strenuous exer-
cise, or needle phobia can cause moderate increases in pro-
lactin levels.
Time of sample can affect results: levels rise during sleep
and peak in early morning hours.
Prolactin can form macromolecular complexes with IgG,
leading to false-positive test results.
Cross-references Seizures
https://t.me/med1917
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