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202 Laboratory Medicine in Psychiatry and Behavioral Science
Multiple sleep latency test (MSLT) and
maintenance of wakefulness test (MWT) (continued)
Reference range MSLT: Normal mean sleep latency is 10–20 minutes.
MWT: Mean sleep latency is 35 minutes on the 40-minute
test; most individuals with normal sleep can resist falling
asleep and stay awake for the duration.
Positive test MSLT: Mean sleep latency is <8 minutes. Sleep-onset REM
periods occur on more than two naps.
MWT: Mean sleep latency is <8 minutes.
Critical value(s) Mean sleep latency in patients with narcolepsy with cata-
plexy is usually 2–3 minutes.
In this condition, three to five sleep-onset REM periods are
often observed.
Interfering factors Test-retest reliability for MSLT is good for narcolepsy with
cataplexy but not for narcolepsy without cataplexy or for
idiopathic hypersomnia.
Sleep deprivation, which affects individuals attempting to
sleep in artificial laboratory conditions, interferes with both
MSLT and MWT. Anxiety may affect patients’ ability to fall
asleep.
Environmental factors such as light, temperature, and noise
affect test validity. Caffeine or other stimulants and seda
-
tive-hypnotic medications taken before testing may invali-
date results.
Drugs that cause REM sleep rebound when discontinued af-
fect results.
Cross-references Narcolepsy
Polysomnography
Anniss AM, Young A, O’Driscoll DM: Importance of urinary drug screening in the multiple sleep latency
test and maintenance of wakefulness test.J Clin Sleep Med 12(12):1633–1640, 2016
Kluge M, Himmerich H, Wehmeier PM, et al: Sleep propensity at daytime as assessed by multiple sleep
latency tests (MSLT) in patients with schizophrenia increases with clozapine and olanzapine.Schizo-
phr Res 135(1–3):123–127, 2012
Kolla BP, Jahani Kondori M, Silber MH, et al: Advance taper of antidepressants prior to multiple sleep
latency testing increases the number of sleep-onset rapid eye movement periods and reduces mean
sleep latency.J Clin Sleep Med 16(11):1921–1927, 2020
Plante DT: Sleep propensity in psychiatric hypersomnolence: a systematic review and meta-analysis of
multiple sleep latency test findings.Sleep Med Rev 31:48–57, 2017
Rack M, Davis J, Roffwarg HP, et al: The multiple sleep latency test in the diagnosis of narcolepsy. Am J
Psychiatry 162:2198–2199, 2005
Sullivan SS, Kushida CA: Multiple sleep latency test and maintenance of wakefulness test. Chest 134:854–
861, 2008
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203 Laboratory Tests
Osmolality
Type of test Blood, urine
Background and explanation
of test
Osmolality refers to the number of solute particles in 1 kg of
solvent. A related variable—osmolarity—is the number of
solute particles in 1 L of solvent. (A simple mnemonic: os
-
molaRity refers to liteR.) Because measurements of osmolar-
ity are temperature-dependent,
osmolality is the preferred
term for biological systems.
Osmolality is used to evaluate fluid and electrolyte balance,
determine the cause of increased or decreased urine output,
investigate abnormal levels of sodium, and detect the pres
-
ence of ingested toxins such as methanol or acetylsalicylic
acid. Serum and urine osmolality are most often measured at
the same time so that results can be correctly interpreted.
Under normal conditions, the body maintains osmolality
within a certain range through secretion of antidiuretic hor
-
mone (ADH) by
the posterior pituitary.
Serum osmolality is primarily a reflection of sodium con-
centration, whereas urine osmolality is primarily a measure
of waste products (urea and creatinine). Under pathological
conditions, serum osmolality can also reflect glucose levels
(in hyperglycemia) or blood urea levels (in renal failure).
Serum osmolality aids in the evaluation of hyponatremia,
which can be secondary to urinary sodium losses or to in
-
creased fluid in the c
irculation (e.g., from polydipsia,
water
retention, inability of kidneys
to produce a di
lute urine, or
high glucose levels).
Another application of serum osmolality is to compare it
with a calculation of predicted osmolality based on mea
-
surements of the major solutes (sodium, glucose, BUN), a
difference termed the osmolal gap. Such a gap indicates the
presence of additional osmotically active substances such as
ethanol, methanol, or ethylene glycol in the blood.
Relevance to psychiatry and
behavioral science
Acute osmolality changes can be associated with dehydra-
tion, hyperglycemia, alcohol withdrawal, TBI, and other
conditions. Subacute or chronic changes can be seen in
psychogenic polydipsia, tuberculosis, subdural hematoma,
hydrocephalus, AIDS, or multiple sclerosis or be associated
with medications (e.g., diabetes insipidus in patients treated
with lithium, or SIAD in patients treated with antidepres-
sants, antipsychotics, opioids, or carbamazepine). Acute
changes in osmolality can cause delirium or—in extreme
cases—coma.
Preparation of patient None needed
Indications •
Determining cause of hyponatremia
• Assessing fluid and electrolyte balance
• Determining cause of abnormal urine output
• Evaluating suspected SIAD, diabetes insipidus, or psy-
chogenic polydipsia
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204 Laboratory Medicine in Psychiatry and Behavioral Science
Osmolality (continued)
Indications (continued) • Detecting ingested toxins: methanol, ethylene glycol, or
acetylsalicylic acid
Reference range Serum osmolality in adults age ≥17 years: 280–303 mOsm/kg
Urine osmolality in adults age ≥17 years: 50–800 mOsm/kg
Normal ratio of urine to serum osmolality: 3:1
Critical value(s) Serum osmolality <240 mOsm/kg or >320 mOsm/kg
Respiratory arrest can occur at >360 mOsm/kg.
Increased levels • Serum osmolality: dehydration, diabetes insipidus, hy-
perglycemia, hypercalcemia, cerebral lesions, hyperna-
tremic ethanol intoxication, tube feeding, high-protein
diet, hypovolemic shock, poisoning (e.g., methanol,
ethylene glycol)
• Urine osmolality: dehydration, prerenal azotemia, con-
gestive heart failure, SIAD, Addison’s disease, amyloi-
dosis, hypernatremia, high-protein diet
Decreased levels • Serum osmolality: overhydration, primary (psychogenic)
polydipsia, Addison’s disease, acute renal failure, pan
-
hypopituitarism, postoperative states, SIAD
• Urine osmolality: acute renal failure, diabetes insipidus,
primary (psychogenic) polydipsia, compulsive water
drinking, electrolyte derangement (hypokalemia, hy
-
pernatremia, or hypercalcemia)
Interfering factors IV fluids (dextrose and water; sodium) influence osmolality
results.
Specimen hemolysis or lipemic serum influences results.
Several herbs and natural remedies increase osmolality, either
through ADH antagonism or diuretic effects.
Increased serum osmolality can result from ingestion of
mineralocorticoids, osmotic diuretics, insulin, or mannitol.
Abnormal urine osmolality can result from anesthetic agents,
antibiotics, carbamazepine, diuretics, glucose, mannitol, or
X-ray contrast agents.
Urine osmolality is also affected by an aging-related inability
to fully concentrate urine.
Cross-references Adrenal Insufficiency
Diabetes Insipidus
Hyperglycemia
Hyponatremia
Psychogenic Polydipsia
Syndrome of Inappropriate Antidiuresis
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205 Laboratory Tests
Osmolality (continued)
American Association for Clinical Chemistry: Testing.com. Available at: https://www.testing.com. Ac-
cessed August 2021.
ARUP Laboratories: Osmolality, urine, in Lab Test Directory. Salt Lake City, UT, ARUP Laboratories,
2021. Available at: https://ltd.aruplab.com/Tests/Pub/0020228. Accessed August 2021.
ARUP Laboratories: Osmolality, serum or plasma, in Lab Test Directory. Salt Lake City, UT, ARUP Labo-
ratories, 2021. Available at: https://ltd.aruplab.com/Tests/Pub/0020046. Accessed 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
https://t.me/med1917
206 Laboratory Medicine in Psychiatry and Behavioral Science
Oxazepam level
Type of test Blood
Background and explanation
of test
Benzodiazepines are Schedule IV sedative-hypnotic drugs
used to treat anxiety and insomnia. Oxazepam is a drug
with a slow onset of action and a short half-life. It is not
extensively metabolized in the liver. In general, levels of the
drug are checked when either overdose or noncompliance
is suspected or to detect use without a prescription. In the
latter case, a urine drug screen is more likely to be ordered
than a blood level.
Relevance to psychiatry and
behavioral science
Toxicity with chronic benzodiazepine ingestion may mani-
fest as confusion, disorientation, memory impairment,
ataxia, decreased reflexes, and dysarthria. With acute over
-
dose, patients may exhibit somnolence, confusion, ataxia,
decreased reflexes, vertigo, dysarthria, respiratory depres
-
sion, and coma. Treatment is supportive. More serious con-
sequences usually involve co-ingestion of alcohol or other
sedatives, and in these cases, airway management is re
-
quired. The decision to use flumazenil, an antagonist at the
benzodiazepine receptor, is made on a case-by-case basis.
Activated charcoal is no longer recommended, and neither
dialysis nor bowel irrigation has a role in treatment.
Preparation of patient None needed
Indications • Screening for drug use
• Suspicion of overdose
• Signs of toxicity in a treated patient
• Suspected noncompliance with prescribed therapy
Reference range 200–500 ng/mL
Critical value(s) >2,000 ng/mL
Increased levels • Overdose
• Overuse
Decreased levels Noncompliance
Interfering factors None
Cross-references Benzodiazepines
Urine Drug Screen
Kang M, Galuska MA, Ghassemzadeh S: Benzodiazepine toxicity, in StatPearls. Treasure Island, FL, Stat-
Pearls Publishing, 2021. Available at:
https://www.statpearls.com/ArticleLibrary/viewarticle/
30312. Accessed September 2021
Mayo Clinic Laboratories: Test Catalog: Oxazepam (Serax), Serum. Available at: https://
www.mayocliniclabs.com/test-catalog/Overview/90108. Accessed August 2021.
https://t.me/med1917
207 Laboratory Tests
Parathyroid hormone (PTH)
Type of test Blood
Background and explanation
of test
PTH, which is secreted from four small glands on the poste-
rior aspect of the thyroid gland, regulates calcium levels in the
blood and extracellular fluids. When circulating calcium lev
-
els are low, PTH causes calcium to be released from bones and
increases the reabsorption of calcium in the proximal convo
-
luted tubule of the kidney, bringing calcium levels back to the
normal range. When circulating calcium levels are high, the
glands stop producing PTH.
The PTH test is used to diagnose hyperparathyroidism and
hypoparathyroidism, to determine whether abnormal cal
-
cium levels are due to pathology in the parathyroid gland it-
self, and to monitor kidney disease. When the PTH level is
drawn, calcium and creatinine are checked at the same time
for proper test interpretation.
Relevance to psychiatry and
behavioral science
Dysregulation of PTH is associated with altered mental sta-
tus, including delirium.
In hypoparathyroidism, secondary anxiety syndromes can be
seen.
In hyperparathyroidism, depression, fatigue, loss of appetite,
and personality changes can be seen.
Hypoparathyroidism is most often due to parathyroid injury
or accidental removal during thyroid surgery. Several psy-
chotropic drugs affect the PTH level, including lithium, ste-
roids, anticonvulsants, and propranolol.
P repa ra tio n of p at ie nt F as ti ng is no lo ng er re qu ir ed fo r t esti ng . T he ti me at wh ic h t he
sample is drawn may be prescribed, because PTH levels fluc
-
tuate over a 24-hour period. Certain drugs may have to be
discontinued prior to testing.
Indications • Determining cause of calcium derangement
• Evaluating parathyroid function
• Diagnosing hyperparathyroidism
• Diagnosing hypoparathyroidism
• Confirming removal of pathological parathyroid tissue
during surgery
• Monitoring chronic kidney disease
Reference range 15–65 pg/mL
Critical value(s) None
Increased levels • Primary hyperparathyroidism
• Secondary hyperparathyroidism
• Zollinger-Ellison syndrome
• Pseudogout
• Spinal cord injury
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208 Laboratory Medicine in Psychiatry and Behavioral Science
Parathyroid hormone (PTH) (continued)
Increased levels (continued) • Familial medullary thyroid carcinoma
• Multiple endocrine neoplasia (MEN I, IIA, IIB)
Decreased levels • Autoimmune hypoparathyroidism
• Surgical hypoparathyroidism (after thyroidectomy)
• Sarcoidosis
• Hyperthyroidism
• Nonparathyroid hypercalcemia
• Magnesium deficiency
• DiGeorge syndrome
Interfering factors Elevated blood lipids and hemolysis interfere with the PTH
test itself. The time of blood draw influences the results.
Ingestion of milk before
the test may falsely reduce the PTH
result.
Oversupplementation with vitamins A and D reduces PTH.
Drugs that cause increased PTH include anticonvulsants,
corticosteroids, isoniazid, lithium, phosphates (large effect),
estrogen/progestin, ketoconazole, nifedipine, verapamil,
phenytoin, prednisone, and rifampin.
Drugs that cause decreased PTH include aluminum hydrox-
ide, cimetidine, gentamicin, magnesium sulfate, pindolol,
propranolol, and thiazides.
Cross-references Calcium
Hypercalcemia
Hypocalcemia
American Association for Clinical Chemistry: Testing.com. Available at: https://www.testing.com. Ac-
cessed August 2021.
ARUP Laboratories: Parathyroid hormone, intact, in Lab Test Directory. Salt Lake City, UT, ARUP Labo
-
ratories, 2021. Available at: https://www.aruplab.com/Tests/Pub/0070346. Accessed 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
Peacock M: Calcium metabolism in health and disease. Clin J Am Soc Nephrol 5(Suppl):S23–S30, 2010
Verrotti A, Coppola G, Parisi P, et al: Bone and calcium metabolism and antiepileptic drugs. Clin Neurol
Neurosurg 112:1–10, 2010
https://t.me/med1917
209 Laboratory Tests
Phosphate
Type of test Blood
Background and explanation
of test
This test, also known as phosphorus, measures the level of a
dietary nutrient ingested from meat, chicken, fish, eggs, dairy
products, beans, nuts, and cereals. Its absorption in the small
intestine is facilitated by vitamin D. In humans, ≤85% of phos
-
phorus binds to calcium to form bones and teeth; of the re-
mainder, 10% resides in muscle, 1% in nerve tissue, and 1% in
the blood. Phosphate levels are regulated by changes in intes
-
tinal absorption or renal excretion. They are most often
checked along with levels of calcium, PTH, and vitamin D to
diagnose and monitor treatment of conditions that affect both
phosphate and calcium levels.
Phosphates have several important functions in the body, in-
cluding acid-base balance, carbohydrate and lipid metabo-
lism, and storage and transfer of energy. Patients with mild to
moderate phosphate deficiency may be asymptomatic. Those
with severe deficiency may exhibit muscle weakness, reduced
cardiac contractility, reduced platelet function, paresthesias,
and confusion. Patients who are on a ventilator may have
difficulty weaning if phosphate deficiency is present. As the
severity of phosphate deficiency worsens, muscle cramps,
delirium, and seizures may be seen.
Athletes are known to supplement phosphates to improve
performance in high-intensity sports such as cycling and
sprinting. This practice may prove to be dangerous because
high phosphate levels are associated with osteoporosis, car
-
diovascular events, and all-cause mortality. Higher phos-
phate levels—even high-normal levels—contribute to
microvascular dysfunction and may be a cause of aortic ste
-
nosis. Many prescription drugs are known to contain phos-
phates, and this can prove problematic for patients with
kidney failure. Many soft drinks and prepackaged foods are
high in phosphates, possibly contributing to overconsump
-
tion in the general population. Other sources include phos-
phate-containing laxatives and enemas, excessive vitamin D
supplementation, and IV glucose administration.
Relevance to psychiatry and
behavioral science
Alcohol use disorder is associated with decreased phosphate
levels, whereas cirrhosis is associated with increased levels.
Patients who ingest large volumes of soft drinks or large
amounts of prepackaged foods can develop toxic levels of
phosphate.
Preparation of patient Patients should fast for 8–12 hours before testing.
Indications • Abnormal calcium test result
• Symptoms of an abnormal calcium level
• Diagnosing and monitoring kidney disease
• Diagnosing and monitoring bone disorders
• Diagnosing and monitoring GI disease
• Diagnosing parathyroid disease
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210 Laboratory Medicine in Psychiatry and Behavioral Science
Phosphate (continued)
Reference range Adults: 2.7–4.5 mg/dL
Critical value(s) <1.0 mg/dL
Increased levels Kidney failure, excessive intake of phosphate supplements,
hypoparathyroidism, hypocalcemia, excessive vitamin D in
-
take, liver disease and cirrhosis, pulmonary embolism, Ad-
dison’s disease, acromegaly, healing fractures, osteolytic
bone tumors and metastases
Decreased levels Hyperparathyroidism, hypercalcemia, malnutrition, malab-
sorption, vomiting and/or severe diarrhea, acid-base imbal-
ance, serious burns, hypothyroidism, chronic use of antacids
or laxatives, overuse of diuretics, alcohol use disorder, liver
disease, vitamin D deficiency (rickets or osteomalacia),
growth hormone deficiency, continuous IV glucose admin
-
istration, salicylate poisoning, sepsis
Interfering factors Phosphate levels show diurnal fluctuation, with highest lev-
els in late morning and lowest in evening. Seasonal varia-
tions are also seen, with highest values in May and June and
lowest values in winter.
Falsely elevated phosphate levels may be measured if serum
or plasma is not separated from erythrocytes within 1 hour
after blood is drawn.
Many prescription drugs affect phosphate levels; a complete
drug history is needed for proper test interpretation.
Cross-references Anorexia Nervosa
Calcium
Chronic Fatigue Syndrome
Magnesium
Parathyroid Hormone
Renal Function Panel
Vitamin D Level
American Association for Clinical Chemistry: Lab Tests Online. Available at: https://www.testing.com.
Accessed August 2021
Brewer CP, Dawson B, Wallman KE, Guelfi K: Effect of sodium phosphate supplementation on repeated
high-intensity cycling efforts.J Sports Sci 33(11):1109–1116, 2015
Ginsberg C, Houben AJHM, Malhotra R, et al: Serum phosphate and microvascular function in a popu-
lation-based cohort. Clin J Am Soc Nephrol 14(11):1626–1633, 2019
Nelson SM, Sarabia SR, Christilaw E, et al: Phosphate-containing prescription medications contribute to
the daily phosphate intake in a third of hemodialysis patients.J Ren Nutr 27(2):91–96, 2017
Wald DS, Bestwick JP: Association between serum calcium, serum phosphate and aortic stenosis with im-
plications for prevention. Eur J Prev Cardiol 25(5):551–556, 2018
https://t.me/med1917
211 Laboratory Tests
Platelet count
Type of test Blood
Background and explanation
of test
Platelets—also known as thrombocytes—are disc-shaped,
non-nucleated cells that develop in the bone marrow and
spend most of their 1-week lifespan in the circulation. They
have a critical role in blood clotting, vasoconstriction, and
maintenance of small blood vessels. Platelets link these he
-
mostatic functions with inflammatory processes and are
known to have altered function under pro-inflammatory con
-
ditions. Increased platelet activity heightens the risk of
thrombotic events such as heart attack and stroke.
Number and size (volume) of platelets are reported as part of
the CBC. An insufficient number of platelets is associated
with spontaneous bleeding and easy bruising. The mean
platelet volume (MPV) is an indicator of the average age of
platelets; newly formed platelets are larger than old platelets.
Thrombocytosis refers to an increased number of platelets,
whereas thrombocytopenia refers to a decreased number.
Relevance to psychiatry and Psychotropic drugs associated with thrombocytopenia in-
behavioral science clude antidepressants (all classes), antipsychotics (conven-
tional and atypical), anticonvulsants, prescribed stimulants,
acetylcholinesterase inhibitors, β-blockers, and commonly
used analgesics (aspirin, acetaminophen, codeine, ibuprofen,
and others). Drugs associated with thrombocytosis include
amoxapine, clozapine, danazol, donepezil, steroids, immune
globulin, lithium, megestrol, metoprolol, paroxetine, pro-
pranolol, venlafaxine, and zidovudine, among others.
Preparation of patient None needed
Indications • Evaluating bleeding disorders
• Monitoring bone marrow failure
• Abnormal estimated platelet count on blood smear
• Component of coagulation profile
Reference range Adults: 140–400×10
3
/mm
3
The lower limit of normal may be lower for those of Afro-
Caribbean or African ancestry.
Critical values <20×10
3
/mm
3
associated with spontaneous bleeding
>1,000×10
3
/mm
3
associated with myeloproliferative disor-
ders. Patients may have bleeding because of abnormal
platelet function. Half of patients with unexpected increase
in platelet count have malignancy.
Increased levels Essential thrombocytosis, rapid blood regeneration (e.g.,
with acute bleeding), leukemia, myeloproliferative disease,
Hodgkin’s disease, lymphoma, other malignancies, polycy-
themia vera, splenectomy, iron deficiency anemia, acute in-
fection, acute inflammation, rheumatoid arthritis, SLE,
other collagen diseases, chronic pancreatitis, inflammatory
bowel disease, tuberculosis, renal failure, recovery from
bone marrow suppression, and numerous drugs, including
psychotropics
https://t.me/med1917
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