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62 Laboratory Medicine in Psychiatry and Behavioral Science
Cerebrospinal fluid analysis (continued)
Contraindications to LP
(continued)
• Midline shift on CT or MRI
• Poor visualization of the fourth ventricle or quadrigem-
inal cistern on CT or MRI
• INR >1.5
• Platelet count < 50,000/mm
3
• Lumbar skin or tissue infection
Reference range See entries for individual CSF tests.
Critical findings See entries for individual CSF tests.
Abnormal findings See entries for individual CSF tests.
Interfering factors Specimen handling: Samples should be examined as soon as
possible or frozen until examination. Freeze/thaw cycles
may interfere with special tests such as amyloid-β.
Cross-references Encephalitis, Viral
Meningitis
Multiple Sclerosis
See entries for individual CSF tests.
Irani DN: Ce rebrospinal Fluid in Clinical Pra ctice. Philadelphia, PA, Saunders Elsevier, 2009
Seehusen DA, Reeves MM, Fomin DA: Cerebrospinal fluid analysis. Am Fam Physician 68:1103–1108,
2003
https://t.me/med1917
63 Laboratory Tests
Cerebrospinal fluid cell count and differential
Type of test CSF sampling by lumbar puncture
Background and explanation
of test
CSF cell counts include the number of RBCs, number of
WBCs, and cell types. Normally, the CSF is acellular, con
-
taining only a small number of lymphocytes and monocytes
in a ratio of 7:3 in adults. The total cell count is a sensitive
indicator of acute inflammation in the CNS. An increase in
the number of WBCs in the CSF is called pleocytosis.
Relevance to psychiatry and
behavioral science
The CSF cell count and differential is an essential component
of the workup for mental status changes, delirium, and sei
-
zures in cases in which an infectious or inflammatory cause
is suspected. Specific causative agents can be identified in tu
-
berculosis, neurosyphilis, and Lyme disease, among many
other conditions.
Preparation of patient See Cerebrospinal Fluid Analysis.
Indications See Cerebrospinal Fluid Analysis.
Reference range Adults: 0–5 WBCs/μL
• 40%–80% lymphocytes
• 15%–45% monocytes
• 0%–6% neutrophils
RBCs: normally not present, although they may be found in
a traumatic tap
Critical value(s) >20 neutrophils (polymorphonuclear leukocytes)
Abnormal findings Increased neutrophils: meningitis (bacterial, early viral, early
tubercular, fungal), amoebic encephalomyelitis, early cere
-
bral abscess, reaction to CNS hemorrhage, injection of foreign
substances into the subarachnoid space (chemotherapeutic
agents, contrast dye), CSF infarct, metastatic tumor in contact
with CSF, reaction to repeated lumbar puncture
Increased lymphocytes: meningitis (viral, tubercular, unusual
bacteria such as Listeria), meningoencephalitis (syphilis),
CNS parasites, multiple sclerosis (with reactive lympho-
cytes), encephalopathy of drug abuse, Guillain-Barré syn-
drome, acute disseminated encephalomyelitis, meningitic
sarcoidosis, human T-lymphotropic virus type III (HTLV-III),
aseptic meningitis, fungal meningitis, polyneuritis
Increased monocytes: chronic bacterial meningitis, toxoplas-
mosis, amoebic meningitis, multiple sclerosis, brain abscess
rupture
Increased plasma cells: acute viral infection, multiple sclerosis,
sarcoidosis, meningoencephalitis (syphilis), subacute scle-
rosing panencephalitis, tubercular meningitis, parasitic infes-
tation, Guillain-Barré syndrome, lymphocytic reactions
Presence of eosinophils: certain infections (parasitic, fungal,
rickettsial), idiopathic hypereosinophilic syndrome, reac-
tion to foreign materials in CSF such as shunts or drugs, sar-
coidosis
https://t.me/med1917
64 Laboratory Medicine in Psychiatry and Behavioral Science
Cerebrospinal fluid cell count and differential (continued)
Abnormal findings
(continued)
Presence of malignant cells: primary or metastatic cancers
Presence of blast cells: acute leukemia
Presence of macrophages: meningitis (tubercular or viral),
reactions to blood, foreign materials, or lipids in CSF
Interfering factors Traumatic tap, improper specimen handling
Cross-references Encephalitis, Viral
Lyme Disease
Meningitis
Syphilis
Tuberculosis
Irani DN: Cerebrospinal Fluid in Clinical Practice. Philadelphia, PA, Saunders Elsevier, 2009
Reiber H, Peter JB: Cerebrospinal fluid analysis: disease-related data patterns and evaluation programs.
J Neurol Sci 184:101–122, 2001
Seehusen DA, Reeves MM, Fomin DA: Cerebrospinal fluid analysis. Am Fam Physician 68:1103–1108,
2003
https://t.me/med1917
65 Laboratory Tests
Cerebrospinal fluid cytology
Type of test CSF sampling by lumbar puncture
Background and explanation
of test
This test detects and characterizes malignant cells present in
the CSF.
Relevance to psychiatry and
behavioral science
CSF cytology is requested when CNS malignancy is sus-
pected to underlie mental status changes, delirium, or sei-
zures.
Preparation of patient See Cerebrospinal Fluid Analysis.
Indications • Clinical signs of carcinomatous meningitis
• Radiographic evidence of brain metastases
Reference range No malignant cells
Critical value(s) None
Increased levels Primary or metastatic malignancy
Decreased levels Not applicable
Interfering factors Improper specimen handling
Cross-references Brain Tumor
Cerebrospinal Fluid Analysis
Meningitis
Irani DN: Cerebrospinal Fluid in Clinical Practice. Philadelphia, PA, Saunders Elsevier, 2009
Reiber H, Peter JB: Cerebrospinal fluid analysis: disease-related data patterns and evaluation programs.
J Neurol Sci 184:101–122, 2001
Seehusen DA, Reeves MM, Fomin DA: Cerebrospinal fluid analysis. Am Fam Physician 68:1103–1108,
2003
https://t.me/med1917
66 Laboratory Medicine in Psychiatry and Behavioral Science
Cerebrospinal fluid glucose
Type of test CSF sampling by lumbar puncture
Background and explanation
of test
Many diseases are associated with decreased CSF glucose
because it is consumed during the pathological process. The
normal range of CSF glucose is related to the serum glucose
level in the 1–4 hours before the procedure.
Relevance to psychiatry and
behavioral science
CSF glucose is an essential component of basic CSF analysis
in the workup of mental status changes, delirium, or sei
-
zures.
Preparation of patient See Cerebrospinal Fluid Analysis.
Indications See Cerebrospinal Fluid Analysis.
Reference range Adults: 45–80 mg/dL (about two-thirds of serum glucose
level)
Critical value(s) Levels < 40 mg/dL are always pathological in adults.
Increased levels • Cerebral hemorrhage
• TBI
• Hyperglycemia or diabetic coma
• Hypothalamic lesion
• Increased intracranial pressure
• Uremia
Decreased levels CNS infection: abscess, coccidioidomycosis, encephalitis,
meningitis, neurosyphilis, toxoplasmosis, tuberculoma
CNS cancer: tumor, leukemia, lymphoma, melanomatosis,
meningeal carcinomatosis
CNS inflammatory/autoimmune disease: sarcoidosis, lupus
myelopathy, rheumatoid arthritis
Other CNS diseases: GLUT1 deficiency syndrome, hypogly-
cemia, increased intracranial pressure, subarachnoid hem-
orrhage
Interfering factors Hyperglycemia raises CSF glucose. Specimen must be ex-
amined by the lab immediately to avoid spurious results
from glycolysis.
Cross-references Cerebrospinal Fluid Analysis
Encephalitis, Viral
Meningitis
Irani DN: Cerebrospinal Fluid in Clinical Practice. Philadelphia, PA, Saunders Elsevier, 2009
Reiber H, Peter JB: Cerebrospinal fluid analysis: disease-related data patterns and evaluation programs.
J Neurol Sci 184:101–122, 2001
Seehusen DA, Reeves MM, Fomin DA: Cerebrospinal fluid analysis. Am Fam Physician 68:1103–1108, 2003
https://t.me/med1917
67 Laboratory Tests
Cerebrospinal fluid lactate
Type of test CSF
Background and explanation
of test
CSF lactate, which is independent of blood lactate, is a prod-
uct of anaerobic metabolism. It reflects the degree of oxygen
deprivation in brain tissue.
Relevance to psychiatry and
behavioral science
This test is usually ordered when a lumbar puncture is per-
formed on an inpatient, often in the critical care setting. The
result can be used in the differential diagnosis of meningitis
etiology and in gauging the severity of TBI.
Preparation of patient See Cerebrospinal Fluid Analysis.
Indications • Distinguishing bacterial meningitis from other causes of
meningitis
• Monitoring severe head injury
Reference range Adults: 10–22 mg/dL
Critical value(s) Increased CSF lactate after TBI suggests poor prognosis.
Increased levels • Bacterial meningitis (>38 mg/dL)
• Viral meningitis: lactate level generally lower
• Brain abscess or tumor
• Cerebral ischemia
• TBI
• Seizure
• Stroke
• Increased intracranial pressure
Decreased levels Not applicable
Interfering factors Because RBCs contain significant amounts of lactate, a trau-
matic tap may yield false-positive results. Specimens cannot
be hemolyzed or xanthochromic.
Cross-references Cerebrospinal Fluid Analysis
Meningitis
Stroke
Irani DN: Cerebrospinal Fluid in Clinical Practice. Philadelphia, PA, Saunders Elsevier, 2009
Reiber H, Peter JB: Cerebrospinal fluid analysis: disease-related data patterns and evaluation programs.
J Neurol Sci 184:101–122, 2001
Seehusen DA, Reeves MM, Fomin DA: Cerebrospinal fluid analysis. Am Fam Physician 68:1103–1108,
2003
https://t.me/med1917
68 Laboratory Medicine in Psychiatry and Behavioral Science
Cerebrospinal fluid protein
Type of test CSF by lumbar puncture
Background and explanation
of test
Under normal circumstances, CSF contains only a small
amount of protein, and the finding of elevated protein reli
-
ably indicates a pathological process. This process can in-
volve changed permeability of the blood-brain barrier,
increased protein production within the CNS, problems with
resorption of CSF at the level of the arachnoid villi, or block
-
age of CSF flow. Special protein studies may be used to deter-
mine the composition of protein (protein electrophoresis or
oligoclonal bands by high-resolution serum protein electro
-
phoresis, isoelectric focusing/ immunofixation) or to identify
pathological processes such as myelin breakdown (myelin ba
-
sic protein).
Relevance to psychiatry and
behavioral science
Mean CSF protein levels are elevated in several conditions of
interest to neuropsychiatrists, including bacterial meningitis
(mean protein level 418 mg/dL), cerebral hemorrhage
(270 mg/dL), brain tumor (115 mg/dL), aseptic meningitis
(77 mg/dL), brain abscess (69 mg/dL), neurosyphilis
(68 mg/dL), multiple sclerosis (43 mg/dL), acute alcoholism
(32 mg/dL), and epilepsy (31 mg/dL).
Preparation of patient See Cerebrospinal Fluid Analysis.
Indications See Cerebrospinal Fluid Analysis.
Reference range Adults ≤40 years: 15–45 mg/dL
Adults 40–50 years: 20–50 mg/dL
Adults 50–60 years: 20–55 mg/dL
Adults >60 years: 30–60 mg/dL
Critical value(s) Values >60 mg/dL in the absence of diabetes or recent stroke
should be thoroughly investigated.
Values >1,000 mg/dL
suggest subarachnoid obstruction of
CSF flow; the lower the block, the higher the value.
Increased levels •
Alzheimer’s disease
• Increased permeability of the blood-CSF barrier
• Meningitis (bacterial, mycobacterial, fungal, or viral)
• Hemorrhage (subarachnoid or intracerebral)
• Stroke
• Endocrine disorders (e.g., diabetes)
• Metabolic disorders
• Drug or alcohol toxicity
• Obstruction to CSF circulation (from tumor, abscess, her-
niated disc, loculated effusion)
• Increased protein synthesis (IgG): multiple sclerosis, sub-
acute sclerosing panencephalitis, neurosyphilis
https://t.me/med1917
69 Laboratory Tests
Cerebrospinal fluid protein (continued)
Increased levels (continued) • Increased IgG synthesis with changed permeability of
blood-CSF barrier: Guillain-Barré syndrome, SLE, periar
-
teritis, chronic inflammatory demyelinating polyneurop-
athy (CIDP)
Decreased levels Low values usually have little clinical significance but may
be seen in CNS trauma with CSF leakage, CSF volume re
-
moval, intracranial hypertension, or hyperthyroidism.
Interfering factors False elevation of protein may be seen with a traumatic tap,
wherein protein level is highest in first tube and progres
-
sively lower in second through fourth tubes. Can be cor-
rected if same tube is used for protein and cell counts by
subtracting 1 mg/dL of protein for every 1,000 RBCs/mm
3
.
Cross-references Alcohol Use Disorder
Brain Abscess
Brain Tumor
Cerebrospinal Fluid Analysis
Cerebrospinal Fluid Glucose
Meningitis
Multiple Sclerosis
Stroke
Syphilis
Irani DN: Cerebrospinal Fluid in Clinical Practice. Philadelphia, PA, Saunders Elsevier, 2009
Reiber H, Peter JB: Cerebrospinal fluid analysis: disease-related data patterns and evaluation programs.
J Neurol Sci 184:101–122, 2001
Seehusen DA, Reeves MM, Fomin DA: Cerebrospinal fluid analysis. Am Fam Physician 68:1103–1108,
2003
https://t.me/med1917
70 Laboratory Medicine in Psychiatry and Behavioral Science
Cerebrospinal fluid tau protein
Type of test CSF
Background and explanation
of test
Tau is a microtubule-associated protein that, when elevated
in CSF, is thought to reflect axonal injury. Tau can be assayed
in CSF as total tau (T-tau) or phosphorylated tau (P-tau),
with levels of the two closely correlated. In the CSF of pa
-
tients with TBI or stroke, there is a marked increase in T-tau
in proportion to the brain injury, with no change in P-tau.
Similarly, with CJD, there is an increase in T-tau up to
20 times that seen in Alzheimer’s disease (AD), with mini
-
mal or no change in P-tau. The only disease characterized by
an increase in P-tau is AD, in which excessive phosphoryla
-
tion at
serine and threonine sites facilitates tau aggregation,
leading to the formation of neurofibrillary tangles.
CSF P-tau is a special study available only through desig-
nated labs. It is usually performed in tandem with CSF
amyloid-β. Tau protein is reported as T-tau and P-tau.
Relevance to psychiatry and
behavioral science
This test is used for selected cases in the workup of cognitive
impairment to provide evidence for or against a diagnosis of
AD. It can distinguish cognitive decline of AD from normal
aging and from alcohol-related cognitive impairment. The
ratio of tau to amyloid-β
1–42
level appears to be superior to
either test alone in differentiating these conditions.
Preparation of patient See Cerebrospinal Fluid Analysis.
Indications Ancillary test used to support diagnosis of AD
Reference range Mean T-tau in control subjects: 212 pg/mL
P-tau <61 pg/mL consistent with non-AD
Critical value(s) Mean T-tau in AD: 534 pg/mL
P-tau >61 pg/mL consistent with AD
Increased levels AD
Decreased levels Not applicable
Interfering factors Not known
Cross-references Alzheimer’s disease
Cerebrospinal Fluid Amyloid β
1–42
Cerebrospinal Fluid Analysis
Dean RA, Shaw LM: Use of cerebrospinal fluid biomarkers for diagnosis of incipient Alzheimer disease
in patients with mild cognitive impairment. Clin Chem 56:7–9, 2009
de Leon MJ, DeSanti S, Zinkowski R, et al: MRI and CSF studies in the early diagnosis of Alzheimer’s dis-
ease. J Intern Med 256:205–223, 2004
Mitchell AJ: CSF phosphorylated tau in the diagnosis and prognosis of mild cognitive impairment and
Alzheimer’s disease: a meta-analysis of 51 studies. J Neurol Neurosurg Psychiatry 80:966–975, 2009
Mounsey AL, Zeitler MR: Cerebrospinal fluid biomarkers for detection of Alzheimer disease in patients
with mild cognitive impairment. Am Fam Physician 97(11):714–715, 2018
https://t.me/med1917
71 Laboratory Tests
Chest X-ray (CXR)
Type of test Imaging
Background and explanation
of test
Routine CXR consists of two views: posteroanterior and left
lateral. Upright films are preferred because supine films do
not show fluid levels. Each film is taken at full inspiration.
The entire procedure takes only a few minutes. Exposure to
radiation is minimal unless the procedure is often repeated.
Although chest CT is superior to CXR in detecting lung dis-
ease related to COVID-19, CXR has been used when CT is
unavailable or where infection control or decontamination
issues have limited its use. CXR findings may be described
as irregular, patchy, hazy, reticular, or ground glass opacities.
The volume of involved lung can also be determined from
CXR.
Relevance to psychiatry and
behavioral science
Many of the conditions that can be diagnosed by CXR have
an association with delirium. In the case of chronic condi-
tions such as tuberculosis, depression may be prominent. In
acute exacerbations of chronic obstructive pulmonary dis
-
ease (COPD), anxiety may be the most pressing symptom.
Chronic changes consistent with emphysema are common
among psychiatric patients, in large part because of the prev
-
alence of smoking. Aspiration pneumonia is common
among patients with dementia, particularly in later stages.
Preparation of patient Clothing and jewelry covering the chest are removed. The
patient wears a hospital gown. Female patients should be
asked about pregnancy. The thyroid gland may be covered
with a lead shield.
Indications •
Delirium of unexplained etiology in an elderly patient
• Dyspnea
•
Acute respiratory illness in any of the following patients:
HIV-positive, age >40 years, age < 40 years with positive
physical exam, dementia, suspected severe acute respi-
ratory syndromes (COVID-19, SARS) or anthrax expo-
sure, febrile neutropenic patient, acute asthma with
suspected pneumonia or pneumothorax, acute COPD
exacerbation with one or more of the following: leukocy-
tosis, pain, history of coronary artery disease, or history
of congestive heart failure (CHF)
Abnormal findings Foreign body, pneumonia, CHF, emphysema, abscess, cysts,
pneumothorax, pleural effusion, TB, sarcoidosis, asbestosis,
coccidioidomycosis, pulmonary embolus. May also detect
bony abnormalities such as scoliosis, osteomyelitis, or oste-
oporosis. COVID-19 findings on CXR include lung tissue
consolidation and ground-glass opacities. Latter may be dif-
ficult to detect on CXR.
Interfering factors Conditions that interfere with patients’ ability to achieve full
inspiration interfere with a complete exam. These include
obesity, pain, CHF, and restrictive lung disease.
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