1

Describe the step-by-step process whereby laboratory results are obtained by the medical team

The first step in the process of obtaining laboratory results occurs when the medical team caring for the patient writes an order for a specific laboratory test. This can be either a paper order in the patient’s chart or an electronic order through an online order entry system. A paper order is subsequently processed by the unit clerk who schedules the requested blood draw. The blood draw is generally performed by either the nursing staff or a dedicated phlebotomy team. The blood sample is collected in the appropriate tube and transported to the pathology and laboratory medicine department. The sample is then processed in the appropriate assay. At most institutions, the results are recorded online for medical staff to view, although certain hospitals continue to rely on paper copies of test results, which are kept in the patient’s chart.

2

Describe the process of blood sample collection

Blood samples are collected by some combination of dedicated phlebotomy teams, nurses, technicians, residents, and medical students. Most medical centers have phlebotomy teams whose chief responsibility is to make multiple rounds through the hospital to collect blood samples for ordered laboratory tests. For example, a phlebotomy team may be scheduled to conduct blood draws at 6:00 am , 9:00 am , 10:30 am , 12:00 pm , 2:30 pm , 4:00 pm , and 9:00 pm . During the day, the phlebotomist retrieves laboratory requisitions from the floor clerk, identifies and confirms the correct patient, and proceeds to draw blood from the corresponding patient. The phlebotomist subsequently transports samples to the central distribution station, where it is then sent to the appropriate laboratory (e.g. hematology, chemistry, microbiology).

3

What are A.M. labs?

An important concept to be aware of in the blood sample collection process is that of A.M. labs. This term refers to specimens drawn during the first phlebotomy rounds of the day (such as 6:00 am ). Generally, A.M. labs consist of basic maintenance laboratory tests that are performed daily (or weekly depending on the particular test) and are written for during the preceding day. To illustrate this concept, consider a patient admitted with liver failure. A typical set of A.M. labs (i.e., daily maintenance laboratory tests) may consist of a comprehensive metabolic panel, coagulation tests (prothrombin time [PT], activated partial thromboplastin time [aPTT]), and a complete blood count (CBC). It is not uncommon for some residents to write for daily A.M. labs several days in advance. However, because the patient’s medical condition is constantly changing, they must be careful to avoid ordering unnecessary tests or omitting required ones. When writing for A.M. labs, the abbreviation “AML” may be used. Make sure to include the date as well, for example: “AML 09/28: CBC, coags, etc.”

4

How are blood samples stored for transport to the pathology/laboratory medicine department?

Samples are stored in tubes with special coatings. Each coating is represented by a different color tube top. The type of tube used for a particular blood sample is dictated by the intended laboratory test. The various colored tube tops, their coatings, and common tests for which they are used are listed in Table 4-1 .

5

Describe the difference between routine and STAT orders. How can the receipt of results from STAT be further hastened?

The majority of laboratory requests written on patient care floors are routine . This means that necessary samples are drawn at regularly scheduled hours and processed in the order in which they are received in the pathology department. Although it varies widely depending on the volume of laboratory requests and type of test requested, routine results are usually available the same day (e.g., 4-6 hours for simple blood tests). Results that are required more urgently should be indicated as STAT requests. STAT requests generally have a much faster turn around time (e.g., ≈1 hour for simple blood tests). One may also speed the receipt of laboratory results by personally transporting specimens to the pathology/laboratory medicine department and by phoning the relevant laboratory within the department to request results, which avoids wait time related to posting results online.

6

Which laboratory within the pathology/laboratory medicine department should be called to obtain a particular laboratory result?

The pathology/laboratory medicine department is made up of several component laboratories that use distinctive assays to process different types of samples. To obtain an urgent result by phone or in person, you may want to try to contact the appropriate component laboratory. However, at most institutions if you call the central pathology laboratory, they can transfer you to the appropriate component. The common tests that may be performed by the various component laboratories are outlined in Table 4-2 .

7

Describe the process for retrospectively adding tests to a previously collected blood sample

Additional laboratory tests may need to be performed because of the discovery of new information regarding the patient’s medical condition or because of the accidental omission of tests during order preparation. If this situation arises, be aware that the relevant laboratory within the pathology/laboratory medicine department (see Table 4-2 ) can be contacted to add on an omitted or newly desired assay after a specimen has already been collected. For example, additional electrolyte levels (such as magnesium or phosphorus) are often added on to a basic metabolic panel after a patient is presented during rounds. The ability of the laboratory to comply with your request depends on the amount of time that has passed since sample collection, the amount of sample remaining, and the type of tube in which the sample was collected. If this process is successful, additional blood draws are avoided. In addition, the results will typically be returned much faster than if another blood draw had to be done.

8

When does a laboratory test need to be sent outside of the hospital to obtain results?

Although most major medical centers have fairly comprehensive clinical laboratory facilities, certain specialized tests are “send outs.” Send outs are assays that the institution does not have the capability to perform in-house and thus must be sent to another institution for processing. Results from such tests take much longer to receive (days or weeks rather than hours) owing to increased transport time as well as the specialized nature of the test. Examples of tests that are send outs at many hospitals are uncommon fungal or viral serologic tests (e.g., histoplasma antibody), autoantibody titers (e.g., acetylcholine receptor antibody), enzyme levels (e.g., arylsulfatase A), and hormone levels (e.g., glucagon).

9

What are the two most common metabolic panels encountered on the wards? Compare and contrast their clinical use

The two most commonly used metabolic panels are the basic metabolic panel and the comprehensive metabolic panel. Both panels can be used to identify common electrolyte abnormalities as well as to monitor blood glucose and renal function. The comprehensive metabolic has the added benefit of providing information regarding transaminases, total bilirubin level, and total protein and albumin levels.

10

List other common terms used to describe the basic metabolic panel?

Synonyms for a basic metabolic panel include Chem-8 and SMA-8 (sequential multichannel analysis-8). The Chem-7, SMA-7/SMAC-7, and Metabolic Panel 7 are used at certain institutions. They are identical to the basic metabolic panel with the exception of calcium, which is omitted. Certain institutions also use a Chem-4, which only assesses the levels of sodium, potassium, bicarbonate, and chloride.

11

Describe the components of a basic metabolic panel

The basic panel includes the following components: sodium (Na ⁺ ), potassium (K ⁺ ), chloride (Cl ⁻ ), calcium (Ca ²⁺ ), bicarbonate ( HCO−3HCO−3
HCO 3 −
), blood urea nitrogen, creatinine, and glucose.

12

Describe the components of a comprehensive metabolic panel

The comprehensive metabolic panel includes the eight components that comprise the basic panel as well as albumin, total protein, alanine aminotransferase (ALT or SGPT), aspartate aminotransferase (AST or SGOT), alkaline phosphatase, and total bilirubin. At some institutions, this panel can be ordered by combining a basic metabolic panel and a set of liver function tests.

13

What are liver function tests (LFTs)?

Liver function tests is a term used to denote a series of assays that provide a clinician with a quick assessment of the state of liver function. Generally speaking, the components considered to be part of an LFT include AST, ALT, alkaline phosphatase, total bilirubin (fractionated into conjugated and unconjugated), albumin, and total protein.

14

What are some commonly ordered electrolytes levels that are NOT included in the typical metabolic panels?

Magnesium and phosphorus are the two most common additionally ordered electrolyte levels. The fluctuation in these levels is often related to the changes in other metabolite levels. Although these two electrolyte levels can often provide additional medical information, they are not used as frequently as the other components of typical metabolic panels.

15

List the parameters assessed in a complete blood count (CBC)

The CBC assesses red blood cell count (RBC), hemoglobin (Hgb), hematocrit (Hct), red blood indices, and white blood cell count (WBC). A CBC with a platelet count (CBCP) can also be ordered. A further component of a CBC is the differential; however, many laboratories will only perform this investigation if it is specifically requested (e.g., CBC plus diff).

16

Specify and define the various red blood cell indices

Red blood cell indices are directly measured or derived values that provide information regarding the size and oxygen-carrying capacity of red blood cells. They are included as part of a routine CBC and are useful in the diagnosis of anemia. The various indices in addition to their derivations are listed in Table 4-3 .

17

Discuss the purpose of a white blood cell differential. What additional information may be obtained from this test?

A differential is an automated test that provides the relative frequency of the various types of white blood cells in a given volume of a blood sample. The cell types assayed include neutrophils, lymphocytes, monocytes, basophils, and eosinophils. Results are given as an absolute count and as percentages. Additional information is often obtained in the form of a manual count in which a differential is measured via direct microscopic examination by a pathologist. A manual count is usually only performed when abnormal results are returned by automated count.

18

Depict the shorthand format commonly used for metabolic panels and the CBC

While on the wards, residents and students will commonly be responsible for tracking several days’ worth of laboratory results for multiple patients simultaneously. One way in which medical staff deals with this task is through the use of shorthand diagrams. At first glance, these diagrams may seem difficult to interpret, but with practice they will become second nature and greatly speed the creation of medical documentation and notes for rounds. The typical notations are depicted in Fig. 4-1 .

Shorthand notation for metabolic panels and complete blood cell count (CBC). Alb, Albumin; ALT, alanine aminotransferase; AP, alkaline phosphatase; AST, aspartate aminotransferase; BUN, blood urea nitrogen; Ca ⁺⁺ , calcium; Cl ⁻ , chloride; CR, creatinine; Glu, glucose; 𝐻𝐶𝑂−3HCO−3
H C O 3 −
, bicarbonate; Hct, hematocrit; Hgb, hemoglobin; K ⁺ , potassium; LDH, lactate dehydrogenase; Na ⁺ , sodium; Plt, platelets; 𝑃𝑂−4PO−4
P O 4 −
, phosphate; TBili, total bilirubin; TP, total protein; WBC, white blood cells.

19

List commonly ordered diagnostic tests by system

A variety of commonly ordered diagnostic tests stratified by organ system are outlined in Table 4-4 .

20

List the labs and diagnostic tests regularly ordered for a patient presenting with acute chest pain in the emergency department

The typical patient presenting to the emergency department with acute-onset chest pain requires prompt evaluation to rule out several potentially life-threatening conditions. These conditions include acute coronary syndromes (i.e., unstable angina and myocardial infarction [MI]), pulmonary embolus, and aortic dissection. To effect rapid diagnosis and treatment in these situations, it is important to have an established protocol that includes laboratory and diagnostic tests in place. These laboratory tests are listed in Table 4-5 along with additional tests to consider whether clinical suspicion suggests a particular diagnosis.

21

Discuss the different types of cardiac enzymes used in evaluating patients with possible myocardial ischemia

The term cardiac enzymes refers to a set of serum/plasma biomarkers (enzymes, proteins, or hormones) that are released after myocardial injury/ischemia. A rise in these biomarkers is one of two necessary components for delineating an MI (non-ST-elevation MI [NSTEMI]/ST-elevation MI [STEMI]) from myocardial ischemia (stable/unstable angina). The other necessary component is one of the following: (1) ischemic symptoms, (2) Q waves on an electrocardiogram (ECG), (3) ST elevations or depressions, or (4) coronary artery intervention such as an angioplasty.

In the emergency department (ED) or on the wards, the term cardiac enzymes generally denotes a set of laboratory tests that include troponin (trop) I or T, total creatine kinase (CK), and creatine kinase MB fraction (CK-MB). Trop is the gold standard enzyme because it has been shown to be more sensitive and specific than CK. Because CK can be released from skeletal as well as cardiac muscle, a result for the relatively cardiospecific CK-MB marker is ordered along with total CK.

Other biomarkers of cardiac injury include myoglobin, lactate dehydrogenase (LDH), AST, ALT, and heart-type fatty acid binding protein (H-FABP). However, none of these additional markers are routinely used in the diagnosis of myocardial injury.

22

Describe the kinetics of the different cardiac enzymes

In the setting of myocardial injury, there is a regular rise and fall of the various cardiac enzymes. Elevations of the different enzymes occur with different lag times and the elevations persist for varying lengths of time. The kinetics of the common cardiac enzymes are characterized in Fig. 4-2 .

The rise and fall of cardiac enzyme levels after a myocardial infarction.

(From Antman EM: General hospital management. In Julian DG, Braunwald E (eds): Management of Acute Myocardial Infarction. London, WB Saunders, 1994, with permission.)

23

What is the significance of the term gold standard ?

The term gold standard is used to describe the single diagnostic test that is considered to be definitive for a certain disease process. In theory, this test should be 100% sensitive and 100% specific. In clinical practice there are no ideal tests, but the gold standard is thought to most closely approximate this ideal. This concept is especially important in the evaluation of new diagnostic tests via prospective/retrospective studies. In such studies, the gold standard acts as the basis for comparison of the new test and is used to generate a sensitivity/specificity. It should be noted that although it is considered the definitive test for a disease process, the gold standard is often not the most common test used. The reasons for this seeming disparity are related to issues of cost, safety, and availability. For example, consider the tests available to make a diagnosis of a pulmonary embolus. In this case, pulmonary angiography is the gold standard for diagnosis, but helical computed tomography (CT) is the most commonly used test because it is cheaper, faster, and less risky.

24

What is the utility of brain natriuretic peptide (BNP) in the management of congestive heart failure (CHF)?

BNP is a hormone released by ventricular myocardial cells in response to volume expansion and a related increase in cardiac wall stress. Logically, one would expect an increased BNP level in the volume-expanded state associated with symptomatic congestive heart failure. Therefore, BNP is frequently used to distinguish shortness of breath (SOB) due to symptomatic heart failure from pulmonary causes of SOB. It can also be used to monitor the effects of chronic treatment of heart failure as levels of BNP decrease with effective treatment. Normal values are generally <100 pg/mL, but reference ranges vary between different laboratories. BNP levels in patients with renal failure are unreliable as measures for assessing patients for CHF.

25

Outline a stepwise approach to interpreting ECGs

• ▪
  

  Rate: Divide 300 by the number of large boxes (containing 5 small boxes) between consecutive QRS complexes. 1 box = 300 bpm, 2 boxes = 150 bpm, 3 boxes = 100 bpm, 4 boxes = 75 bpm, 5 boxes = 60 bpm, etc. Normal rate is between 60 and 100 bpm.

  
  
• ▪
  

  Rhythm: If every QRS complex is preceded by a P wave and every P wave is followed by a QRS complex, sinus rhythm is present. If consecutive QRS complexes are equidistant, rhythm is regular.

  
  
• ▪
  

  Axis: Examine the directionality of the QRS complex in leads I and aVF. When the area above the horizontal is greater than the area below the horizontal, there is net positive QRS deflection. When the area above the horizontal is less than the area below the horizontal, there is a net negative QRS deflection. Lead I and aVF findings and the corresponding net axis determination are summarized in Table 4-6 .

  
  
  
  

  TABLE 4-6

  
  

  Electrocardiogram Axis Determination

  
  

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Lead I	Lead aVF	Axis
  +	+	Normal axis (+30° to −90°)
  −	+	Right axis deviation
  +	−	Left axis deviation
  −	−	Extreme axis deviation

   
  
  
  
  
• ▪
  

  Intervals: Important intervals to examine include the PR interval, QRS interval, and the QT interval. Measurement of these intervals, normal values, and associated pathologic conditions is outlined in Table 4-7 .

  
  
  
  

  TABLE 4-7

  
  

  Important Electrocardiogram Intervals

  
  

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Interval	Measurement	Normal Values	Associated Pathology
  PR	Start of P wave to start of Q wave	0.12–0.20 second (<5 small boxes)	>0.20: Atrioventricular (AV) block, ↑vagal tone <0.12: Wolfe-Parkinson-White syndrome
  QRS	Start of Q wave to end of R/S wave	<0.10 second (<3 small boxes)	Bundle branch block, ventricular rhythm (ventricular tachycardia, ventricular flutter), hyperkalemia
  QT	Start of Q wave to end of T wave	>0.45 second * for men, >0.47 second for women	Drugs (amiodarone, Ia/Ic/III antiarrhythmics, tricyclic antidepressants), hypokalemia/Mg/Ca, coronary artery disease

   
  

  * Value applies to corrected QT interval (QTC).

  
  
  
  
• ▪
  

  Atrial chamber enlargement or ventricular wall hypertrophy: Enlargement or hypertrophy of any of the four chambers is detectable on an ECG. Table 4-8 presents the ECG findings and etiologies associated with each.

  
  
  
  

  TABLE 4-8

  
  

  ECG Chamber Enlargement Assessment

  
  

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Chamber	ECG Findings	Etiologies
  RA	V 1 : Biphasic P with large (+) first portion II: P >2.5 mm in height	Suggests more serious right ventricular/pulmonary disease
  LA	V 2 : Biphasic P with large (−) second portion II: P >120 msec in length	Suggests more serious left ventricular disease
  RVH	V 1 : R > S or R > 7 mm RAD/wide QRS	Cor pulmonale, mitral stenosis, tricuspid regurgitation, congenital L to R cardiac shunt
  LVH	V 1 S + V 5 or 6 R: >35 mm aVL R>11 mm LAD/wide QRS	Hypertension, aortic insufficiency, aortic stenosis, hypertrophic cardiomyopathy

   
  

  LA, Left atrium; LAD, left anterior descending artery; LVH, left ventricular hypertrophy; RA, right atrium; RAD, right anterior descending artery; RVH, right ventricular hypertrophy.
  
  
  
  
• ▪
  

  Q waves: Pathologic Q waves represent a lack of electrical activity in an area of myocardial necrosis. Isolated Q waves found in III, aVR, and V ₁ can be normal. Pathologic Q waves are defined as = 0.04 second wide (1 small box) and ≥0.08 second (2 small boxes) deep or one-fourth the size of the corresponding QRS complex. These tend to be found in multiple consecutive leads corresponding to the location of the infarction (i.e., II/III/aVF = inferior, I/V _5–6 /aVL = lateral, V _1–2 = septal, V _3–4 = anterior)

  
  
• ▪
  

  ST depressions: This finding is usually related to subendocardial ischemia or infarction. They are generally accompanied by T wave abnormalities (e.g., T wave inversions). They also may be seen in digoxin toxicity or hypokalemia.

  
  
• ▪
  

  ST elevations: This finding is related to transmural myocardial infarction. They are generally accompanied by T wave abnormalities (e.g., T wave inversions). Also, they may be seen in pericarditis, which is characterized by diffuse ST elevations in nearly every lead. Although ST elevations are generally transient, persistent ST elevations are seen when an aneurysm develops after an acute MI.

  
  
• ▪
  

  T wave inversions: This finding usually represents myocardial ischemia and is generally seen in conjunction with ST elevations or depressions. Other causes of T wave inversions include chronic pericarditis/myocarditis, myocardial contusion due to trauma, and digoxin.

26

What is the difference between the QT and QT _c interval?

The QT interval represents the time elapsed during a single ventricular depolarization (QRS complex) and repolarization (T wave). These events are hastened by an increased heart rate, thus decreasing the measured QT interval. Therefore, to evaluate for QT prolongation independent of the effects of heart rate, one must use the corrected QT interval (QT _c ). QT _c is calculated according to the following formula: QTc=QT/R−R‾‾‾‾‾‾√QTc=QT/√R−R
QT c = QT / R − R
, where R-R = measured R-R interval (time between QRS complexes).

27

Compare and contrast a 24-hour Holter monitor and an event monitor

Both devices are portable ECG monitors used for extended evaluation of rhythm abnormalities on an outpatient basis. They both record using only 2–3 leads, as opposed to the 12 leads used in an ECG. As the name implies, the 24-hour Holter monitor is used only for a 24-hour period, whereas an event monitor is used for a much longer period on the order of weeks to months (generally ≈1 month). The other main difference is related to data recording. The Holter monitor records continuously for 24 hours. In contrast, the event monitor records ECG tracings only when triggered to do so by the patient, usually when he or she is having symptoms.

Holter monitors are useful when a patient is thought to be having frequent episodes of arrhythmias or has unrecognizable/asymptomatic rhythm disturbances. In contrast, event monitors tend to be used in patients having infrequent, but symptomatic, rhythm disturbances. The goal in this case is simply to capture a single episode to help determine further diagnostic studies and proper management.

28

Review the different types of noninvasive diagnostic tests for coronary artery disease (CAD)

Noninvasive diagnostic testing for CAD is an umbrella term that encompasses many modalities for assessing the extent and effect of coronary disease. It has broad applications both in the diagnosis of new CAD and in the assessment, risk stratification, and localization of CAD in patients with documented disease. In simplified terms, in such testing “stress” is generated on the heart through the induction of increased metabolic needs. The resulting effects of this hypermetabolic state are then assessed through an ECG or imaging techniques. Table 4-9 shows the means by which the various stressors induce cardiac stress. The different methods for detecting CAD manifestations after stress are outlined in Table 4-10 and different combinations available for noninvasive CAD testing are reviewed in Table 4-11 .

TABLE 4-9

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