Diagnostic Testing Flashcards by Melissa Morier

Purpose of Diagnostic Tests

Diagnose conditions
Monitor for complications
Track response to treatment
Ultimate goal is to guide treatment decisions

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Screening

-Diagnostic tests are sometimes done in order to screen for a condition
-Screening means the pt may have no manifestations of the disease but may have risk factors
-Sometimes diagnostic test is done because pt is showing signs and symptoms

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For an abnormal result to occur…

-A physiological change has ALREADY TAKEN PLACE in the body

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Screening for health conditions based on..

Who Wilson criteria for screening

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Who Wilson criteria for Screening

-There should be a recognizable latent or early asymptomatic stage
-There should be an accepted treatment recognized for the disease
-*Treatment should be more effective if started early
-The condition should be an important health problem
-The natural history of the condition should be understood
-There should be a policy on who should be treated
-Diagnosis and treatment should be cost effective
-There should be a test that is easy to preform and interpret, is accurate, reliable, sensitive and specific

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Blood testing

-Most common diagnostic tests are performed on blood
-Can collect different types of blood samples depending on what we are wanting to examine/measure

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Blood makeup

-45% of blood is made up of cells (formed elements)
-RBCs, WBCs, Platelets

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RBCs

-Erythrocytes
-Contain hemoglobin
-Responsible for transporting oxygen around the body

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WBCs

-Leukocytes
-Responsible for fighting infections/play vital role in inflammatory response

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Platelets

-Thrombocytes
-Play a vital role in early clotting

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Liquid part of blood

-55%
-Called plasma
-Proteins (albumin, clotting factor, immunoglobulins
-Substances suspended in water (electrolytes, glucose, hormones, bilirubin)

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Whole Blood Tests

-Used when we want to look at the formed elements in the blood
-There will be an anticoagulant in the tube to prevent the blood cells from clumping
- Called Complete blood count or CBC

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Where are whole blood tests sent to

-Samples sent to HEMATOLOGY lab

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Plasma/Serum Tests

-Used when blood is drawn to test electrolytes, hormones, and other substances suspended in plasma
-Tube will contain separator gel which separates plasma from the formed elements after centrifuging

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Where are plasma/serum tests sent

-samples sent to BIOCHEMISTRY lab

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Serum

-The blood clots prior to centrifuging so clotting factors are not in the serum
-Clotting factors removed

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Plasma

-An anticoagulant in the tube prevents clotting so clotting does not occur
-thus plasma contains clotting factor

Manitoba and plasma/serum

-Most labs in Manitoba test on plasma for majority of biochemistry testing
-however interchangeable
-Eg. Serum albumin and plasma albumin measure the same thing

Nurses Draw Blood from

CVADs (central lines)

DSM will reject specimens for analysis due to

-Labelling errors
-Unacceptable specimen quality

Labelling Errors

-identifiers on the specimen label and order do not match
-Pts first and last name and PHIN are not on the test requisition and specimen label
-Name of ordering professional is not on the test requisition
-Location of patient is not on the test requisition

Unacceptable specimen quality examples

-inappropriate transport
-inappropriate storage
-inappropriate container or specimen tubes
-inappropriate preservative
-hemolysis
-lipemia
-insufficient quantity for analysis

Analyzing results steps

Ensure the result is accurate
Determine if the result is significant (hardest part)

Tests can be inaccurate due to…

Interfering factors
-should confirm accuracy of a result BEFORE taking any action related to the result

Most Common Reasons for an Inaccurate Result

-Diluted or quantity insufficient samples -Improper timing -Hemolysis

What is Hemolysis ?

-The breaking of red blood cells during sample collection or handling and results in release of Intracellular contents into the plasma -Eg shaking, dropping specimen

Hemolysis can alter results in

-Potassium (falsely high), most common test affected by hemolysis, when RBC are broken, potassium is released into plasma = have to draw new sample before concluding whether pt is hyperkalemic or not -PTT (falsely high) -Troponin T (falsely low)

Determining Significance Steps

-Look for cues in normal ranges -Know the relevant treatment goals and lab result trends for that patient (determine if it’s okay for them to be out of range) -Asking key questions (what is the pt’s baseline and recent trends? Does this result represent a potential serious time sensitive issue)

Sodium normal range

135-145

Sodium critical value

Less than 120 or over 160

Potassium normal range

3.5-5.0mmol/L

Potassium Critical Value

Less than 2.5, over 6.5

Creatine Kinase Normal Range

52-175 -no critical value

Why is potassium so critical

-important electrolyte in cardiac conduction and arrhythmia can happen whether it is high or low -do not ignore a low potassium level just because pt is on med known to cause low potassium like some diuretics

Creatine Kinase

-type of muscle enzyme -in males normal range is more than 100units and elevations over 500units are considered mild -only considered severe if Over 5000 -like this, some elevations are not causing serious health risks but are simply used to direct treatment

Therapeutic/Target test Ranges

-In some cases the patient is receiving treatment in order to create an abnormal lab result -Eg. Anticoagulants increasing INR (less likely to clot)

INR Test

-International normalized ratio -test used to measure clotting -normal range 0.9-1.1 -we want patients INR to be 2-3x the normal range if taking anticoagulants -abnormal but considered therapeutic

PT, INR, PTT levels

-measure clotting such as prothrombin time, international normalized ratio or partial thromboplastin time -will be elevated when the patient is begging anticoagulated with certain meds -higher the value, slow coagulation time

HGBA1c

Normal range: 4-6% Target range: 7% -tested in diabetics = average blood glucose

Hgb Normal Range

-140-180g/L in males -120-160g/L in females

An acute drop in hemoglobin can be a sign of..

-a patient experiencing acute blood loss -will assess patient for associated risk factors and signs and symptoms of bleeding before notifying the MD

Hgb can be affected by

-how hydrated a patient is -therefore Iv treatment can explain subtle variations