What should the chiropractic physician know about lab tests
What should the chiropractic physician know about lab tests?
• Sometimes they are helpful in understanding more about your patient than what you knew before, then again sometimes they do nothing to add or help
• Most of the time the utility of lab tests fall in between
Utility of Lab tests - do to technology there are more tests going on and less physical diagnosis being performed. However, we can find and measure more things than ever before. We did not even know that things exist that are now present today 15 years later. Everyday more things are being discovered in the area of lab tests.
• Glucose, hemoglobin, urinalysis - these tests are measuring something in the sample
• 100g/ml - 100 grams glucose per ml of blood. This would be a finding on a glucose blood test.
• Lab tests should be utilized as an aid to clinical judgment
• The more you know about the patient the better off everyone is going to be
• Tests allow you to determine things that no other thing could find
• Conformation of Clinical impression - a hunch or guess that there is something wrong with the patient.
• Example - fasting glucose level for diabetes mellitus…should be lower than 126g/ml glucose blood level on 2 or more occasions, otherwise diabetes is present
▪ WHY? Did you think this - increased urination, weight loss, numbness in feet, feeling tired constantly
▪ Diabetes is a carbohydrate utilization problem.
• Example 2 - rheumatoid factor for rheumatoid arthritis
▪ Which causes which? Correlation? The autoimmune disease RA, is caused by the rheumatoid factor which is an antibody to and antibody
• Example 3 - Urine control for UTI (urgency, dysuria, constant urination)
• Example 4 - HbsAg for hepatitis B virus infection (looking at symptoms first to decide what to test for)
• Example 5 - Tropinin for MI (angina, tachycardia, cardiac injury, shortness of breath) all clinical signs, but tropinin test is used to see if MI has occurred
• Asking the right question can make the difference - you need to measure and look at the right thing. So your diagnosis is not any better than your diagnostic skills and information you have.
• Correlation - association between two things. If you know one thing you know something about the other, however it does not mean cause and effect (hyperglycemia and diabetes mellitus)
• Reduction of Differential diagnosis - trying to narrow down what is going on
• Example - do a serum amylase test to see if the person has (appendicitis, cholecystitis, and pancreatitis) These all show a sudden onset of acute abdominal pain.
▪ If amylase is high then it is pancreatitis. If not then you would look at the other 2. (correlation between amylase and pancreatitis, then depending on the elevation of the amylase in the blood the more damage that may be present)
• Biochemical marker - used to see the number of cells that are dead, and used to monitor progression or regression of necrotic tissue, just short of a biopsy (ex. Amylase test)
• Example 2 - do a plasma ACTH to determine if Cushing's syndrome or disease present. More common in females. You see weight in spare tire shape, puffy round face, easy bruise ability, facial hair, buffalo hump…she is becoming cushiode. Cushings disease = increased cortisol
• Syndrome - is looking like the disease, but it is not present. Could have adrenal or pituitary tumor. Could have cortisol shots. So is it an internal or external cause. Cortisol is elevated in both conditions, but primary adrenal will have decreased ACTH with symptoms.
• Disease - Cortisol high and ACTH high. (pituitary tumor)
Effective Laboratory Test Utilization
• ordering the correct test at the right time. This is the effective use of a lab test.
Disease Exclusion
• Normal glucose for hypoglycemia - you cannot tell someone what they have without confirming it. Blood tests for glucose…low blood glucose level…hypoglycemia.
• To correctly diagnosis this you must do Whipple's triad
▪ Classic symptoms of hypoglycemia
▪ Low glucose level, 50 or below during symptoms
▪ When given sugar during low BS, BS levels out and symptoms go away
• Normal hemoglobin for anemia - not due to shortage of red cells or hemoglobin
• Normal ALT/AST for Liver Necrosis - you think they have it because they are yellow or jaundice. This causes bilirubin level to build in the body. So they check for liver necrosis. (this will exclude hepatocellular necrosis when normal)
Indication for specific Therapy
• Iron
• Folate
• B-12
• Transfusion
• Surgery
Monitor Therapy for Effectiveness
• Sometime when you adjust or treat a patient, you need to have some sort of an outcome or expectation
• You should see if there are clinical improvements
• You find someone who has an elevated cholesterol, but you have to measure the hypercholesterolemia by Serum cholesterol
• Serum electrolytes for dehydration
• Serum albumin/protein for malnutrition
• Hemoglobin for anemia
• When taking antibiotics, people do not normally take all that is recommended. However, the bugs still exist. Then they get sick again. Doctors should have a test done when the treatment is complete to make sure everything is taken care of.
Disclose Occult Disease
• Something that can only be detected by diagnostic means . You cannot not visually see them or palpate them with the naked eye.
• The more you look for something the more likely you are able to find something.
• Full body MRI scan…scam…these are done on healthy people.
• Breast Cancer is an Occult disease, why…the more you look the more you find. People are finding bumps and lumps when doing a breast self exam.
• LOOKING for disease in healthy people bring up a lot of false positives…and that costs money. However, there are some like screening people for colon cancer, by looking for blood in the stool.
• There is a high correlation between colon cancer and the dried blood in the stool. There is a 75% to 80% pick up rate in colon cancer with the screening type test.
• What is the relationship? The tumor is outgrowing its blood supply and so the tumor bleeds and hemorrhages and dies.
Determination of baseline values
• To determine the patients normal values
• If we plot a normal bell curve you would find 95% of the people within a range however, 2.5% would be taller and 2.5% would be lower
• So if a person tests low when they are healthy and high er when they are sick, but still in the range, then it will be seen as a change and that number might not be normal for this patient.
• To establish a base line
• Weight, height, and so forth
• Severity of the disease
• Obese…700lbs and 900lbs and 300lbs
Staging
• Prodromal - incubation stage (hit your thumb…no pain yet, but its comin)
• Acute - the early stages (segmented neutrophils)
• Chronic - when the acute stage goes past a short time (monocytes)
• Convalescence - the healing phase or down side of illness
Defensive Chiropractic
• Malpractice - when your clinical knowledge is questioned in why you did not evaluate or test correctly
• Negligence - not paying attention to the signs of a problem, or not testing correctly
• Patient responsibilities - choosing to be responsible for a certain area of patient care. Depending on the area you focus you may not order certain tests.
Why do we order tests? - to answer questions
Laboratory results are physiological measurements
Laboratory test results require interpretation to have any meaning.
It is necessary to know normal values.
BP
175/110 mm/Hg
:(
HR
100/min
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Some values you know some you do not. Learn the chart that sanders gave out for normal values.
MEMORIZE SHEET!
Laboratory tests only indicate some qualitative or quantitative aspect of the patients sample at the time the sample was obtained.
A perfect test will identify all those patients with a specific sondition and exclude all those patients without a specific condition.
Test = a process of measuring something
Not all tests are perfect.
If a person test positive for a pregnancy test.
Male - could be a testicular tumor
Woman - could be pregnacy or hydatiform mole
• So is the person really pregnant?
• The presence of an embryo and a positive pregnancy test have a high correlation, but you are not measuring embryo. You are measuring HCG in the urine. This is why the test is not a guarantee.
If a person has glucose in their urine it is usually indicative of diabetes mellitus. However, this is not always the case. There is a rare disease called renal glycosuria where glucose would show positive in the urine.
Elevated WBCb
• Could be infection, inflammation, Shock, leukemia, variant
• It all depends on the correlation of things and then what is really present
Elevated Serum Creatine Phosphokinase
• Use this to measure muscle cells
• MI, Muscular dystrophy, tooth ache, post surgery, exercise
• Overall, muscle damage is present
• CPK is normally 25-250 IU
• 25,000 = surgery
• 2,500 = MI
• 500 = Muscular dystrophy or exercise
• 400 = Muscular dystrophy or exercise
• 252 = tooth ache
Postive test for rheumatoid factor
• Rheumatoid arthritis
• Subacute bacterial endocarditis
• Leprosy
• Sarcoidosis
• Hepatitis
• Normal ageing
What is Normal?
• Some people think that normal means there are no penalties
• However the bell shaped curve or parameter of findings, should not be the final thought or decision. The bell curve is just an average of the population.
• Abnormal - only means different
• Just because you are statistically different does not mean you are bad
• How about an abnormally high bank account
• With respect to lab value normals, we do not always know if normal is best or if normal is even good
• Cholesterol at 180-235 mg/dl
▪ Overall we want cholesterol to be below 200, but the above range is normal.
• Calcium 8.5 - 10.8 mg/dl
▪ What's better the low end or high end? Probably it would be better to have a high end since this would lower possible osteoporosis
• The numbers all come from statistics.
• All the numbers added up and then a standard deviation is scored. This range usually has about 95% of the people tested in it.
• Purely quantitative objective
• Creatin Kinase Values - CPK level is related to your muscle mass
• The point of this discussion…
• Disease Levels vs Health Levels
▪ There are levels that show definite disease and most likely healthly levels
• If you are outside of the range then people try to fix it.
• Population Demographics - different between people, usually it is caused by Body mass or hormones
• Gender
▪ Male - more testosterone, heavier,
• Age
▪ Are they young, old, baby, adult
• Ethnicity
• Analytic method - the technique we use will determine the outcome
• Reagents
• Procedures
• Temperatures
• Analytical Variable
▪ Sometimes you can have different numbers form the same test, but you want to consider the markers for high or low levels
• Reference interval - the area where people are normal the (95%)
▪ However how far over or under can someone go without being in a disease state?
Decision levels
• In order to make this decision correctly, for a given test, decision levels for that test must be established
▪ When does someone have scoliosis that needs treatment?
• There are a lot of factors that would go into theis to make the decision. How much worse has the patient got? Is it a quarter degree or 5 degrees
• These levels help you in distinguishing someone from the norm. So with the levels you can judge how far from the norm they are. The clinician also makes the call. There are usually no charts or defined guidelines on decision levels for everything.
▪ Diabetes - normal is 80-110 (if above 126 when fasting twice, person is diabetic)
▪ Cholesterol - if cholesterol is high then you risk for heart failure increases
▪ Anemia - (12-14 is reference value for a female) So will you treat a female if there hemoglobin is an 11? When there is more than a 1 gram drop you should check things out more
▪ Serum Enzyme changes - elevation of ALT (liver enzyme normally 5-35) when the high end number gets 2 times the high, that is when you should be concerned. So if someone has a 48, you are still ok, but at 70, you would want to investigate more. This is in an asymptomatic patient upon subjective and objective observation.
▪ Antibody titer changes - the amount of antibodies in your blood stream (ASO titer) this can vary but what level means what?
• So the last solution recorded is positive - this is when you continue to dilute the fluid. There has to be a four fold change in any titer before it means anything…The point is that there is no chart that can decide when something is significant or not. Everyone varies
Panic or Critical Alert value levels - these levels are so abnormal that they represent a threat to life. These lab results must be presented to the physician in an orderly yet timely manner. This means that they lab person will call your office and ask to talk to the doctor.
• Ca below 6 or above 12
• Hb below 6
• WBC below 3000
• pH to high or too low
• Platelet below 50,000
Diagnostic Value of a test
• In part, based on a reference ranges and in part , on the clinicians decision level or criteria, each test will have some power of predicting the presence or absence of a specific disease:
• The diagnostic value of a test result
Diagnostic Value of a Test Result
THE DIAGNOSTIC utility or accuracy of a laboratory test is defined by the tests
• The dx sensitivity and specificity should not be confused with the analytical sensitivity an specificity which will be discussed
• The sensitivity is the frequency of abnormal or positive test results in individuals who have a selected disease
• Percentage of true positive tests results in patients who have a disease you are looking for
• The specificity is the frequency with which a normal or negative test result is observed in individuals free of disease
• The predictive values - who should have it, how many?
• The efficiency or probability
• Sensitivity and specificity usually have an inverse relationship
• EX. A pregnancy test was developed that was supposed to be better than the other. 1000 females pregnant 900 not preg. And 100 preg.
▪ We got 90 positive on preg (true positive) and 10 neg.( false negative)
▪ On the non-preg, 180 preg (false postive) and 720 not preg.(true negative)
• Sensitivity 90%
• Specificity 80%
• Positive Predictive Value 33%
• Negative Predictive Value 99%
• Accuracy overall 81%
• However, there is a 98.6% chance of correctly identifying a female as not being pregnant.
• So, being that you need the negative to see if you are going to -ray, this is a good test for this reason. Yet if you are running a pregnancy clinic, this would be a poor test for finding positive pregnancies.
Elements of Laboratory test
Intraindividula variation - one factor not controllable by either physician or laboratory is the degree of normal diuranl, day to day, and seasonal variation in the concentrations of measured components in biological fluids
• Insulin
• Growth hormone
• ACTH and cortisol - can be a 50% difference in a 24 hr period (usually happens in the morning)
Preanalytical -
Analytical variation - this represents the lack of precision of the assay
Precision of a laboratory result refers to the reproducibility of a value
Postanalytical -
Accuracy - accuracy of a laboratory result refers to how close tohe result conform to the true value or concentration of the analayte
Accuracy - (+ or -) from the reading that could still be okay. This is looking at the degree of innacuracy.
Renal function in a diabetic:
There can be a 10% variation depending on the activity you do and what you eat.
Precision - how many times you can recreate the result
Accuracy - how close y
Importance?
Meaningful?
• What's associated with the number? Rick factor?
Case inpression
• These are important when in health center practicum
Sample Integrity
• A laboratory result is only as valid as the sample from which it was derived
• Blood specimens are most commonly procured via venipuncture using evacuated collection devices
• Serum (blood not circulating) specimens are obtained from plain evacuated tubes or tubes containing a separator gel
• When whole blood or plasma (circulated blood) is required a variety of anticogulant tubes used.
Sample integrity
• Heparin
• Oxalate/Fluoride
• Ethylenediaminetetraacetic acid (EDTA)
• Citrate
• Gel Separation Tubes
For each test there is usually a preferred sample. Some tests the preferred test is oxelate or citrate, and at other times it is heparin.
Oxalate removes Oxygen
EDTA is the optimal anticoagulant for hematology testing because it does not produce changes in erythrocyte volume,
Incorrect Sample
• When you send the wrong sample you will get weird results
• Serum for a Prothrombin Time - this is a test to determine the first phase of coagulation to form
CBC can be used for a baseline assessment or point in time values.
Formed elements
Hemoglobin, % hematocrit, and white cell differential
Sometimes an individual component of the CBC test can be ordered. In general though you are looking at a very specific condition.
Ordering the tests together will also help save money in the end.
RBC Count - the number of RBC's per unit volume is measured directly and given in millions per microliter
Hemoglobin (Hgb) - the Hgb is measured directly and given in grams per deciliter. This value, along with Hct, provides a…..
Hematocrit (Hct) - The percentage of red cells per unit of packed blood, 35 - 40 % is normally red cells
The more red cells you have the more hemoglobin you have
Hemoglobin is 1/3 the hematocrit. (15% hemoglobin = 45% hematocrit)
Red cell indices - these describe the size of the red cell
Mean Corpuscular Volume (MCV) = the average volume of a red cell and is the most important index for classification of anemias into "macrocytic" with higher than normal MCV and "microcytic" with low MCV
Mean Corpuscular Hemoglobin (MCH) = (Hgb / RBC count) and gives the average mass of Hgb in an individual RBC; the unit is a picogram
Mean Corpuscular Hemoglobin (MCHC) = the MCHC is calculated (Hgb/Hct)
An abnormally low platelet level (thrombocytopenia) may result from ...
Increased destruction of platelets
• Idiopathic thrombocytopenic purpura (ITP)
• Hypersplenism
Decreased production
• Aplasti anemia
Increased usage
• Disseminated intravascular coagulation (DIC)
Abnormally high platelet levels
• Benign rx to infection, surgery
WBC - colors show what is present in the cell
• Lysosmes - are secretory vesicles (basophiles have mistamine)
• Agranulocytes
Lymphocytes and monocytes have complete nucleus (mononuclear cells)
Basophils and eosinophils have segmented nucleus (SEGS)
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