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Understanding Your Lab Results
Terry Watnick, M.D. Division of Nephrology
The University of Maryland School of Medicine Baltimore, Maryland
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What you will Learn today: • Lab Results-The Basics • CBC: Complete Blood Count • “Kidney Labs” Basic Metabolic Panel • “Bone” Labs • Liver Function Studies • Lipid Profile
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Why Should you Understand your Lab Results?
• Many Decisions that your health provider makes are based on your lab tests – Establishing a diagnosis – Developing a course of action for treatment – Monitoring response to therapy
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What is in Blood?
• WBC: Cells that fight foreign bodies, infection
• RBC: Cells that carry oxygen • Plasma: Contains clotting factors,
fibrinogen • Serum: The part that remains after
fibrinogen is removed & blood clots – Water w/Dissolved proteins (hormones) – Minerals, C02, electrolytes
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Example Lab Report
http://labtestsonline.org/assets/static-pages/SampleReport.html
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“Panic Values”
Critical Results or those that are dangerously abnormal must be reported to the responsible person and the lab usually makes note of that
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What is meant by the Reference Range? • Normal range vs. Reference Range
– Established by testing a large population of healthy individuals. There is usually a range of “normal”.
– Medical data must be interpreted in context. – For example Avg. heart rate is 70, but in a runner 55 may be ok.
• Reference range interpreted in the context of the reference population.
– Reference Range may vary with Age, for example Alkaline Phosphatase made by bone is higher in kids.
– Reference Range may with Sex, for example creatinine tends to be higher in males
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What does it mean if my value is out of the Ref. Range? • Statistical Variability-same sample, ~5% may fall outside the
normal range by chance. • Biological Variability, may vary day to day. • Individual Variability: What is normal? HOWEVER values out of the Ref. Range: • May be significant or indicate a problem that warrants further
investigation. • Analyzed in context of your symptoms, physical exam etc • May need to be repeated:
• For the reasons above. • sample wasn’t collected properly ie not refrigerated, RBC not
separated from serum.
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Lab Results must be interpreted in Context by your Health Care Provider
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The Complete Blood Count or “CBC”
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CBC: Complete Blood Count-I
• Evaluates 3 cell types that circulate in the blood: – WBC (white blood cells) – RBC (red blood cells) – Platelets
• Screens for wide variety of conditions – Infection – Anemia – Inflammation – Bleeding Disorder
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CBC: Complete Blood Count-II
• WBC (ref range: 4-11K) – Fight Infection, WBC goes up
when there is a bacterial infection – Differential: Major types of WBC:
neutrophils, lymphocytes – Each type of WBC plays a different
role in the body and the numbers give information about the immune system
• Ex. Eosinophils allergic reactions
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CBC: Complete Blood Count-III • Red Blood Cell Count (RBC, ref range 4.1-5.6)
– RBC carry oxygen from the lungs, CO2 from body to lungs • Hemoglobin (12.5-17) is the protein in RBC that carries 02 • Hematocrit (packed cell volume, ref. 36-50%)
– Volume of blood taken up by red cells
• Hemoglobin /Hematocrit are best measures of Anemia • Red Cell Indices
– Mean corpuscular volume (MCV) – Mean corpuscular hemoglobin (MCH) – Mean Corpuscular hemoglobin concentration (MCHC)
• Platelets ( ref range 140K-415K), required for clotting – Too few can cause bleeding, too many clotting
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WBC • Decrease
– Bone marrow, disorders or damage
– Autoimmune (SLE), diseases of immune system, HIV
– Sepsis -overwhelming infection – Cancer that spreads to the
bone marrow • Increase
– Infection, bacterial or viral – Inflammation – Leukemia – Severe Stress – Steroids
Platelet • Decrease
(thrombocytopenia) – Viral infection, hepatitis, mono – Platelet autoantibody,
autoimmune – Cirrhosis – Sepsis – Leukemia, other bone marrow
disorders – Chemo, XRT
• Increase – Malignancy – Iron deficiency – RA, SLE, IBD – Essential thrombocytosis
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Many Causes of Anemia • Acute or Chronic Bleeding • Nutritional Deficiencies: Iron,
B12, folate • Inherited: sickle cell,
thalassemia • Bone marrow disorders • Chronic Inflammation: lupus,
infection • Viral: hepatitis, HIV • Any Chronic Disease-renal
failure • Drugs: chemotherapy
Polycythemia • Dehydration • Lung Disease, smoking
emphysema • Tumors that produce extra
EPO • Polycythemia Vera
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Anemia in Renal Disease • Low RBC/low hemoglobin/low
hematocrit=anemia – Red blood cells carry oxygen to tissues
• Anemia is common in renal disease – Can occur early: 20-50% function remains – Kidneys make erythropoietin (EPO),
stimulates bone marrow – Diseased kidneys don’t make enough EPO
• Treatment – Recombinant EPO, subcutaneously, may
also need iron – Target hemoglobin 10-12, must be
monitored
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Functions of the Kidney • Two kidneys, either side of spine. • Each Kidney: 1 million nephrons.
– Nephron filters/processes blood to form urine.
• Regulates the amount of fluid and electrolytes: potassium, calcium & magnesium.
• Waste products ie creatinine are also filtered.
• Kidneys produces 3 hormones: – Erythropoietin, ensures that red blood cells
are produced. – Renin, regulates blood pressure. – Active form of Vitamin ensures calcium is
absorbed from food that we eat.
http://www.nlm.nih.gov/medlineplus/ency/imagepages/19615.htm
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Basic/Comprehensive Metabolic Panel
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Electrolytes (Na+, K+, Cl-, HC03-)
• Electrolyte Levels are Affected by – How much you take in. – The amount of water in your body. – How much you excrete: The kidney is critical in regulating
how you excrete electrolytes. – You can also lose electrolytes in stool and sweat. – Aldosterone, a hormone produced by the adrenal gland
promotes sodium reabsorption, potassium and hydrogen ion excretion by the kidney.
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Sodium, Na+ (ref range: 135-145) • Major positive ion in fluid outside of cells • Brain, muscles, nervous system depend on electrical signals
– Movement of Na+ is critical for electrical signals. – Too much or too little causes cells to malfunction. – Extremes in Na+ levels (too much or too little) can be fatal.
• Excess Na+ such as that in the diet is excreted by the kidneys – Na+ regulates the total amount of fluid in the body.
• Low Na+ or Hyponatremia – Excess water in relation to Na+. – Diseases of the liver, cirrhosis or congestive heart failure. – Excess water drinking.
• High Na+ or Hypernatremia – Excess Na+ in relation to water. – Too little water intake, Loss of water ie vomiting or diarrhea.
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Giebisch G, et al, Kidney Int 72: 397-410, 2007
Potassium (ref range: 3.5-5 meq/L)
• Major positive ion inside cells. • Potassium is found in many foods. • Potassium is mostly excreted by
the kidney (~90%). • Potassium is excreted by the GI
tract ~10% under normal conditions.
• Small amount in Sweat. • Aldosterone is a hormone made
by the adrenal gland that is very important in regulating K+ excretion by the kidney.
10%
90%
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Why is the Potassium level important? • Proper level is important for normal cell function
– Regulates heart beat and muscle function • Serious Increase aka hyperkalemia or Serious decrease aka
hypokalemia – Increase the chance of irregular heart beat that can be fatal
• The Kidney is critical for getting rid of excess potassium – Small amounts in stool and sweat
• If it is <3.5……………………………You are in the Low Zone If it is 3.5-5.0………………………You are in the SAFE zoneIf it is 5.1-6.0………………………You are in the CAUTION zoneIf it is higher than 6.0……………..You are in the DANGER zone
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Abnormal Potassium Too High • Increased Intake, supplements • Kidney Failure • Acid level high • Tissue Trauma
– rhabdomyolysis-muscle breakdown
• Not Enough Aldosterone – Adrenal Failure
• Drugs – Angiotensin-converting enzyme
inhibitors “ACE” – Certain Diuretics (aldactone,
triamterene) – Bactrim
Too Low • Poor Intake • Loss from GI tract
– Vomiting, diarrhea – Excessive laxative use
• Diuretics – HCTZ, Lasix
• Excess aldosterone • Excessive Sweating
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Other Electrolytes: Chloride/Bicarbonate Chloride: Cl-
• Ordered with other electrolytes as part of a panel.
• Helps in the diagnosis of other electrolyte abnormalities.
• Can be high in dehydration. • Can be high when too much
bicarbonate is lost. – Can be elevated with
diarrhea
Bicarbonate: or total C02 • Reflects Acid-Base Balance • Bicarbonate= Acid low
– Severe vomiting – Lung Disease (emphysema) – Severe Dehydration – Increased Aldosterone
• Bicarbonate = Acid High – Renal failure (Can’t excrete) – Diabetic ketoacidosis – Chronic diarrhea – Salicylate, methanol, ethylene
glycol – Decreased aldosterone
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Basic/Comprehensive Metabolic Panel
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What is Glomerular Filtration Rate or GFR? • How well the kidneys are
working: The volume of filtrate produced per minute.
• Normally Kidneys filter 180 Liters of blood per day.
• Only 1-2 Liters of urine. • 99% reabsorbed into blood. • Composition of urine
modified by secretion/reabsorption.
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How do we determine Renal Function or GFR? In Clinical Practice the plasma concentrations of waste substances such as creatinine and urea (BUN) are used to estimate renal function.
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Measurements of Renal Function, BUN
• Blood Urea Nitrogen or BUN (Reference Range: 6-24). • Urea is produced in the liver when protein is broken
down to amino acids. • Urea released into the blood where it is filtered and
excreted by the kidneys. • Conditions that affect the kidneys and or liver can affect
the amount of urea in the blood. • A High BUN implies impaired Kidney function
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BUT BUN can be elevated for reasons other than kidney damage
– Any condition that results in decreased blood flow to the kidneys such as congestive heart failure.
– Severe Dehydration – GI bleeding – Increased Catabolism or protein breakdown
• Increased Protein in the diet • Steroids such as prednisone
– Low BUN not usually a cause for concern can be seen in severe liver disease or malnutrition
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Other Measurements of Renal Function
• Creatinine is the best measure of renal function: – Reference range: 0.7 to 1.3 mg/dL for men and 0.6
to 1.1 for women • Muscular young adults may have more, elderly less
– Produced continuously from muscle breakdown – Kidneys filter creatinine from blood into the urine – Amount of blood that is cleared of creatinine each
minute is called the creatinine clearance. – Creatinine clearance is a good approximation of
the glomerular filtration rate or GFR
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Can we estimate GFR from Creatinine?
• YES! Glomerular Filtration Rate can be estimated from serum creatinine measurements.
• Calculated using the Modification of Diet in Renal Disease Equation MDRD, referred to as eGFR.
• GFR (mL/min/1.73 m2) = 175 × (Scr)-1.154 × (Age)-0.203 × (0.742 if female) × (1.212 if African American).
• Takes into account, gender, age, race. • Most thoroughly validated equation
– Caucasians, African Americans ages 18-70 w/GFR< 60
• More useful than creatinine alone, why?
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Same creatinine: Very Different GFR
http://www.kidney.org/professionals/kls/pdf/12-10-4004_KBB_FAQs_AboutGFR-1.pdf
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Limitations of eGFR: Still an estimate • Not for non-adults • Patients with extremes in muscle
mass or diet – Taking supplements – Obese, amputees
• Creatinine must be stable – Not in pregnancy – Acute illness, hospitalized patients – Acute Kidney Injury
• Will under estimate kidney function in those with near normal function
• Captures only some non-GFR determinants of creatinine
Estimated GFR ml/min/1.73 m2
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Levey and Stevens, Frequently Asked Questions About GFR Estimates, copyright National Kidney Foundation, 2004.
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Other Methods for Measuring GFR
• CKD-EPI equation – May be more accurate at higher kidney function GFRs – Not as well validated as MDRD
• 24 hr urine collection for creatinine, simultaneous blood Cr, UV/P1440 – Over estimate at low GFRs, eGFR using MDRD is more accurate – Relies on accurate collections, may need to repeat multiple times – Can be useful when eGFRs suspected to be inaccurate
• Inulin, iothalamte, iohexol Clearances – These may be accurate but they are research tools
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Stages of Chronic Kidney Disease (CKD)
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Urinalysis
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Urinalysis
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Proteinuria: Protein in the urine • Protein in the urine/proteinuria may
be the first sign of kidney disease • Can be measured by dip stick or urine
albumin/creatinine ratio. • >30mg/g abnormal • 30-300 mg/g microalbuminuria • >300 mg/g macroalbuminuria • 24 hour urine collection: >3g/24h
considered to be nephrotic range • ADPKD is not usually associated with
nephrotic range proteinuria
Glomerular ultrafiltrate should not contain protein
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Basic/Comprehensive Metabolic Panel
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Why Bone? • When the Kidney isn’t
working (Stage3-4): – Phosphate: – Active form of Vitamin D:
• This results in lower calcium • Signals to the parathyroid
gland to make more PTH. • This causes bone disease. • Your Doctor may check your
Intact PTH level • Rx: Active form of 1, 25
VitaminD
Ref Ranges: Calcium (8.7-10.2) Phosphorus (2.5-4.5)
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Liver Function Tests LFTs
• Purpose to monitor liver disease or function • ALT and AST: Enzymes found in the liver cells used to detect liver damage
ie from hepatitis, drugs • Alkaline phosphatase: produced by bile ducts and rises when this is
blocked. Also made by bone, intestine. • Bilirubin: Break down product of red blood cells, modified in the liver,
secreted in bile and urine. Elevated levels cause jaundice • Albumin is a protein made by the liver, binds to hormones, proteins in the
blood
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Fasting Lipid Profile (9-12 hours)
• Two types of Lipids transported in blood, cholesterol and Triglycerides, by particles containing different fats and protein (lipoprotein particles).
• Total cholesterol measures all types of cholesterol in these particles. • HDL or “good cholesterol” : excess cholesterol to the liver for removal. • LDL or “bad cholesterol”: Deposits in blood vessels. • Lipid Profile: part of a cardiac risk assessment-risk of heart disease • Treatment depends on the results and other risk factors. • May include life style changes ie diet and exercise, medications.
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Questions???
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Helpful References
• National Kidney Disease Education Program: http://nkdep.nih.gov/index.shtml
• Lab Tests On Line: http://labtestsonline.org/understanding/ • National Kidney Foundation: Frequently asked questions about GFR:
http://www.kidney.org/professionals/kdoqi/gfr.cfm • National Kidney and Urologic Diseases Information Clearing House
(NKUDIC): http://kidney.niddk.nih.gov/index.aspx • GFR
Calculator:http://www.kidney.org/professionals/kdoqi/gfr_calculator.cfm
• Kidney Function: http://humanphysiology2011.wikispaces.com/12.+Urology