Lab Diagnosis: Midterm Review
CALCULATED BLOOD values:
HCT = hematocrit = MCV x #RBC / 10
MCV = mean corpuscular volume = Hct% x 10 / millions RBC's
MCH = mean corp hemoglobin = Hgb x 10 / millions RBC's
MCHC = mean corp hemoglobin concentration = Hgb (g/dl) x 100 / Hct %
RI =
MEASURED:
RBC
RDW
Retic
1. Why do we do lab measurements? Baseline. Diasnosis. Rule out. Follow progress. Recognize secondary disease. Get feedback during course of treatment. Hx & PE-->DDX-->proper test. Pancreatitis: lipase. Perforated ulcer: Hgb. UTI: UA. Ectopic preg: HCG. Appendicitis: WBC. Cholestastis: bilirubin.
Normal range = determined by lab for its equipment on the pop it tested
Prevalence = # people who currently have condition
Incidence = # who annually have the condition in a year, only new not pre-existing
True postitive = has dz, was identified as such
True negative = not dzd, id'd as such
Precision = reproducibility, better with small SD's
Accuracy =
Sensitivity = true positives/all diseased, ability of test to detect pts who have dz, true positive value (gives false neg rate?)
Specificity = true negatives/not diseased, ability of test to detect pts who do not have dz, true negative value
False positive = not dzd but test was positive
False negative = dzd but test was negative
PPV = positive predictive value = % of positives that are true, those w/ dz and test pos/all who test pos, 100% minutes this percentage gives false positive rate
NPV = negative predictive value = % of negatives that are true, those w/o dz and test neg/all who test neg, 100% minus this percentage gives false negative rate
2. Understand potential problems with lab tests. Microclots in blood. Clean catch for urine. Large enough sample of stool. Hair from new growth not old. Specimen mixing. Aliquot representativeness. Machinery tuning. Tech training. Patient condition. Drug interactions. Time of day. Fasting or not. Hydration state. Stress. Hunger. Body position. Snapshot in time. Also: Risk/benefit ratio, similarities of tests, cost, invasiveness.
Give general rules for handling expected and unexpected lab results. Present results to pt in professional manner. Recognize life threats. Document on chart. Be culturally sensitive. Offer support as needed. If Unexpected: repeat test on same sample and new sample. Split sample and send to different labs. Consult with lab pathologist. Consult with other professionals. Revisit pt hx and take more hx if needed. Look it up.
3. Calculate (bring calculator!):
specificity = true neg / no dz
sensitivity = true pos / dz
PPV = true pos / pos
NPV = true neg / neg
false neg = 100% - NPV
false pos = 100% - PPV
URINALYSIS
1. Review normal kidney fx. How much urine is produced daily? 1,000-1,800 ml/day, PCT's add secretions to filtrate, concentration happens in loop of henle, DCT and collecting ducts, urine formation influenced by BP, ADH, acid-base balance, fluid balance, nutrient intake
2. Know the 3 components of routine urinalysis: physical (color, clarity, odor), chemical/dipstick (gluc, bili, ketone, SG, leukocyte esterase, urobili, prot, pH, nitrite, blood), microscopic (epithelial cells, crystals, WBC's, RBC's, casts, bacteria, misc: feces, sperm)
color: urochrome makes normal color, red: hematuria dt kidney or UTI bleed, very pale dt overhydration, DM, DI, diuretics, clear red dt beets/rhubarb, dark amber/brown dt carrots/cascara, bright yellow dt riboflavin, green dt pseudomonas/biliverdin, orange dt pryidium/carrots, port wine color dt hemoglobinuria, myoglobinuria, porphyria, black dt melanin, alkaptonuria, RBC's oxidized to methemoglobin, other drugs also.
cloudy dt WVC's, bacteria, amorphous acidic urates, amorphos alkaline phosphates, epithelia cells, hyperuricosuria (purines), hazy dt all of the above plus mucus/protein, milky dt fat, lipids, smoky dt RBC's
odor: ammonia dt urea splitting bact, sweet/fruity dt ketones, maply dt maple syrup urine dz, musty/mousy dt phenylketonuria, sulfury dt asparagus, fruity/grape dt pseudomonas
SG normal: 1.010-1.025
--over 1.025 = hypersthenuria
--increased SG can be caused by nephrotic syndrom, drugs, dehydration, SIADH, CHF, pregnancy,
--decreased SG can be caused by overhydration, chronic renal dz, DI (insuff ADH), diuretics, glomerulonephritis
--isosthenuria = SG not change because kidneys not concentrating urine
--high false pos dt proteinuria
--low false pos dt very alkaline urine on bayer dipsticks
pH
Acidic urine: consider UTI w/ E. Coli, DM, acidosis, COPD, diet high in meat, cranberries
Alkaline urine: consider UTI w/ Proteus, Pseudomonas, also alkalosis, gastric suction, vomiting, renal tubular acidosis, vegetarian diet, high citrus intake
Urobilinogen
--elevated due to intestinal obstuction??
--acute hep early stage
Nitrites
--if pos look for gram neg bact infx
Protein
--sensitive indicator of kidney fx, should be no prots in urine
--increases dt: renal dz, trauma, macroblobulinemia & multiple myeloma, pre-eclampsia, eclampsia, CHF, orthostatic proteinuria, hard workout, renal vein thrombosis, bladder tumor, urethritis or prostatitis, amyloidosis, etc. Can be transient but anything over 1+ or 30mg/dl is SIGNIFICANT.
Leukocyte esterase
--positive suggests UTI, but can mean appendicitis or pancreatitis!!!
Crystals: UTI w/ proteus-->triple phosphate crystals, special TX.
3. Give reasons for false positives and negatives on dipstick.
--Vit C causes 4 false negatives: GBBN: gluc, bili, blood, nitrites
--Vit C causes 1 false positive: WBC's
--LIGHT degrates pigments
--GLUCOSE can cause false neg of leukocyte esterase
--bilirubin false negs dt: vit c, nitrites, light
--bili false pos dt fecal, pyridium indican
--ketone false pos dt levodopa, phynyketones, phthaleins, high pigments
--ketone false neg dt air exposure
--blood false pos: myoglobinuria, menstrual, oxidizers, microbial peroxidases
--blood false neg: vit c, nitrites, captopril, high SG
--protein false pos: vaginal, hematuria, alkaline, pyridium
--protein false neg: dilute, or other proteins incl: globulins, glycoprots, bence-jones prots
--urobilinogen false pos: fecal, drugs, beets
--urobilinogen false neg: antibiotics, oxidation dt standing too long, formaldehyde
--nitrites false pos: pyridium, beets, old sample
--nitrites false neg: vit c, low nitrate diet, high SG, urine in bladder over 4 hours
--leukocyte esterase false pos: deep yellow pigments and oxidizing detergents
--leuko false neg: GLUCOSE, PROTEIN, HIGH SG, oxalates, some Abx
4. Be able to correlate abnormal results with urinary tract pathology and patient's presentation.
Yes ma'am.
5. Where is glucose reabsorbed? proximal tubule
What is the renal threshhold for glucose? 160mg/ml?dl? serum
6. Which form of bilirubin is water soluble?
conjugated (w/ glucuronic a.)->secreted by hepatocytes into bile
Which requires carrier protein? unconjugated bilirubin
7. Know hemoglobinuria vs hematuria. Yep. Uria = in urine. hemat = blood.
Which will show intact cells on microscopic exam? Hematuria.
8. Where & under what pH are casts created?
What do they signify? Which are pathognomic for what?
--WBC casts suggest infectious or inflam dz of kidney: acute pyelonephritis, glomerulonephritis, lupus nephritis; appear in in acidic and concentrated urine, assoc with proteinuria and urinary stasis, dissolve in alkaline
--RBC casts are pathological, bleed in kidney, pathognomic for glomerulonephritis, can suggest SBE, renal infarct, vasculitis, sickle cell anemia, SLE, malignant hypertension, Goodpasture's syndrome
--renal failure casts also known as waxy or broad casts, are degenerated granular casts, sign of chronic destructive renal dz
--"WBC cast = interstitial nephritis, pyelo"nephritis".... just as in the slide" --Dr Wiggin
SBE = subacute bacterial endocarditis
OTHER CASTS NOT MENTIONED IN Q
--Tamm-horsefall prot is a globulin thus NOT detected on dipstick, secreted due to stasis
--hyaline casts are chronic, indicate glomerulonephritis, pyelonephritis, CHF, CRF
--renal tubular epithelial cell casts follow dz that damages tubule epithelium, incl: nephrosis, amyloidosis, heavy metal poisoning, glomerulonephritis, acute tubular necrosis, pyelonephritis
--granular casts are degenerated cellular casts that turn into waxy/broad casts
--fatty casts seen in chronic renal dz
RENAL FUNCTION TESTS
1. Understand these tests for evaluating renal blood flow, glomerular function and GRF, rental tubule fx.
--BUN = blood urea nitrogen, evaluates liver fx, BUN is filtered by glomerulus, 40% is reabsorbed, is about 60% of GFR in most conditions (indirect measure, rough indicator of GFR and renal blood flow), OVER 100 means serious impairment of renal fx, normal is 10-20 mg/dl, slightly higher in elders, azotemia is increased BUN
--creatinine = a catabolic product of creatine phosphate from skeletal muscle, depends on muscle mass, is filtered in glomerulus and excreted in PCT completely unless kidney probs, serum levels raise later than BUN, doubling of serum creatinine suggests a 50% reduction in GFR
--creatinine clearance = comparison of serum and urine levels to evaluate kidney fx, need 24 hour urine collection and blood draw, correct for body weight and height, GOOD ESTIMATE OF GFR until it's 30% or lower, elevated by exercise, preg, increased CO, decreased by lowered GFR
--fractional excretion of sodium (FENa) = compares urine Na and creatine with plasma Na and creatine, discriminates pre-renal (FENa under 1%) from renal azotemia (FENa 2%) because tubules can't conserve Na.
2. Know the significance of clearance tests & tubular function tests.
--most important indicator of renal dz is proteinuria, over 3500mg/24hrs means nephrotic syndrome
3. Distinguish between pre-renal, renal and post-renal azotemia.
pre-renal: 55% dt dehydratione, CHF, MI, GI bleed, too much prot intake, starvation, sepsis
renal: 40% dt renal dz, renal failure, nephrotoxic drugs
post renal: 5% dt obstruction of ureters or bladder outlet dt stones, tumors esp prostate, congenital
4. Know the differences between acute and chronic renal failure
acute: ARF: hx of normal renal fx, kidney size normal, no broad casts, usu no anemia
chronic: CRF: gradual deterioration, hx of increased BUN & creatinine, kidnesy usu small, anemia oft present, broad casts in urine seidment
5. Know ALL the components of testing for 24 hour CCLR and what measurement the test provides us with.
--urine creat/serum creat x 24hrs/1440mins x meterssquared/1.73msquared x volume(ml) = ??
--normal: male: 90-139 ml/min, female: 80-125 ml/min
--value decreases 6.5ml/min for each decade after age 20 dt decline in GFR
--creatinine clearance tells us how well the kidneys are filtering out creatinine from the blood, it all should go
6. What is the most important indicator of renal dz?
PROTEINURIA
7. What clinical dz is the 24 hour urinary calcium most used to detect?
HYPERCALCEMIA dt hyperparathyroidism or other, can cause recurrent nephrolithiasis (stones, bones, groans, moans, psych overtones--kidney stones, pain in bones, abdominal moans/groans, psych overtones of fatigue and depression). diet can interfere, alkaline urine causes decrease in detection, immobilization releases Ca from bones, drugs change results too
8. What 3 catecholamines are we following when we test the primary end products HVA and VMA in urine? And what can they be used to dx?
--dopamine, norepinephrine, epinephrine
--used to Dx: pheochromocytoma, neuroblastoma, ganglioneuroma, ganglioneuroblastoma, rare adrenal tumors
9. Which bone turnover lab test is best?
The deoxypyridinoline test is cheaper and less specific (best?)
The NTX test, N-telopeptide test, is more specific for bone but perhaps not necessary.
"Slide #43 specifically states: NTx more specific for bone than deoxypyridinoline" = best per Dr Wiggin.
10. Evaluation of what potential pathologies is beta HCG used to determine? ectopic preg, hydatidiform mole, choriocarcinoma
How soon is it detectable in prenancy? 10 days after conception
Where does it come from? placental trophoblast
COMPLETE BLOOD COUNT
1. Know RBC function and significance of decreased/increased values.
--fx: uses hemoglobin to carry O2, CO2, live and circulate 120 days, buffer blood pH w/ carbonic anhydrase
--recycled in spleen and liver
--RBC normals: men: 4.7-6.1, women 4.2-5.4, newborn 4.8-7.1, sometimes as low as 3.5 under 1 year
--increased number RBC: ??? polycythemia vera
--decreased number RBC: anemia (iron deficiency, macrocytic, hemolytic)
--decreasing factors: preg, nutrit prob, hydrate, chlorampheincol, quinidine
--increasing factors: altitutde, dehydrate, gentamycin, methyldopa
--MCV = mean cell volume
--Coulter method measures RBC#, MCV, Hmg. Hct is CALCULATED. Does not report shape/color/density.
2. Know definition, what they tell about RBC pop, what clinical correlations are there?
anisocytosis = variation in RBC SIZE
poikilocytosis = extreme variation in RBC SHAPE
RDW = RBC distribution width, significant when elevated because it tells you cell size is variable or changing
3. Know primary diseases to consider for the following RBC morphologies:
target cell = from thalassemia, liver dz, abnormal hemoglobin
drepanocyte = sickle or crescent shaped RBC's dt sickle cell anemia
elliptocyte = hereditary elliptocytosis, sickle cell anemia
spherocyte = hereditary, autoimmune hemolytic anemia, thermal injury, physical injury (artificial heart valves) toxins (snake venom)
schistocyte = burr cell dt uremia, liver dz, hyperlipidemia, artifact
degmacyte
4. Know the significance of these RBC inclusions:
--Howell-Jolly bodies = hello dolly = DNA = B12 deficient, severe hemolytic anemia, thalassemia, splenectomy
--Heinz bodies = denatured Hgb, could be congenital glucose-6-phosphate deficiency, drug-induced hemolytic anemia, unstable abnormal hemoglobins. Test pt for G6PD before giving high vitamin C doses in cancer tx. fava beans?
--basophilic stippling = common, purple/blue particles of precipitated RNA due to heavy metal poisoning, (esp lead), severe bacterial infx or drug rxn
5. Reticulocytes: know etiology, which hormone stimulates maturation, and the reason for the use of reticulocyte index.
Retic = immature and anucleate RBC wtih reticular material containing RNA
retic count indicates bone marrow function
hormone that stimulates maturation: erythropoetin, from kidneys???
reticulocyte index = to evaluate reticulocyte count with respect to patient's hematocrit. RI = (retic%/pt'sHct)/normalHct.
6. Know definition of ESR, Erythrocyte sedimentation rate, and understand test setup
ERS = erythrocyte sedimentation rate in a saline solution, one hour in mm/hour, nonspecific test useful to detect actue or chronic infections, inflam, collagen-vascular dz = autoimmune dz, invasive neoplasm, tissue necrosis, tissue infarction
test setup: little tubes stood vertically, keep away from vibration, no bubbles, saline solution, one hour
zeta potential = negative charge on RBC's that keeps them from stacking too close, can be neutralized by acute phase reactants such as fibrinogen, won't stack if shaped funny
roleaux = rollo RBC's when zeta potential is overwhelmed and cells stack, adding up to an increased sed rate
interfering factors = low results if old sample (need under 3 hours), pregnancy (2-3rd trimester can elevate), menstruation (up), some anemias falsely increase, polycythemia and sickle cell dz decreases, protein-producing malignancies increase, any BUBBLE in column invalidates
validating factors = ??
What do you mean by "validating factors" when you refer to ESR? see slide #47
OK, slide #47 lists the INTERFERING FACTORS:
Low if:
--test not set up w/in 3 hours of sample collection
--polycythemia or sickle cell anemia
High if:
--pregnant (2nd & 3rd trimester)
--menstruation
--some anemias (correction nomograms available)
--protein-producing malignancies
--vibration during settling increases sed rate
Off if:
--sedimentation tube not vertical
--invalid if bubble in tube
increased ESR: chronic renal failure, malignancy, bact infx, inflam/autoimmune, necrotic dz, MI, dz assoc w/ inc plasma prots, "VERY useful to Dz polymyalgia rheumatica and temporal arteritis (may be over 100 mm/hr)"
falsely decreased ESR dt sickle cell, hereditary spherocytosis, hypofibrinogenemia, polycythemia vera
polycythemia vera = bone marrow makes too many RBC's, WBC's and platelets, etio: unknown, tx: leeches
HGB, HEMATOCRIT, RBC INDICES, PORPHYRIAS, THALASSEMIA, ANEMIA
1. Know heme and globin synthesis
hemoglobin structure = tetrameric, four heme groups, metallo-porphyrin ring, iron and red pigment, binds O2 and CO2 and CO and others, globin is made of four aa chains, 2 alpha and 2 beta
Normal types of hemoglobin:
--HbA1 (97%) A1 = alpha-beta
--HbA2 (2%) A2 = alpha-delta
--HbF (1%) fetal = alpha-gamma
--Alpha from chromosome 16 and beta
--delta and gamma chains from chromosome 11
Abnormal hemoglobins:
--HbS (sickle cell anemia)
--HbC (results in mild hemolytic anemia)
--most common abnormality is increase in HbA2, which is diagnostic of thalassemia esp Beta-thalassemia trait.
--more than 250 variants of Hb have been recognized.
How does lead interfere? In 7 step heme synthesis process it inhibits a bone marrow enzyme (#2): ALAD = delta-aminolevulinic acid dehydratase, which stops heme synthesis, accumulated precursor is hepatocarcinogenic also blocks a later enzyme (#7, protoporphyrinogen oxidase, ferrochetalase). Visible basophilic stippling. (if ALAD is blocked, precursor accumulates and causes liver cancer)
2. Identify lab screening for hemoglobinopathies:
--screen for Hgb distribution using Hgb Electrophoresis
Normal hemoglobin values:
--meaured in g/dL
--spectophotometer lyses RBC's into hemoslysate which is read by shining light through it
--normal for males is 14.0-17.4g/dL
--normal for females 12-16
--normal for children variable: newborn has 50%-90% HbF that decreases to under 5% by 6 mo
Abnormal hemoglobins:
--HbF in adult more than 1% suggests thalassemia
--HbS = sickle
--HbC = dz in 3% of African Americans, results in mild hemolytic anemia
FROM BOOK NOT NOTES: MORE ABNORMALS:
--HgM = methemoglobin, ferric form of iron can't bind oxygen-->anoxia, cyanosis, 30% causes headaches, 70% death
--Sulfhemoglobin = abnormal pigment formed by combo w/ sulfides, oft with drug induced HgM, also causes cyanosis
--Carboxyhemoglobin - bound to CO2, Hb affinity for CO 240x greater than for O2
--Haptoglobin = a tgransport glycoprotein synthesized in liver, carried free Hb in plasma, preserves iron, if decreased indicates intravascular hemolysis
--Bart's Hgb = unstable w/ high O2 affinity, hereditary homozygous thalassemia from heterozygous parents, stillborn or dies soon after birth
Interpretation of abnormal hemoglobin values:
--over 16-17: high
--under 12-14: low
--depends on gender, men usu have more, also postmenopausal women
Factors that interfere with measurement of hemoglobin:
DECREASED due to
--low RBC production
--high RBC destruction
--hemorrhage
--increased blood volume (preg 1st trimester, overhydrated)
INCREASED due to
--increased RBC production
--dehydration
3. Know definition of hematocrit:
THE VOLUME OF ERYTHROCYTES EXPRESSED AS A PERCENTAGE OF THE VOLUME OF WHOLE BLOOD.
Relationship with RBC size and number:
--Indirect measure of RBC number and volume, directly related
--The rule of 3: Hct is approx 3x Hgb value when RBC's are normal size & Hgb content
Interpretation of abnormal hematocrit values
NORMAL: male 42-52%, female 36-46%, less in elders, kids variable, can go as high as 60%
INCREASED
--erythrocytosis
--congenital heart dz
--polycythemia vera (PCV)
--severe dehydration
--severe COPD
DECREASED
--anemia
--hemoglobinopathy
--cirrhosis
--hemolytic anemia
--hemorrhage
--nutrient deficiencies (iron, B12/folate)
--bone marrow failure
--prosthetic heart valves
--renal dz (no erythropoetin)
--normal preg: 1st trimester
--rhematoid/collagen vascular dz
--blood cancer/malignancy
Factors that interfere:
--RBC size: large RBC's higher % of blood volume-->higher Hct
--very high WBC count (false decrease)
--hydration state
--pregnancy (decrease dt hemodilution in 1st trimester)
--high altitude (increase dt hypoxia)
--post hemorrhage values not reliable
--drugs may decrease (chloramphenical, penicillin)
4. RBC indices
--MCV = mean corpuscular volume, ie size of RBC's reported in fL, femtoliters, normal is 82-97
--MCV (fL) = (HEMATOCRIT% x 10) / #RBC's in millions (CALCULATED)
--MCV: if decreased->microcytic RBC's, if increased->macrocytic
--MCH: AVERAGE WEIGHT OF HGB IN A RBC REPORTED IN PG, picograms, value follows MCV
--MCH = (HEMOGLOBIN x 10)/ RBC's in millions (CALCULATED)
Define and calculate mean corpuscular hemoglobin concentration
--MCHC = Hemoglogbin concentration of RBC's
--MCHC = weight to volume ratio of average concentration of Hgb in given volume of RBC's
--CALCULATED
--reported in g/dL
--Normal MCHC = 32-36 normochromic
--under 30 is hypochromic, low hgb content
--MCHC = (Hgb x 100) / Hct = (Hgb x 100) / (MCV x RBC) / 10 = (hgb x 100 x 10) / (MCV x RBC)
--theoretical limit of THIRTY SEVEN 37 !!! may read over 37 w/ spherocytosis, etc, then order a "manual"
Clinical interpretation and application of abnormal RBC indices in classifying anemia
--MCHC is used to help classify type of anemia
--anemia with normal MCHC is "normochromic anemia"
NORMOCYTIC NORMOCHROMIC ANEMIA
--early iron deficiency
--chronic illness (anemia of chronic dz)
--oft renal dz
--acute blood loss
--aplastic anemia (chem exposure)
--acquired hemolytic anemia
MICROCYTIC, HYPOCHROMIC ANEMIA (microhypo)
--iron deficiency
--thalassemia
--lead poisoning
--some texts put anemia of chronic dz here
MACROCYTIC NORMOCHROMIC ANEMIA
--vit B12/folic deficiency
--SE of chemo
--myelodysplastic syndrome (BM abnormality resulting in decreased prod of RBC/WBC's OR precursor to development of ACUTE MYELOGENOUS LEUKEMIA, aka AML, as much as 30%)
5. Know which thalassemia is most common and be able to differentiate between minor & major
--thalassemia is defect in globin chain production
--Most common: beta thalassemia --> mild micro-hypo anemia, highest incidence in N. Africans/Mediterraneans
--Minor: heterozygous, either alpha or beta chain, beta more common
--Major: homozygous beta thalassemia, aka COOLEY'S, Med origin, evident when adult Hgb production increases at age 2-3 mo, -->severe hemolytic anemia, frequent Howell-Jolly bodies, polychromatophilic (blue/red) RBC's, hypo-micro RBC's, anisocytosis & poikilocytosis, some target cells, death as child or adolescent
6. Understand the classification of anemias according to MCV and hemoglobin concentration
MICROHYPO = small cells with lowered hemoglobin
--IDA, iron deficiency, low iron content small cell size
--thalassemia
--lead poisoning
--some texts put anemia of chronic dz here
MACRONORMO = big cells normal iron content
--macrocytic anemia, normal iron content large cell size
--vit B12/folic deficiency
--SE of chemo
--myelodysplastic syndrome (BM abnormality resulting in decreased prod of RBC/WBC's OR precursor to development of ACUTE MYELOGENOUS LEUKEMIA, aka AML, as much as 30%)
NORMONORMO
--early iron deficiency
--chronic illness (anemia of chronic dz)
--oft renal dz
--acute blood loss
--aplastic anemia (chem exposure)
--acquired hemolytic anemia
7. Understand the 4 classes of porphyrias and be able to identify as hereditary or not
PORPHYRIA
1) erythropoietic (hereditary)
2) hepatic (acute intermittent in N Euros, abdom pain), variegate, hered corpoporphyria, porphyria cutanea tarda (PCT->blistering w/ sun exposure) (all hereditary & dominant??)
3) mixed (1 & 2) hepatoerythropoietic (recessive)
4) acquired (drug induced, lead poisoning)