Chemistry Flashcards
1
Q
Anion gap calculation
A
Na - Cl - HCO3
Should not exceed 12 normally
2
Q
Osmotic gap calculation
A
2Na + BUN/3 + Glucose/20
Should not exceed 10 normally
3
Q
Ketones in DKA
A
About 80% are beta-hydroxybutyrate, which is not detected by nitroprusside technique. Converted to acetoacetate/acetone which are detected (may have transient increase with treatment)
4
Q
Causes of anion-gap metabolic acidosis
A
Methanol Uremia Diabetic ketoacidosis Propylene glycol Isoniazid Lactate Ethanol Salicylates
5
Q
Causes of non-anion-gap metabolic acidosis
A
Bicarbonate losses (diarrhea, renal tubular acidosis)
6
Q
Water distribution
A
TBW is 60% water
2/3 of water is intracellular, 1/3 is extracellular
1/4 of extracellular water is intravascular (1/12 overall)
7
Q
Pseudohyponatremia
A
Spurious hyponatremia seen on indirect ISE methods where an assumed 93% water content is incorrect in the settings of patient hyperlipidemia or paraproteinemia.
8
Q
FENa
A
(Urine sodium * Plasma creatinine) / (Urine creatinine * plasma sodium)
If low (1%), reabsorption is functional.
9
Q
Causes of hypernatremia
A
Almost always dehydration or diabetes insipidus
10
Q
Causes of hyponatremia
A
Overhydration, SIADH
Wasting states (nephrotic syndrome, cirrhosis)
11
Q
Pseudohyperkalemia
A
Can be caused by hemolysis, collection into EDTA tube, clenching during phlebotomy or small needles.
12
Q
Causes of ture hyperkalemia
A
Hypoaldosteronism
Renal tubular acidosis
Renal failure
13
Q
CEA
A
Nonspecific family of surface glycoproteins expressed in many cancers (GI). Can be used for monitoring, not screening or diagnosis.
May transiently increase during chemotherapy. Higher in smokers.
14
Q
AFP
A
First expressed in yolk sac, then fetal liver (12wk).
Expressed in many tumors, but L3 variant is somewhat specific for HCC.
Can also be elevated in regenerative states, but very high levels suggest tumor.
15
Q
PSA
A
Prostatic specific antigen. Binds alpha-2-macroglobulin and alpha-1-antichymotrypsin
Levels of 4-10 are gray; look at free or pro-PSA levels (low % suggest cancer)
16
Q
CA15-3
CA19-9
CA125
A
CA15-3: Breast (MUC1, also CA27.29)
CA19-9: Lewis A, pancreatic cancer. Can be elevated in cholestasis.
CA125: Ovarian epithelial tumors (except mucinous)
17
Q
Whipple triad
A
Glucose <45mg/dL, symptoms of hypoglycemia, reversal with glucose administration
18
Q
DM diagnostic criteria
A
- Symptoms
2. Either fasting glucose > 126, random >200, 75g OGTT >200, or A1C > 6.5%,
19
Q
Detection of diabetes in hemoglobinopathies
A
Cannot rely on A1C due to shortened RBC lifespan. Look at FRUCTOSAMINE
20
Q
Microalbuminuria
A
Predicts diabetic nephropathy. Precedes decline in GFR.
Start checking annually after T2DM diagnosis, or +5yrs for T1DM.
21
Q
Creatinine clearance
A
Urine volume * urine creatinine [] / plasma creatinine
22
Q
MDRD formula
A
Calculates eGFR from Creatinine while considering age, gender, and ethnicity
23
Q
T3RU test
A
Measures TBG by incubating patient serum and radiolabeled T3 with a resin.
24
Q
Circulating thyroglobulin
A
Can be used as a marker of residual disease in thyroid cancer (PTC, FTC)
So too can anti-thyroglobulin antibodies, which are sometimes seen.
25
What causes increases or decreases in TBG?
Increases: Estrogen (pregnancy)
Decreases: Cirrhosis, nephrotic syndrome...
Note that TBG does not strongly affect free T3/T4 levels.
26
Thyroid hormone potencies
T3 > T4 > rT3 (inactivated)
27
Diurnal pituitary hormones
CRH/ACTH highest upon waking
| GH/GHRH highest upon sleeping
28
Diagnosis of hypercortisolism
Screen with urine free cortisol (24hr) or 1mg overnight suppression
Confirm with LOW-DOSE dexamethasone suppression test
Identify secondary hypercortisolism with ACTH level, HIGH-DOSE dexamethasone suppression
29
Diagnosis of adrenal insufficiency
Urine free cortisol
Cosyntropin test
30
Metyrapone
Blocker of 11-hydroxylase, prevents cortisol production
31
Aldosterone testing
Aldosterone:renin ratio >10 suggests hyperaldosteronism
Lateralize with petrosal sinus sampling
32
Plasma and urine catecholamine metabolites...
Pheochromocytoma: Check urinary fractionated catecholamines or plasma metanephrines
Neuroblastoma: Check urine HMA/VMA levels
Note: 5-HIAA is derived from serotonin, levels elevated in carcinoid syndrome
33
Prolactin signaling
Inhibited by dopamine from hypothalamus. May be the only normal hormone in panhypopituitarism.
Can be promoted by HYPOTHYROIDISM.
High-molecular weight forms may be specific for prolactinoma.
34
Bilirubin lab analysis
Direct bilirubin: Diazo method, does not use any accelerants (only detects conjugated)
Total bilirubin: Diazo method, uses caffeine or methanol to detect all.
35
Gilbert's disease
UGT1A1 mutation resulting in mildly reduced bilirubin conjugation. Flares with illness, benign.
Reduced metabolism of IRINOTECAN
36
Dubin-Johnson
Mutation of organic anion transporter. Results in direct hyperbilirubinemia and pigmentation of organs
37
Liver enzymes
AST: Nonspecific, also see in skeletal and cardiac muscle (elevated in exercise)
ALT: More specific for liver
GGT: Cholestatic marker, fairly specific
LDH: Non-specific, fast clearing
38
Liver autoantibodies
```
AMA - PBC, especially PDC-M3 variant
ASMA - Type 1 AIH
Anti-LKM - Type 2 AIH
Anti-soluble liver antigen - Type 3 AIH
pANCA - PSC
```
39
Wilson's disease
ATP7B transporter defect with resultant tissue accumulation of copper.
When not active/fulminant, low ceruloplasmin & copper. Otherwise note hemolysis
40
Hereditary hemochromatosis
XXXXXX
41
DeRitis Ratio
AST:ALT
Normally ALT > AST, but in alcohol, Wilson, cirrhosis, the ratio is reversed
42
Lactate dehydrogenase fractions
Normally LD2 > LD1 (both very common).
LD1 elevation / flipped ratio can be seen in acute infarctions or hemolysis.
43
Alkaline phosphatase
Many isoenzymes, can be distinguished by electrophoresis or heat inactivation
"Bone burns, liver lingers".
Regan isozyme - Placenta, tumors
44
Biliprotein
Bilirubin + albumin; accumulates in cholestatic states and takes days to clear.
45
Amylase
Elevated in pancreatitis, sialadenitis (lipase normal), macroamylasemia (spurious complex)
Less specific than lipase.
Needs calcium as a chelator, do not draw in blue/lavender tops.
46
D-xylose test
Measures gut absorptive capacity (not pancreatic exocrine function)
47
Fecal elastase
Superior to fat analysis or fecal chymotrypsin to assess pancreatic exocrine function
Must be performed on well-formed stools.
48
Troponins
Complex consists of cardiac troponins C (calcium), I, T (tropomyosin).
C: Same in cardiac and skeletal
I: Specific.
T: Specific.
49
CK-MB, myoglobin
CK-MB: Outdated MI marker.
Myoglobin: Totally nonspecific, but fast to rise and fast to fall.
50
NT-proBNP
Superior to biologically active BNP or ANP. Reflects systolic (not diastolic dysfunction)
51
MI diagnosis
Troponin >99th percentile
| One of: Symptoms, EKG abnormality, or wall motion abnormality
52
ACE
Can be elevated in sarcoidosis
53
```
Macro CK
Mitochondrial CK (macro CK type 2)
```
Macro CK: Immunoglobulin complex seen in some elderly women
| Mitochondrial CK: SUggestive of some advanced malignancies.
54
hsCRP
Predictor for development of acute coronary syndrome
JUPITER study
55
Cryoglobulinemias
Type I: Monoclonal only; associated with lymphoproliferative disorders
Type II: Monoclonal and polyclonal component; associated with HCV
Type III: Polyclonal only; associated with autoimmune disorders
56
Calcium assay
Colorimetric assay
| Ionized assay
57
Urinary CAMP
Increased in hyperparathyroidism
58
Forms of parathyroid hormone
Intact - Active, short-lived
N-terminal - Active, short-lived
C-terminal - Inactive, long-lived
59
Co-oximetry
Uses 4 wavelengths of light
Distinguishes oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin, methemoglobin
Does not detect sulfhemoglobin
60
FSH/LH secretion
Responds to continuous GNRH secretion (continuous inhibits)
Surge in ovulation. Estrogen predominates in follicular phase, progesterone in luteal phase.
61
Estrogens
E1: Estrone, mostly post-menopausal
E2: Estradiol, most potent
E3: Estriol, placental/pregnancy
62
AMH
Produced by granulosa cells, marker of ovarian reserve. Elevated in PCOS due to failure of selection of a dominant follicle.
63
hCG in pregnancy
Doubles every two days (if normal intrauterine)
Peaks at end of third trimester, holds through pregnancy
Takes 2 weeks postpartum to clear
*Hyperglycosylated form predominates in early pregnancy
64
First trimester screen
hCG, PAPP-A, nuchal thickness.
For down syndrome.
65
Quad screen
hCG / Inhibin / Estriol / AFP
t21: + / + / - / -
t18: - / - / - / -
NT defect: AFP elevated
66
MSAFP
If >2.5 MoM, high risk of birth defects.
LOW in t21!
67
Markers of fetal lung maturity
LS ratio of 2.5:1 (less lecithin suggests immaturity)
PG concentration
Lamellar body count (more = mature)
68
Pregnancy marker changes
eGFR increases >> lower creatinine, BUN. Proteinuria, glucosuria
Increased fibrinogen, (relatively) decreased albumin
Dilutional anemia despite increase in red cell mass
69
Lipoprotein compositions
Chylomicrons: Triglycerides.
VLDL: Triglycerides.
LDL: Cholesterol, Apo-B100
HDL: Cholesterol, Apo-A
70
Friedewald calculations
VLDL is estimated as TG/5.
LDLc = TC - HDL - VLDL
71
Abetalipoproteinemia
Low triglycerides and low cholesterol.
ACANTHOCYTES on peripheral smear.
Developmental delay, fat malabsorption...
72
Frederickson phenotypes of hyperlipidemias
I - Hyperchylomicronemia (TGs, LPL or ApoC2 def)
II - A (LDL), B (VLDL, LDL)
III - ApoE2/E2
IV - VLDL, associated with insulin receptor mutations and lipodystrophy
V - Chylomicrons, VLDL
73
LPL effect
LCAT effect
CETP effect
LPL: Hydrolyzes VLDL to form IDL/LDL
LCAT: Transfers lipids to HDL
CETP: Exchanges lipids between HDL and lower density particles
74
Tangier disease
Autosomal recessive disorder of absent HDL.
75
ATP III recommended targets
TC: <200
LDL: Optimal <100, near optimal 100-129, borderline 130-159
HDL: <40 low, >60 high
76
GDM testing
2-step: 50g OGTT (target X), then 100g OGTT (target Y
| 1-step: 75g OGTT (target 180, 153 at 1, 2 hours)
77
Fecal occult blood testing
Guaiac based testing prone to false-positives (NSAIDs, red meat, peroxidase (horseradish)) and false-negatives (Vitamin C consumption)
Immunochemical based methods are less affected.
78
Euthyroid sick syndrome
Low T3, T4
Elevated rT3?
Nomral TSH.
Just peripheral inactivation of thyroid hormone. Thyroid function is normal.
79
T3RU
Measures available binding sites on thyroid binding globulins.
Mix patient sample with radioactive iodine (binds available sites), then resin-adsorb and see how much radioactive iodine remains.
High residual levels means few binding sites (hyperthyroidism). Low residual levels in hypothyroidism.
80
High-dose dexamethasone suppression
Distinguishes pituitary corticotroph adenoma (Cushing disease) which should suppress from ectopic ACTH production (does not suppress).
81
Granulosa cells - Hormonal profile
Secretes both steroid hormones (testosterone, estrogen, etc) and peptide hormones (AMH, inhibin).
May have elevated AFP serum levels (not CA-125!)
82
Confirmatory test for Conn syndrome
Isotonic large volume saline infusion >> failure to suppress aldosterone
83
Gestational thyrotoxicosis
Elevated bHCG levels cross-react on TSH receptor. Should co-occur with hyperemesis gravidarum
84
CTX, NTX
Bone resorption markers.
High variability according to diet, circadian rhythm
85
Pseudohypoparathyroidism
Peripheral resistance to PTH.
Associated with GNAS (McCune-Albright)
86
Apt test
Distinguishes fetal hemoglobin from adult; fetal hemolysate resists denaturing in 1% NaOH
87
IBD serologies
Crohn's: Anti-saccharomyces cerevisiae (ASCA)
| UC: pANCA (as in PSC)
88
Schilling test
Test for failure of B12 absorption. Give oral load of radiolabeled B12, inject non-radiolabeled. Measure urine.
Done in stages with progressive replacement of IF, pancreatic enzymes
89
Celiac serology
TTG is best test for diagnosis
| Anti-endomysial IgA (EMA) may disappear after diet improvements
90
Carbohydrate-deficient transferrin
Old, shitty test for alcohol abuse
91
Non-HBV hepatitis serologies
Anti-HAV: Total for screen, IgM for confirm
Anti-HCV: IgG only (no IgM)
92
Hyperviscosity
Falsely depresses most assays/analytes
93
Timing of cardiac biomarkers
Myoglobin rises and falls first
CK-MB and troponins all have similar timing (detectable in 4-6 hrs, peak in 10-24hrs)
94
Skin sweat chloride test
Gold standard for CF diagnosis.
Performed using coulometric titration
95
Grey-tops
Contains sodium fluoride to halt in-tube glycolysis. For glucose measurements.
96
Jaffe reaction
Detects creatinine by forming a chromogen (alkaline picrate). Affected by interfering substances ~520nm.
97
Convert urea to BUN
Divide by molar ratio of nitrogen to urea molar weight-- 60/28, or divide by 2.14.
98
Pseudohypokalemia
Can be seen in some leukemic specimens; cells (especially blasts) may take up extracellular potassium
99
Fatty- acid oxidation defects
Usually present with hypoglycemia and low ketones (cannot mobilize fat stores)
100
Most common urea cycle defects
| Most common organic acidemias
Urea cycle: Ornithine transcarbamylase deficiency (X-linked recessive)
Organic acidemias: Methylmalonic, priopionic acidemias
101
Transient hyperkalemias
Exercise
| Shift to upright positioning (third-spacing of free water)
102
Familial hyperkalemia
| Familial hypocalciuric hypocalcemia
FH: Autosomal dominant defect of RBC membrane >> leakage in storage
FHH: Benign condition of decreased urine calcium excretion >> as name suggests
103
RTAs
Type 1: Distal. Poor hydrogen excretion means urine cannot acidify. Alkaline urine. Hyperchloremic.
Type 2: Proximal. Failure to reabsorb bicarb, but distal compensation can acidify urine. Hyperchloremic.
Type 4: Failure of aldosterone. Hyperkalemic! Acidic urine.
104
Pseudohypoparathyroidism
Renal disease
Low calcium, high potassium
High parathyroid hormone
105
NAD+, NADH absorption
NAD: 260nm
NADH: 340nm
Can see interference with lactic samples or high LDH samples
106
Rickets
Low calcium, LOW PHOSPHATE, high PTH
107
Procalcitonin
Inflammatory marker that is suggestive of bacterial infection
108
Testosterone testing
Immunoassays (insensitive, only use in men or when high levels are expected)
Mass spec (for women, children, tumors?)
109
Triglyceride testing
Relies on hydrolysis of glycerol; false elevations may be seen in hyperglycerolemic states (glycerol kinase deficinecy)
