CSMLS MLT Exam cheat sheet

Reference interval for fasting plasma glucose is roughly 3.9-5.5 mmol/L (70-99 mg/dL); diabetes diagnostic threshold on fasting plasma glucose is 7.0 mmol/L (126 mg/dL) confirmed on a second occasion.

Sodium is the major extracellular cation (~135-145 mmol/L); potassium is the major intracellular cation with plasma reference ~3.5-5.0 mmol/L; hemolysis falsely raises potassium.

Anion gap = Na - (Cl + HCO3), reference ~8-16 mmol/L; elevated gap suggests unmeasured anions such as ketones, lactate, uremic acids, or toxins.

Enzymatic creatinine (Jaffe or enzymatic method) plus urea reflects glomerular filtration; urea is affected by protein intake and hydration, creatinine less so.

Cardiac troponin I or T is the preferred biomarker for myocardial injury; rise and fall pattern plus clinical context defines acute myocardial infarction.

Alkaline phosphatase is elevated in cholestasis and bone disease; GGT elevation with ALP supports a hepatobiliary rather than bone source.

Hepatic aminotransferases (ALT, AST) mark hepatocellular injury; ALT is more liver-specific than AST, which also arises from muscle and red cells.

Plasma osmolality calculated = 2(Na) + glucose + urea (all in mmol/L); a measured-to-calculated gap >10 mmol/L suggests an unmeasured osmole such as ethanol or methanol.

Lipemia, icterus, and hemolysis interfere with many spectrophotometric assays; automated serum indices flag these interferences before result release.

Normal adult hemoglobin: men ~130-175 g/L, women ~120-155 g/L; MCV 80-100 fL, MCH 27-33 pg, MCHC 320-360 g/L.

Reticulocyte count corrected for anemia = reticulocyte % x (patient Hct / normal Hct); an elevated corrected count indicates a hyperproliferative marrow response.

Iron deficiency anemia is microcytic with low ferritin and high TIBC; anemia of chronic disease is normocytic with low TIBC and normal-to-high ferritin.

Megaloblastic anemia shows macrocytosis and hypersegmented neutrophils; B12 deficiency can also cause neurologic signs, folate deficiency typically does not.

Platelet reference interval ~150-400 x 10^9/L; pseudothrombocytopenia from EDTA-dependent platelet clumping is excluded by examining a citrate or smear sample.

D-dimer has high sensitivity but low specificity for venous thromboembolism; a negative result in a low-probability patient helps exclude the diagnosis.

PT/INR monitors warfarin (extrinsic pathway); aPTT monitors unfractionated heparin (intrinsic pathway); both are prolonged in disseminated intravascular coagulation.

Sickle cell screening uses a solubility or hemoglobin S detection method; confirmation and variant identification require hemoglobin electrophoresis or HPLC.

A left shift with toxic granulation and Dohle bodies suggests acute bacterial infection or severe inflammation rather than a benign reactive change.

Gram-positive cocci in clusters suggest Staphylococcus; in chains suggest Streptococcus; in pairs suggest Enterococcus or Streptococcus pneumoniae.

Catalase-positive, coagulase-positive gram-positive cocci identify Staphylococcus aureus; coagulase-negative staphylococci are typical skin flora but can be significant with indwelling devices.

Beta-hemolysis on blood agar with bacitracin sensitivity suggests Streptococcus pyogenes (group A); bacitracin resistance suggests group B streptococcus.

Oxidase-positive, non-fermenting gram-negative rods include Pseudomonas aeruginosa; oxidase-negative enteric rods are typical Enterobacterales.

MacConkey agar selects gram-negative bacteria and differentiates lactose fermenters (pink) from non-fermenters (colorless).

Minimum inhibitory concentration is the lowest antimicrobial concentration that inhibits visible growth; broth microdilution and gradient strips report MICs directly.

Blood cultures should be collected before antimicrobial therapy, typically two to three sets from separate sites; each set includes an aerobic and anaerobic bottle.

Clostridioides difficile testing is best on unformed stool; nucleic acid amplification detects toxin genes and does not distinguish colonization from active disease.

Mycobacterium species require acid-fast staining and prolonged culture; auramine-rhodamine fluorescence is a common screening stain.

ABO typing requires both forward (cell) and reverse (serum) grouping; discrepancies require resolution before transfusion.

Group O red cells carry no A or B antigen; group AB plasma lacks anti-A and anti-B and is the universal plasma donor.

Rh immune globulin prevents anti-D alloimmunization in D-negative mothers; the dose is guided by the fetomaternal hemorrhage volume.

The indirect antiglobulin test detects unexpected antibodies in serum; the direct antiglobulin test detects antibody or complement on red cells in vivo.

Antibody screen positive results require identification with a panel; clinically significant antibodies include those to Rh, Kell, Duffy, Kidd, and MNS systems.

Crossmatch incompatibility may reflect an antibody against donor antigens; the antibody identification and selection of antigen-negative units is required.

Red cells may be stored at 1-6 degrees Celsius for up to 42 days depending on the preservative solution; platelets are stored at 20-24 degrees with agitation.

Transfusion reaction workup includes repeat ABO testing, DAT, visual inspection of pre- and post-transfusion samples, and culture when bacterial contamination is suspected.

Febrile nonhemolytic reactions are the most common transfusion reaction; acute hemolytic reactions typically present with fever, chills, flank pain, and hemoglobinuria.

Formalin fixation at 10% neutral buffered formalin cross-links proteins; overfixation can mask antigens and impair immunohistochemistry.

Tissue processing dehydrates through graded alcohols, clears with xylene, and infiltrates with paraffin; incomplete clearing leaves cloudy blocks.

Hematoxylin stains nuclei blue-purple (basophilic); eosin stains cytoplasm and collagen pink (eosinophilic).

The periodic acid-Schiff stain highlights glycogen and mucin; diastase digestion distinguishes glycogen (removed) from mucin (retained).

Masson trichrome stains collagen blue-green and muscle red; useful for assessing fibrosis.

Prussian blue demonstrates hemosiderin iron; the Perls reaction turns iron deposits blue.

Frozen sections are used for intraoperative consultation; they preserve lipids and antigens but have less morphologic detail than paraffin sections.

Antigen retrieval (heat or enzyme) is often required before immunohistochemical staining of formalin-fixed paraffin-embedded tissue.

Decalcification of bone uses acid or chelating agents; strong acids can damage nucleic acids and some antigens.

IgM antibodies appear early in infection and are pentameric; IgG appears later, is monomeric, crosses the placenta, and dominates the secondary response.

The classic complement pathway is activated by antigen-antibody complexes; the alternative pathway is antibody-independent and activated by microbial surfaces.

Antinuclear antibody testing by immunofluorescence is a screening test for systemic lupus erythematosus; a positive result requires clinical correlation.

Anti-double-stranded DNA and anti-Smith antibodies are specific for systemic lupus erythematosus; anti-dsDNA titers may track disease activity.

Rheumatoid factor is an antibody against the Fc portion of IgG; it is sensitive but not specific for rheumatoid arthritis.

Anti-cyclic citrullinated peptide antibodies are more specific than rheumatoid factor for rheumatoid arthritis.

Enzyme immunoassay and chemiluminescence are common screening formats; confirmation of reactive results uses a different method such as immunoblot or nucleic acid testing.

A positive syphilis screening test requires a treponemal confirmatory test; reverse algorithms start with a treponemal assay and reflex to a nontreponemal test.

Allergy testing by specific IgE measures sensitization; a positive result does not by itself establish clinical allergy.

Standard precautions treat all blood and body fluids as potentially infectious; gloves, gown, and eye protection are used according to task risk.

Chemical hazard communication requires safety data sheets, labeling, and training; formaldehyde and xylene require ventilation and exposure monitoring.

Biological spills are managed by containment, absorbent application, disinfection with an appropriate agent, and proper disposal.

Westgard multirule QC uses 1-2s as a warning rule and 1-3s, 2-2s, R-4s, and 4-1s as rejection rules.

A shift in QC values indicates a systematic error such as a calibration or reagent problem; a trend suggests gradual deterioration of reagent or instrument.

Levey-Jennings charts plot QC results over time with mean and standard deviation limits; random error increases scatter, systematic error shifts the mean.

External quality assessment (proficiency testing) compares performance with peer laboratories and is required for accreditation.

Root cause analysis and corrective and preventive action follow an incident; documentation must show investigation and monitoring of effectiveness.

Delta checks flag results that differ unexpectedly from a patient's previous result and require review before release.

Order of draw for venipuncture: blood culture, sodium citrate (coagulation), serum tube with or without clot activator, heparin tube, EDTA tube, fluoride-oxalate tube.

Sodium citrate tubes must be filled to the marked volume; underfilling alters the blood-to-anticoagulant ratio and prolongs clotting times.

EDTA tubes are used for hematology and bind calcium; heparin tubes are used for chemistry and do not bind calcium.

Hemolysis from traumatic venipuncture falsely raises potassium, LDH, and AST and interferes with many assays.

Prolonged tourniquet application causes hemoconcentration and falsely raises protein, potassium, and cell counts.

Blood cultures should be drawn before antibiotics and incubated promptly; delayed incubation reduces recovery of fastidious organisms.

Urine for culture should be midstream, collected in a sterile container, and transported promptly or refrigerated.

Timed collections such as 24-hour urine require proper preservative and complete collection; incomplete collection invalidates results.

Specimen labeling must occur at the bedside with two patient identifiers; unlabeled or mislabeled specimens are rejected.

Coefficient of variation (CV) = (standard deviation / mean) x 100; it expresses precision as a percentage.

Standard deviation from a set of values = square root of the sum of squared deviations divided by (n - 1).

Mean = sum of values divided by number of values; the median is the middle value when values are ordered.

Dilution calculation: concentration of original = measured concentration x dilution factor; for a 1:10 dilution the factor is 10.

Serial dilution: each step multiplies the dilution factor; three consecutive 1:10 dilutions give a 1:1000 final dilution.

Beer-Lambert law states absorbance is proportional to concentration and path length; deviations occur at high absorbance or with stray light.

Spectrophotometers measure absorbance; nephelometers measure scattered light and are used for immunoglobulins and specific proteins.

Ion-selective electrodes measure electrolyte activity; indirect methods dilute the sample and can be affected by hyperproteinemia or hyperlipidemia.

Calibration establishes the relationship between signal and concentration; it differs from QC, which verifies ongoing performance.

Urine specific gravity by reagent strip reflects ionic concentration; the refractometer measures refractive index and is less affected by glucose or protein.

Urine pH reference is roughly 4.5-8.0; alkaline urine can result from urease-producing organisms or prolonged storage.

A positive urine leukocyte esterase suggests pyuria; a positive nitrite test suggests nitrate-reducing bacteria such as Enterobacterales.

Hematuria with dysmorphic red cells and red cell casts suggests glomerular bleeding rather than lower urinary tract bleeding.

Hyaline casts are nonspecific; red cell casts indicate glomerulonephritis and white cell casts suggest pyelonephritis.

Pleural fluid is classified as transudate or exudate using Light criteria; exudates typically have elevated protein or lactate dehydrogenase relative to serum.

Cerebrospinal fluid should be transported promptly and examined for cell count, glucose, protein, and Gram stain; bacterial meningitis shows neutrophilic pleocytosis and low glucose.

Synovial fluid with needle-shaped negatively birefringent crystals suggests gout; rhomboid positively birefringent crystals suggest pseudogout.

Urine reagent strip protein is most sensitive to albumin; Bence Jones proteins may be missed and require alternative testing.