MLS flashcards
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- Direct antiglobulin test
- DAT detects antibody or complement coating red cells in vivo; it is used to investigate hemolytic disease of the newborn, autoimmune hemolysis, and transfusion reactions.
- Universal red cell donor
- Group O donors lack A and B red cell antigens, so their red cells can be transfused to recipients of any ABO group; their plasma contains anti-A and anti-B.
- Indirect antiglobulin test
- The indirect antiglobulin test detects unexpected antibodies in patient serum after incubation with reagent red cells and antihuman globulin; it underlies the antibody screen and crossmatch.
- Platelet storage conditions
- Platelets are stored at 20-24 degrees Celsius with continuous gentle agitation for up to 5 days; refrigeration causes shape change and reduces post-transfusion viability.
- Anion gap formula
- Anion gap equals sodium minus the sum of chloride and bicarbonate; the reference range is 8-12 mEq/L, and an elevated gap suggests ketoacidosis, lactic acidosis, or toxin ingestion.
- Friedewald LDL calculation
- LDL cholesterol equals total cholesterol minus HDL minus triglycerides divided by 5; the calculation is invalid when triglycerides exceed 400 mg/dL and direct measurement is needed.
- Corrected calcium formula
- Corrected calcium equals measured calcium plus 0.8 times (4.0 minus albumin in g/dL); it adjusts for hypoalbuminemia because roughly half of serum calcium is protein bound.
- Osmolal gap
- The osmolal gap is measured osmolality minus calculated osmolality (2Na + glucose/18 + BUN/2.8); a gap above 10 suggests methanol, ethylene glycol, or isopropanol ingestion.
- MCV calculation
- MCV equals hematocrit divided by red cell count, multiplied by 10 and reported in femtoliters; it classifies anemia as microcytic, normocytic, or macrocytic.
- Mixing study interpretation
- A 1:1 mix of patient plasma and normal plasma that corrects a prolonged PT or aPTT indicates factor deficiency; failure to correct indicates a circulating inhibitor such as a lupus anticoagulant.
- DIC laboratory pattern
- Disseminated intravascular coagulation shows thrombocytopenia, prolonged PT and aPTT, low fibrinogen, and elevated D-dimer or fibrin degradation products with schistocytes on the smear.
- Corrected reticulocyte count
- Corrected reticulocyte count equals reticulocyte percent times (patient hematocrit divided by 45); a value below 2% suggests an inadequate marrow response to anemia.
- Coagulase test
- Coagulase converts fibrinogen to fibrin; Staphylococcus aureus is coagulase positive, which distinguishes it from coagulase-negative staphylococci such as Staphylococcus epidermidis.
- Optochin sensitivity
- Streptococcus pneumoniae is optochin sensitive and bile soluble, whereas viridans streptococci are optochin resistant and bile insoluble, allowing laboratory differentiation.
- MacConkey agar
- MacConkey agar selects for gram-negative bacilli and differentiates lactose fermenters, which form pink colonies, from nonfermenters, which remain colorless.
- MRSA detection
- Methicillin resistance in Staphylococcus aureus is mediated by mecA; it is detected by cefoxitin disk diffusion, oxacillin MIC testing, or polymerase chain reaction for mecA.
- Primary versus secondary response
- The primary immune response produces IgM first after a lag of days; re-exposure produces a faster, larger, IgG-predominant response with antibodies of higher affinity.
- Hepatitis B serology
- HBsAg indicates current infection, anti-HBs indicates immunity, IgM anti-HBc indicates acute infection, and HBeAg reflects high infectivity and active viral replication.
- HIV testing algorithm
- Fourth-generation screening assays detect HIV p24 antigen and antibody; reactive results are confirmed with an HIV-1/HIV-2 antibody differentiation immunoassay rather than Western blot.
- Positive predictive value
- Positive predictive value equals true positives divided by the sum of true positives and false positives; it increases as disease prevalence rises in the tested population.
- Red cell casts
- Red cell casts indicate glomerular bleeding, as occurs in glomerulonephritis; dysmorphic red cells and significant proteinuria further support a glomerular source of hematuria.
- Struvite crystals
- Struvite or triple phosphate crystals appear as coffin-lid shapes in alkaline urine and suggest infection with urease-producing bacteria such as Proteus species.
- Light's criteria
- Pleural fluid is classified as an exudate if the protein ratio exceeds 0.5, the LDH ratio exceeds 0.6, or fluid LDH exceeds two-thirds the upper normal serum value.
- Synovial crystal birefringence
- Monosodium urate crystals in gout are needle shaped and negatively birefringent; calcium pyrophosphate crystals in pseudogout are rhomboid and positively birefringent.
- Real-time PCR cycle threshold
- The cycle threshold is the cycle at which fluorescence first exceeds background; lower Ct values indicate a higher initial copy number of the target nucleic acid.
- Sanger sequencing
- Dideoxynucleotides terminate chain elongation during Sanger sequencing; fragments separated by capillary electrophoresis yield the sequence used to detect point mutations.
- Factor V Leiden
- A point mutation (R506Q) in the F5 gene causes activated protein C resistance and thrombophilia; testing uses polymerase chain reaction or a functional APC resistance assay.
- No-template control
- A no-template control contains all reagents except nucleic acid; amplification in this tube signals contamination and invalidates the entire polymerase chain reaction run.
- Westgard 1-3s rule
- A control value exceeding the mean by more than three standard deviations is a rejection rule that indicates random error, most often an imprecision problem.
- Coefficient of variation
- Coefficient of variation equals standard deviation divided by the mean, multiplied by 100; it expresses assay imprecision as a percentage and allows comparison between analytes.
- Test sensitivity formula
- Sensitivity equals true positives divided by the sum of true positives and false negatives; it is the proportion of patients with disease who are correctly identified.
- Critical value reporting
- A result in a life-threatening range must be reported promptly to the responsible caregiver, with documentation of read-back, time, and the name of the person notified.