CLT8 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Order of draw

Sequence for collecting blood tubes: culture, citrate, serum, heparin, EDTA, fluoride. Follow it to prevent additive cross-contamination that alters coagulation and chemistry results.

Short-draw citrate effect

Underfilled light blue tubes raise the citrate-to-plasma ratio, falsely prolonging PT and aPTT. Fill to the indicated volume or recollect before reporting coagulation results.

Hemolysis interference

Rupture of red cells releases potassium, LDH, and AST into plasma, falsely elevating them. Reject or note the specimen; do not report hemolyzed potassium as a true value.

Fluoride oxalate tube

Gray-top tube containing sodium fluoride and potassium oxalate. Fluoride blocks glycolysis, preserving glucose, while oxalate anticoagulates by binding calcium.

Levey-Jennings chart

Plot of control results over time against mean and standard deviation lines. It shows random scatter versus systematic shift and supports Westgard rule application.

1-3s rule

One control value exceeds the mean by three standard deviations. It is a rejection rule indicating random error; the run should not be reported.

2-2s rule

Two consecutive control values exceed the same two-standard-deviation limit. It signals systematic error such as a shift in calibration or reagent lot.

Coefficient of variation

CV equals standard deviation divided by mean, multiplied by 100. It expresses precision as a percentage and allows comparison between analytes of different concentrations.

Anion gap formula

Sodium minus the sum of chloride and bicarbonate, normally about 8 to 12 mmol/L. An elevated gap points to unmeasured anions such as ketones, lactate, or toxins.

Friedewald LDL

LDL equals total cholesterol minus HDL minus triglycerides divided by five. It is invalid when triglycerides exceed 400 mg/dL, requiring direct measurement instead.

Corrected calcium

Measured calcium plus 0.8 times the difference between 4.0 and the albumin concentration in g/dL. It adjusts calcium for albumin binding in hypoalbuminemia.

Hemoglobin A1c

Glycated hemoglobin reflecting average glucose over about 120 days. Hemoglobin variants, recent transfusion, and altered red cell survival make it unreliable.

MCV interpretation

Mean corpuscular volume below 80 fL indicates microcytosis from iron deficiency or thalassemia. Above 100 fL indicates macrocytosis from B12 or folate deficiency and alcohol.

Mixing study

Patient plasma mixed with normal plasma and retested. Correction of a prolonged aPTT indicates factor deficiency; failure to correct suggests an inhibitor such as lupus anticoagulant.

PT versus aPTT

PT evaluates the extrinsic and common pathway, including factor VII. aPTT evaluates the intrinsic and common pathway, including factors VIII, IX, XI, and XII.

EDTA pseudothrombocytopenia

Platelets clump in EDTA anticoagulant, causing a falsely low automated count. Recollect in a citrate tube and examine the smear to confirm the true count.

Catalase and coagulase

Catalase distinguishes staphylococci from streptococci. Coagulase distinguishes Staphylococcus aureus from coagulase-negative staphylococci and is a key identification step.

Beta hemolysis

Complete clearing of red cells around colonies on blood agar, typical of Streptococcus pyogenes and agalactiae. Alpha hemolysis is green partial lysis; gamma is none.

MRSA detection

Cefoxitin disk diffusion or oxacillin minimum inhibitory concentration detects methicillin resistance mediated by the mecA gene, guiding avoidance of beta-lactam therapy.

Blood culture collection

Collect before antibiotics, 20 to 30 mL per adult set, inoculating the aerobic bottle first. Incubate at 35 to 37 degrees Celsius and never refrigerate.

Primary immune response

Initial antigen exposure produces IgM first, followed by a smaller, slower IgG response. Subsequent exposure yields a faster, larger IgG-predominant secondary response.

Sandwich ELISA

Capture antibody binds antigen, which is detected by a labeled second antibody. This format measures antigen concentration and requires two epitopes on the analyte.

Hepatitis B serology

HBsAg indicates current infection, anti-HBs indicates immunity, anti-HBc IgM indicates recent infection, and HBeAg indicates high infectivity. Interpret markers together.

Rheumatoid factor

Autoantibody directed against the Fc portion of IgG, found in rheumatoid arthritis and other conditions. Anti-CCP is more specific for rheumatoid arthritis.

RBC cast significance

Red cell casts in urine indicate glomerular bleeding from glomerulonephritis. Their presence localizes hematuria to the kidney rather than the lower urinary tract.

Light's criteria

Pleural fluid is an exudate if protein ratio exceeds 0.5, LDH ratio exceeds 0.6, or fluid LDH exceeds two-thirds the serum upper limit.

Urine nitrite test

Dipstick nitrite reflects nitrate reduction by Enterobacterales such as Escherichia coli. A positive result suggests significant bacteriuria, though some organisms do not reduce nitrate.

CSF glucose pattern

Bacterial meningitis lowers cerebrospinal fluid glucose and raises protein with neutrophilic pleocytosis. Viral meningitis usually shows normal glucose and lymphocytic pleocytosis.

Standard precautions

Treat all blood and body fluids as potentially infectious regardless of diagnosis. Apply gloves, gown, and eye protection based on anticipated exposure risk.

Centrifuge aerosol safety

Balance tubes and keep the lid closed during operation. After a break, wait 30 minutes before opening to allow aerosols to settle, then disinfect.

Beer-Lambert law

Absorbance equals molar absorptivity times path length times concentration. The linear relationship underlies spectrophotometric measurement and defines the analytical range.

Ion-selective electrode

Sensor measuring ion activity through a selective membrane. Indirect electrodes dilute the sample, so severe hyperlipidemia or hyperproteinemia can produce pseudohyponatremia.