2. Interference occurs when a substance or process
falsely alters an assay result.
These altered results may lead to repeat tests,
incorrect diagnoses, and treatments with potentially
unfavorable outcomes for the patient.
2
4. Endogenous interference originates from
substances found naturally in the patient sample.
Hemolysis
Bilirubin
Lipids
Paraproteins
Excessive analyte concentration
4
5. Exogenous interference results from
substances not naturally found in the patient’s
specimen.
Drugs
Poisons
Herbal products
IV fluids
Substances used as therapy (Antibodies)
Collection tube components
(Anticoagulant)
Test sample additives (Preservatives)
5
6. Hemolysis is the release of hemoglobin and other
intracellular components of erythrocytes and
other blood cells to the surrounding plasma
following damage of the cell membrane.
Hemolysis occurs in about 3% of all specimens
received in the laboratory and accounts for 40%
to 70% of all unsuitable specimens.
Hemolysis may occur either in vivo or in vitro.
6
7. In vivo hemolysis can originate from:
7
Inherited hemolytic anemia
Defect in hemoglobin production
(Thalassemia, Sikckle cell disease)
Defect in RBC membrane
(Spherocytosis, Elliptocytosis, PNH)
Defect RBC metabolism
(G6PD, Pyruvate kinase deficiency)
9. Usually less than 2% of all the specimens with
hemolysis may be due to in vivo hemolysis.
In vivo hemolysis does not depend on the
technique of the healthcare provider and it is thus
virtually unavoidable and cannot be resolved.
9
10. In vitro hemolysis can occur beginning at the
patient’s bedside and continue through sample
handling, processing and storage.
Leading causes of in vitro hemolysis:
Patient dependent
Operator dependent
Device dependent
Handling of the specimen
Transport of the specimen
Sample processing
Sample storage
10
11. 11
Differentiating between in vivo and in vitro
hemolysis is vitally important to patient
management
In vitro hemolysisIn vivo hemolysis
Haptoglobin↓ Haptoglobin
↑ AST
↑ Unconjugated
Bilirubin
↑ K↑Reticulocytes
↑ LDHLDH↑
13. Additive: Several constituents are normally present in large
amounts within the red blood cells. When the red blood cells
burst these substances will be released and their values will
become falsely elevated (LDH, K, AST).
13
E/P RatioPlasmaErythrocytesSubstance
16036058000LDH, U/L
22.84.4100.0Potassium, mmol/L
2025500AST, U/L
73.022.0APs, U/L
530150ALT, U/L
14. Dilutional: release of intracellular fluid into the
surrounding extracellular area, the extracellular fluid
becomes more dilute and analytes will appear falsely
low (Na, Cl, Ca).
14
E/P RatioPlasmaErythrocytesSubstance
0.110.01.0Calcium, mg/dL
0.11140.016.0Sodium, mmol/L
0.5104.052.0Chloride, mmol/L
15. Chemical: by hemolysis there is several substances in
the solution that may cross-reacting with the analyte.
Adenylate kinase (CK and CKMB)
Pseudoperoxidase activity of hemoglobin (Bilirubin)
Heme group (Iron)
15
16. Spectral: Hemoglobin shows strong absorbance
at 415 nm and have two peaks at 540 and 570
nm. Therefore it may greatly interfere with
measurement at these wavelengths.
16
17. 17
Hemolyzed
Sample
Quantification of Hemolysis
Clinically or analytically
Significant
Clinically or analytically
Insignificant
Perform analyses and report
result without warnings
Analyses unaffected
by hemolysis
Do not perform analyses and
ask for an additional Sample
Analyses Affected
by Hemolysis
perform analyses and report
result with warnings
If the recollected specimen is also hemolyzed,
perform analyses and report result with warnings
18. 18
Test to be
suppressed
Free
Hemoglobin
Degree of
Hemolysis
• LDH
• Potassium
• AST
25-50 mg/dLSlightly
• CK & CKMB
• ALP
• ALT
50-200 mg/dLModerate
Virtually all test200 mg/dL≤Sever
The amount of hemolysis needed to affect a test is
dependent on the test being performed.
19. 19
Lipemia is the presence of a fine emulsion of
fatty substance in the blood.
It is characterized by turbidity of samples which
may range from slightly opaque through
transparent, turbid to milky appearance.
22. The overall frequency of lipemic samples ranges
from 0.5-2.5 %, depending on the type of hospital
and proportion of inpatient and outpatient samples.
22
31. 31
Extraction
Extraction of lipoproteins into hydrophobic
phase
Polyethylene glycol
Cyclodextrin
Lipoclear
32. 32
Sample dilution
Sample can be diluted only enough to remove the
turbidity interference (2 or 3 fold).
33. 33
Icterus is the yellowish discoloration of skin
and mucous membrane and body fluids,
resulting from increased level of bilirubin in
the plasma (Hyperbilirubinemia).
Patient dependent (Fragile veins, difficult venous access)
Operator dependent (Skill of the operator, Location of needlestick, Traumatic blood draw, Missing the vein, Drawing from a hematoma, capillary collection, antiseptic used, prolonged tourniquet, Tube underfilling)
Device dependent (Small gauge needles, Butterfly devices, Use of the lancet)
Handling of the specimen (No mixing or insufficient mixing, excessive mixing, syringe transfer)
Transport of the specimen
Sample processing
Sample storage
The upper reference limit for free hemoglobin is 5 mg/dL for serum.
Visually, hemolysis is defined as free hemoglobin concentration > 50 mg/dL.
Because lipids are water-insoluble molecules, they cannot be transported in aqueous solutions, such as plasma. For that reason, lipids are transported in plasma as macromolecular complexes known as lipoproteins Lipoproteins are spherical structures that consist of a hydrophobic core containing lipids (i.e. triglycerides and/or cholesterol esters), and an amphophilic (i.e. both hydrophobic and hydrophilic) outer layer of phospholipids, free cholesterol, and proteins that forms a protective envelope surrounding the lipid core
Plasma lipoproteins differ in their physical and chemical characteristics such as size, density, and composition. Canine lipoproteins can be divided based on their hydrated density into four major classes: (1) chylomicrons, (2) very low-density lipoproteins (VLDL), (3) low-density lipoproteins (LDL), and (4) high-density lipoproteins (HDL)
not all classes contribute equally to the turbidity. The largest particles, chylomicrons, with sample size of 70-1000 nm, have the greatest potential in causing turbidity of the sample. Accumulation of small particles, high density lipoproteins (HDL), low density lipoproteins (LDL) and small very low density lipoproteins (VLDL) doesn’t result with lipemic samples
Bilirubin may interfere by acting as a reducing substance as it is easily
oxidized to biliverdin and bilipurpurin with a reduction in absorbance.
Assays that utilize oxidase/peroxidase based reactions to produce hydrogen
peroxide, may produce lower results because bilirubin reacts with the
H2o2 formed in the test system. The reduction in H2o2 is relative to the
concentration of bilirubin present. This is true for enzymatic procedures
that are used for the measurement of glucose, cholesterol, triglycerides
and uric acid.
In albumin assays that employ dye binding, bilirubin can competitively
bind to the dye and produce lower albumin results.
Bilirithin. Elevated concentrations of bilirubin are another
source of endogenous interference. Part of the
interference arises from the spectral properties of bilirubin,
another part from bilirubin’s ability to react
chemically with reagents. Bilirubin reacts with peroxidase-
catalyzed reactions, as are used in the detection
systems for glucose, cholesterol, and uric acid (32). Bilirubin
causes a negative interference with the Jaff#{233}
method for creatinine, as measured with the Paramax
(Baxter), the Dimension (DuPont), or the Chem-1
(Bayer-Technicon) analyzers (37, 38). Also, bilirubin
causes a negative interference with the enzymatic
method for creatinine that is based on creatinine, creatinase,
and sarcosine oxidase and detects H2O2 with peroxidase
(39). Bilirubin interferes with determinations of
uric acid, cholesterol, and triglycerides that use peroxidase-
coupled reactions (40). Part of the interference is
chemical, thought to be caused by the destruction by
bilirubin of a reaction intermediate, which is partially
corrected by adding ferrocyanide to the reagents (40).