Labs / Assays Flashcards
(9 cards)
What is a cause of falsely low or high TFTs?
Interference often caused by autoantibodies– ex T4 autoantibody. Polyethylene glycol in serum precipitates immunoglobulins. Interfere with automated assays.
What causes falsely high insulin levels?
Insulin, cpeptide, proinsulin elevated. Significant insulin antibodies– can interfere with all of these assays. Can cause insulin resistance OR hypoglycemia (when released at the same time). Can measure free and total insulin– majority will be bound to antibodies. They are low affinity and high capacity.
What causes TSH elevation with elevated or normal hormone levels?
Human anti-mouse antibodies (HAMA) frequently cause false high TSH. Can neutralize with mouse serum. Up to 5% of population have this antibody, but usually milder– can interfere with antibody based sandwich assay.
What is HAMA and what does it do to lab tests?
HAMA is human anti mouse antibody, binds with interference and gives false high value for any sandwich based antibody test.
Falsely elevated HCG levels when not pregnant- cause and what do you do?
Follow HCG levels and watch for rise (for choriocarcinoma). HCG measurement can be elevated due to HAMA. Cross check with urine– will be normal. OR dilute and watch for linearity– if not linear, suspect interference.
What patients have a higher development of HAMA?
Patients on immunoglobulin therapy.
Hook effect?
When ab capacity of test is overwhelmed by the antigen and get more mildly elevated result. For example, prolactin and TG (>1000 ng/ml), only about 1-2% of samples. Run undiluted and 1:10 dilution.
What supplement can interfere with some immunoassays?
Biotin supplements - due to strepavidin-biotin interaction, biotin will bind the other antibody and take it out of assay (cause false low PTH for example).
What can go wrong with one step immunoradiometric assay?
HAMA (false positive), hook effect (Tg, HCG, PRL). Either select two step ICMA or dilute.
