Lecture Notes: Endocrine tests, serology


Nurs 466: Serum Lab Values

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Objectives: 

  1. Describe the use of free T4, total T4, T3 and TSH in determining if patient has primary or secondary hypothyroidism.
  2. Which tests are best to monitor treatment of hypothyroidism and hyperthyroidism?
  3. Which test will indicate active hepatitis B infection, previous hepatitis B infection?
  4. If a woman wants to become pregnant, which titer will tell her she has immunity against rubella?
  5. Which cancer markers tell you where the cancer is located?
  6. How do toxicology tests differ from therapeutic drug monitoring tests?
  7. What carbon dioxide level is lethal?
  8. What level of ethanol indicates intoxication?

 

Thyroid Hormones

Iodine is concentrated in the thyroid gland. Iodine is essential to synthesis of thyroid hormone, which stimulates metabolism and is needed for growth and development. Ingested iodides are absorbed from GI tract and removed from blood by thyroid gland. In the gland one iodine atom is incorporated into an amino acid to form monoiodotyrosine. Another iodide is added to form di-iodotyrosine. Triiodotyrosine (T3) is formed when a mono and di combine. Thyroxine (T4) is formed when two di’s combine. 90-95% of thyroid hormone in serum is T4, the rest is T3. 99% of circulating hormone is reversibly bound to protein.

Hypothalamus forms thyrotropin-releasing hormone
Pituitary forms TSH

When blood levels fall, thyrotropin releasing hormone is scereted by hypothalamus. TRH stimulates anterior pituitary to secrete TSH. Increased T3 and T4 have negative feedback which inhibits TSH.

Free Thyroxine (T4)

Not bound to protein
Normal 1-2.3 ng/dl
Taking levothyroxine may be up to 5 ng/dl
Heparin causes false highs

T4-RIA

Measures level of total circulating thyroid hormone
Same as T4, but done as radioimmunoassay

Total T4

Direct measurement of total thyroxine in blood
5% bound to TBG, ablumin and pre-albumin

T3-RIA

Test of choice if think there is T3 thyrotoxicosis, uses radioimmunoassay
Thyroglobulin

Used to follow patients with thyroid cancer
Contains precursors of thyroxine and triiodothyronine and the hormones themselves

T3 Uptake Ratio

Indirect measure of unsaturated thyroxin binding globulin in blood
Inversely related to UTBG
Decreased in pregnancy, estrogen therapy, oral contraceptives, methodone and heparin
Increased with dicumoral, heparin, androgens, anabolic steroids, phenytoin & salicylates.

Thyroid stimulating hormone

Produced in anterior pituitary
Stimulates thyroid to release stored thyroid hormones
Used to differentiate primary and secondary hypothyroidism
If hypothyroid and TSH is normal, consider hypopituitarism

Thyroxine binding globulin

Most important determinant of Free T4
Good approximation of thyroid binding function of the blood
Increased in pregnancy and with estrogen therapy
Decreased with anabolic steroid use, chronic liver disease & nephrosis

Radioactive iodine uptake

Tests thyroid ability to concentrate and retain iodine
Used to evaluate hypothyroidism, hyperthyroidism, thyroiditis, goiter, pituitary failure and to monitor treatment
More useful in hyperthyroidism
Increased uptake suggests hyperthyroidism
Decreased uptake may be caused by hypothyroidism

*Study the table on page 413 to differentiate which tests are best for hypo- and hyperthyroidism

Interpreting Thyroid Tests This site provides a diagram to help you understand what an elevation or decrease in the tests indicates.

Serology Tests

Hepatitis tests

Serological Marker Time after infection
HAV-AB/IgM
HAV-AB/IgG		 4-6 weeks
8-12 weeks
HAVsAB (surface antigen)
HBcAB (core antibody)
HBeAG (B-e antigen)
HBeAB (B-e antibody)
HBsAB (surface antibody)		 4-12 weeks
6-14 weeks
4-12 weeks
8-16 weeks
2-10 months
HCV antibody 2 weeks to 6 months
HDV antibody
HEV
HGV

 

Hepatitis A antibodies appear from 4-6 weeks after exposure and remain in the blood indefinitely. The initial antibodies are of immunoglobulin M class. Later replaced by immunoglobulin G class and indicate immunity to hepatitis A. Patient usually recovers in 4-6 months.

Hepatitis B antigen and core antigen are detectable throughout the acute stages of the illness Hepatitis B surface antigens can be found in the blood 4-12 weeks after exposure. Patients are infectious as long as hep B surface antigens are present Incubation period can last from 6 weeks to 6 months.

Hepatitis C – diagnosis made when S/S hepatitis present, liver function tests are abnormal and hepatitis A and B tests are negative. Incubation period of 2 weeks to 6 months. 

Hepatitis D -  Anti-HDV is available for assay. Occurs only in presence of Hepatitis B

Hepatitis E – antibody assay not available at this time

Hepatitis G – chronic hepatitis, transmitted percutaneously, associated with disease lasting more than 10 years. Does not interfere with antiviral therapy for hepatitis A or B.

Strep Infections

· Anti-streptolysin-O (group A strep)

Antibodies appear 7-10 days after infection
Peak 2-4 weeks
Remain high for months

· Antideoxyribonuclease-B

Measures antibody against strep enzyme

· Streptozyme – measures 5 different strep enzymes

Rubella

German or 3 day measles
Important only if pregnant
Titer of 1:32 indicates immunity

Tests to assess cancer

Tumor markers

Lung                Breast   Prostate   Testicular Gastrointestinal
CK-BB CK-BB PSA   Calcitonin CEA
CEA   CA 15-3 PAP    HCG CA 50
CA 15-3 CA 549 CA 549 AFP CA 19-5
CA 549 CA 19-9   CA-72-4
 

Hepatocellular

  

Colorectal 

  

Pancreatic

  

Ovarian   

  

Bone  

  

Thyroid
CA 19-9 CEA CEA  CK-BB Alk Phos Calcitonin
AFP    CA 15-3 CA 50 CA 125
Alk Phos CA 19-9 CA 19-9   CA 15-3
CA 50  CA 15-3   CA 549
CA 72-4

CA 15-3 & CA 27.29

Serum marker for staging breast cancer & monitoring its treatment of advanced disease
Localized breast cancer 50%
Metastatic breast cancer 80% Ca 15-3 and 65% Ca 27.29
Not useful as screening tool

Also elevated in

  • Non-breast cancers (lung, pancreas, ovary, prostate)
  • Benign breast disease
  • Cirrhosis
  • Hepatitis

Not used for post-treatment surveillance
Many false positives

CA 19-9

Carbohydrate antigen 19-9

Tumor marker for pancreatic or hepatobiliary cancer
Used for diagnosis and evaluation of treatment

Also elevated in

Gastric cancer                   Colorectal cancer
Hepatoma                          Pancreatitis
Gallstones                         Cirrhosis
Cystic fibrosis
Inflammatory bowel disease

Usually not > 70 U/ml in these diseases

CA 125

Cancer antigen 125
Detect ovarian cancer
Elevated in over 80% of women with ovarian cancer
Used for detection, response to therapy, and posttreatment surveillance
Critical value > 65 kU/ml

If detected in body fluids, indicates metastasis

Pleural fluid
Peritoneal fluid

Also elevated in

Cirrhosis                                      Pancreatitis
Peritonitis                                    Endometriosis
Pelvic inflammatory disease
Cancers of genital tract, pancreas, colon, lung and breast

CEA

Nonspecific
Found in variety of cancers

Breast                         Colorectal
Pancreatic                   Hepatobiliary
Gastric                        Sarcomas

Also elevated in

Chronic smokers        Ulcerative colitis
Diverticulitis             Cirrhosis
Hepatitis                    Cholecystitis
Pancreatitis                Peptic ulcer

Not a reliable screening tool
20% of patients with advanced breast or GI tumors do not have elevated CEA
If present in other body fluids (peritoneal, CSF) indicates metastasis to that area

PSA

Screening for prostate cancer and monitoring therapy for prostate cancer and BPH
90% accurate when combined with manual prostate exam
Present in all males, increased with prostate hypertrophy
Normal < 4 ng/dl; > 10 ng/dl highly suggestive of cancer
Predicted PSA – corrects for hypertrophy
             = 0.12 X gland volume (cm3) determined by ultrasound
May be age adjusted to correct for hypertrophy
Draw sample before prostate exam
Prostate biopsy or TURP will greatly elevated PSA – wait 6 weeks

Prostatic Acid Phosphatase

Isoenzyme of acid phosphatase
Less sensitive than PSA
Not elevated in early stage prostate cancer
Elevated when cancer has metastasized beyond prostate capsule, esp. into bone

Acid phosphatase

Also found in seminal fluid and WBC
Investigate alleged rape
Monitor lymphoproliferative diseases
Separate isoenzymes by electrophoresis
Alcohol, fluorides & heparin decrease AP
Androgens & clofibrate increase AP

Alpha Fetoprotein

Extremely high levels diagnostic for hepatoma (> 500 ng/ml)

Other cancers with elevated levels

Testicular                      Ovarian  
Lung                               Lymphomas  
Renal cell                      Breast
Hodgkin’s disease         Stomach                   
Colon

Also elevated in

Chronic active hepatitis
Cirrhosis

Human Chorionic Gonadotropin

In nonpregnant women presence can indicate

Hydatidiform mole                            Choriocarcinoma of uterus
Hepatoma                                          Lymphoma
Germ cell cancers of testes or ovaries

Toxicology

Determine cause of acute drug toxicity
Help monitor drug dependency
Detect presence of illegal substances in body for legal purposes
Especially important in patients with drug overdose or poisoning

Common Blood Toxicology Tests

Acetaminophen                                      Alcohol
Amobarbital                                           Butabarbital
Carboxyhemoglobin                               Glutethimide
Lead                                                       Lithium
Meprobamate                                         Methyprylon
Phenobarbital                                         Phenytoin
Salicylate

Common Urine Toxicology Tests

Amphetamines                                      Alcohol
Barbiturates                                          Benzodiazpines
Cocaine, crack                                      Cyanide
Opiates                                                 Marijuana
Phencyclidine (PCP)                            LSD
Analgesics                                            Sedatives
Major tranquilizers                               Stimulants
Sympathomimetics                                Heavy metals

Carboxyhemoglobin

Critical values > 20%

20-30%  dizziness, headache, poor judgment
30-40% tachycardia, hyperpnea, hypotension, confusion
50-60% coma
>60% death

Treatment is with 100% oxygen and hyperbaric chambers.   

Ethanol

50-100 mg/dl (0.05-0.1%) Flushing, slowing of reflexes, impaired visual acuity
> 100 mg/dl (0.1%)       Considered definite evidence of intoxication in most states
> 100 mg/dl   CNS depression and hypotension
> 300 mg/dl (0.3%) Critical 
> 400 mg/dl  Death frequently occurs

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