The respiratory and metabolic systems compensate for pH disturbances caused by acidosis or alkalosis. Arterial blood gases (ABG) determine pH, oxygen, and carbon dioxide levels. Interpretation involves identifying pH alterations and their respiratory or metabolic origins. Compensation mechanisms maintain homeostasis. Venous blood gases can be an alternative to ABG in certain conditions.
Human Chorionic Gonadotropin (hCG): Internal Medicine for the Ignorant
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Human Chorionic Gonadotropin (hCG): Internal Medicine for the Ignorant
The clinician who does not appreciate his own ignorance is most dangerous
R. van Zyl-Smit, MD
hCG levels can be elevated with cancers of the uterus, GI tract, and renal system, and will be elevated during pregnancy including multiple birth pregnancy and hydatidiform molar pregnancy.
All are correct.
Human Chorionic Gonadotropin (hCG)
hCG, human chorionic gonadotropin, is a hormone produced by the placenta during pregnancy. Think back to your biology or anatomy and physiology course(s) and recall the chorionic plexus – that beautiful network of blood vessels where placenta meets uterine wall that acts in protection to the fetus similar to the blood-brain barrier and, as important, allows the exchange of fresh blood from mother for old blood from fetus. This Greek word chorion means literally “the membrane around the fetus” and it produces this human chorionic gonadotropin (tropins are hormones). Small amounts of HCG are produced by the pituitary gland naturally, but these amounts typically do not register on a pregnancy test.
hCG has two chains, alpha and beta. We measure the beta chain in pregnancy as it has more to do with the function of the hormone. hCG can be elevated outside of pregnancy, and this is a key clinical pearl. Causes of increased hCG outside of pregnancy include ovarian cancer, bladder cancer, pancreatic cancer, stomach cancer, lung cancer, and liver cancer. In pregnancy, hCG can be elevated during multiple birth, chorionic carcinoma, and hydatidiform molar pregnancy.
Qualitative hCG tests are either positive or negative (hCG is detected past a certain threshold, or it isn’t). Quantitative hCG tests are typically considered positive at levels greater than 2 mIU/mL (milli-international units per mL). During pregnancy, hCG levels tend to double every day, peaking at around 10 weeks gestation and then declining.
FUN FACT: Two German scientists, Aschheim and Zondek, discovered hCG in 1928 when analyzing urine samples from pregnant women. They developed the A-Z test for pregnancy, which was 98% accurate, and consisted of injecting a woman’s urine into a mouse and then dissecting the rodent to see if it had gone into heat (a positive sign for pregnancy). In the 1930’s, the Xenopus pregnancy test was developed by Dr. Georgeanna Jones and consisted of injecting a woman’s urine into an African clawed toad. If the woman was pregnant, eggs would begin to grow in the frog’s lymph sac after just a few hours. Thankfully, we developed tests in the 1960’s that were immunologic, so we only had to rely on injecting animals with human urine to determine pregnancy for about 40 years.
Internal Medicine for the Ignorant
This article is an excerpt from our upcoming course, Internal Medicine for the Ignorant, a course designed for everyone involved in clinical practice that covers 11 body systems, 65 internal medicine diagnoses and their management, as well as over 50 of the most common lab tests and their interpretation and clinical application. You’ll learn about the history of modern-day labs too!
Scheduled Release: November 2024
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