DHA exam preparation (Dubai) – page 16

Glycogenolysis is the breakdown of glycogen. Glycogenesis is glycogen synthesis, gluconeogenesis makes new glucose from non-carbohydrate sources, and glycolysis breaks glucose down to pyruvate.

A 10–12 hour (9–12 h) fast lets chylomicrons from the last meal clear, so triglycerides and calculated LDL are reliable.

Chylomicrons are made by intestinal cells from absorbed dietary fat and carry it via the lymph into the blood. VLDL carries triglyceride made in the liver.

Isoenzymes are structurally different forms of an enzyme (often from different tissues) that catalyse the same reaction, e.g. CK-MM, CK-MB and CK-BB.

hCG is produced by the trophoblast soon after implantation, and immunoassays for hCG are the basis of pregnancy tests.

CA 19-9 is used mainly for pancreatic (and biliary) cancer monitoring. It is not raised in people who lack the Lewis blood group antigen.

Lithium has a narrow therapeutic range, and toxicity (tremor, confusion, arrhythmia) can occur just above it, so serum levels are checked regularly, usually 12 hours after the last dose.

The first morning urine has been in the bladder overnight, so it is concentrated and best for detecting substances and formed elements present in small amounts.

Some urobilinogen formed in the gut is reabsorbed and excreted in urine, so a small amount (up to about 1 mg/dL, 1 EU) is normal. Strips cannot reliably detect its absence.

The blood pad uses the pseudoperoxidase activity of heme, which is present in hemoglobin (free or in red cells) and in myoglobin.

Crystal formation depends on pH; for example, uric acid crystals form in acidic urine and triple phosphate in alkaline urine, so pH helps narrow the identification.

Squamous cells line the vagina and distal urethra, so large numbers usually mean the sample was not a proper midstream clean-catch collection.

Bacteria double rapidly in urine at room temperature, so an old unpreserved sample can show many bacteria without true infection. Urine should be tested within 2 hours or refrigerated.

Most CSF is secreted by the choroid plexus in the brain ventricles. Arachnoid villi (granulations) reabsorb CSF into the venous sinuses.

Normal CSF is crystal clear and colourless, like water. Cloudiness, blood or yellow colour are abnormal findings.

The needle is inserted below the end of the spinal cord (about L1–L2 in adults), usually at L3–L4 or L4–L5, to avoid injuring the cord.

Dilute (3%) acetic acid lyses red cells and makes white cell nuclei easier to see, so WBCs can be counted in a bloody sample. Saline preserves red cells.

Normal joint fluid is clear, pale yellow and viscous because of hyaluronic acid. Cloudiness suggests inflammation or infection.

Colorectal cancers and large polyps bleed intermittently in small amounts, so testing stool for hidden blood is used as a screening test.

Meconium (fetal stool) gives amniotic fluid a dark green colour and can indicate fetal distress. Bilirubin gives a yellow colour and blood a red colour.