interpreting laboratory tests and results

Dilutional ↓ in albumin, ↑ in ALP (placental), ↑ cholesterol

how are labs typically different in pregnancy?

Dehydration → ↑ BUN, Hct; Overhydration → dilutional ↓

how can dehydration and overhydration contribute to lab findings?

↑ total protein, K⁺

how can tourniquet use alter lab findings?

sensitivity

Ability to detect disease when it's present (true positive rate)

-rules out disease when negative

TP / (TP + FN)

formula for sensitivity

specificity

Ability to identify those without disease (true negative rate)

-rules in disease when positive

TN / (TN + FP)

formula for specificity

positive predictive value

Likelihood that a positive test = true disease

-affected by prevalence

TP / (TP + FP)

equation for PPV

negative predictive value

Likelihood that a negative test = no disease

TN / (TN + FN)

equation for NPV

(TP + TN) / (TP + TN + FP + FN)

equation for accuracy

Liver disease (cirrhosis, hepatitis)

cause of decreased synthesis of albumin

Nephrotic syndrome, protein-losing enteropathy, severe burns

-albumin lost via urine, stool, or exudate

causes of increased loss of albumin

decreased amino acid availability

how does malnutrition decrease albumin levels

Overhydration, IV fluids

causes of hypoalbuminemia due to hemodilution

Clinical consequence: ↓ oncotic pressure → edema, ascites, delayed drug binding.

consequences of hypoalbuminemia

low albumin

effect of infection, trauma, and sepsis on albumin levels

↑ ALP + ↑ calcium/phosphate, normal GGT

findings that the source of increased alk phos comes from bone

GGT (gamma glutamyl transferase)

Test given for possibility of alcohol abuse

Paget's disease, fractures, osteomalacia/rickets, bone metastases, hyperparathyroidism

causes of bone source elevated alk phos

-Cholestatic pattern; biliary obstruction or intrahepatic cholestasis

-↑ ALP + ↑ GGT + ↑ bilirubin

key clues indicating elevated alk phos from a liver souce

Gallstones, biliary atresia, cholangitis, primary biliary cholangitis, drug-induced cholestasis

causes of elevated alk phos from a liver source

alkaline phosphate

placental isoenzyme, normal to be elevated in pregnancy

elevation

may be post-prandial ________ of alk phos

-benign, transient

If ALP ↑ and GGT normal → bone origin.If both ALP ↑ and GGT ↑ → hepatic/biliary origin.

how does GGT help determine source of alk phos elevation?

Salivary gland inflammation (mumps), renal failure (↓ clearance), perforated ulcer, bowel obstruction, ectopic pregnancy

non-pancreatic causes of elevated amylase

lipase

elevation of _______ found in Acute pancreatitis (↑ earlier & remains elevated longer), pancreatic duct obstruction, pancreatic carcinoma

Renal failure, bowel infarction, perforated viscus, celiac or peptic ulcer disease

non-pancreatic causes of elevated lipase

acute pancreatitis

Both amylase + lipase ↑ = likely

lipase >3x ULN

lipase level most specific for pancreatitis

salivary or GI causes

increased amylase alone is indicative of

↑ Ca, ↓ phosphate, ↑ PTH

lab findings of primary hyperparathyroidism

PTHrP secretion (SCC), bone lysis (myeloma, metastases)

mechanism of malignancy related hypercalcemia

↑ Ca, ↓ PTH

lab findings of malignancy related hypercalcemia

↑ Ca, ↑ phosphate, ↓ PTH

lab findings associated with vitamin D intoxication

thiazide diuretics

-reduce renal calcium excretion

diuretic type most likely to cause hypercalcemia

↑ 1-α hydroxylase → ↑ vit D activation

how do granulomatous dieseases (sarcoidosis, TB) contribute to hypercalcemia?

increased bone resorption

↑ Ca, ↓ PTH

how does immobilization lead to hypercalcemia

↓ Ca, ↑ phosphate, ↓ PTH

lab findings of hypoparathyroidism

↓ Ca, ↓ phosphate, ↑ PTH

lab findings of vitamin D deficiency

↓ 1,25-D synthesis, phosphate retention

results in : ↓ Ca, ↑ phosphate, ↑ PTH (secondary hyperPTH)

how does CKD contribute to hypocalcemia

secondary hyperparathyroidism

Hypocalcemia of chronic kidney disease

hypocalcemia and hypomagnesemia

impaired PTH secretion/action results in

low calcium, normal phosphate

how does acute pancreatitis affect calcium levels

hypocalcemia due to citrate binding of Ca2+

how does sepsis/massive transfusion effect calcium levels

Hypercalcemia: "Bones, stones, groans, and psychiatric overtones."

Hypocalcemia: Chvostek's sign, Trousseau's sign, tetany, paresthesias, seizures

symptoms of hyper vs hypocalemia

DNA synthesis, myelin formation

functions of vitamin B 12

Decreased intake: vegan diet, malnutrition Malabsorption: pernicious anemia (↓ intrinsic factor), gastric bypass, ileal resection, Crohn's, chronic pancreatitis

Competition: Diphyllobothrium latum (fish tapeworm), SIBO, metformin use

causes of vitamin B12 deficiency

Macrocytosis (↑ MCV), hypersegmented neutrophils, ↑ methylmalonic acid & homocysteine, neurologic symptoms

labs/findings associated with B12 deficiency

DNA synthesis

function of folate

Decreased intake: poor diet, alcohol use, elderly

Increased demand: pregnancy, hemolysis, malignancy

Drugs: methotrexate, phenytoin, TMP-SMX

causes of folate deficiency

methotrexate, phenytoin, TMP-SMX

drugs that can cause folate deficiency

↑ MCV, hypersegmented neutrophils, normal methylmalonic acid, ↑ homocysteine, no neuro deficits

key lab findings of folate deficiency

B12: ↑ methylmalonic acid & homocysteine

folate: normal methylmalonic acid, ↑ homocysteine

methlmalonic and homocysteine findings associated with B12 vs folate deficiencies

B12 → Brain (neuro symptoms) + "12 months to store" (large hepatic stores).Folate → "4-letter vitamin" → "4 months to deplete" (shorter stores).

when do manifestations of B12 vs folate deficiency present

Bacterial infection, inflammation, corticosteroids, stress reaction, myeloproliferative disorders

elevated neutrophils are indicative of

Aplastic anemia, chemo, sepsis (late), autoimmune neutropenia, hypersplenism

low neutrophils is indicative of

Viral infections (EBV, CMV, pertussis), CLL

causes of elevated lymphocytes

HIV, steroids, chemotherapy, radiation

causes of low lymphocytes

Chronic infections (TB, syphilis), autoimmune disease, malignancy

causes of elevated monocytes

Aplastic anemia, glucocorticoid therapy

causes of low monocytes

Neoplasia, Allergy, Asthma, Collagen vascular disease, Parasites (especially helminths)

causes of elevated eosinophils

Steroids, Cushing's syndrome, stress

causes of low eosinophils

Myeloproliferative disease (esp. CML), hypothyroidism

causes of elevated basophils

stress reactions, hyperthyroidism

causes of low basophilss

Bone marrow failure (aplastic anemia, chemo, radiation), marrow infiltration (leukemia, myelofibrosis), B12/folate deficiency, liver disease (↓ thrombopoietin)

common causes of decreased production of platelets

Immune-mediated (ITP, SLE, HIV), DIC, TTP/HUS, heparin-induced thrombocytopenia (HIT), sepsis

common causes of increased destruction of platelets

increased destruction of platelets (ITP, SLE, DIC, TTP)

decreased platelets with elevated retic platelets indicates

sickle cell, portal HTN, cirrhosis

-results in thrombocytopenia

causes of splenic sequesteration

no platelets in stored PRBCs

how come a massive transufion can result in thrombocytopenia

Idiopathic Thrombocytopenic Purpura (ITP)

large platelets + thrombocytopenia on peripheral smear indicates

TTP or DIC

low platelets + schistocytes on peripheral smear indicates

Infections, autoimmune (SLE, RA, temporal arteritis), malignancy, pregnancy, anemia

causes of increased ESR

↑ fibrinogen or immunoglobulins → RBCs form rouleaux → faster sedimentation

pathophys of increased ESR in relation to infection, inflammation

Polycythemia, sickle cell anemia, microcytosis, leukocytosis, CHF

causes of decreased ESR

Altered RBC shape or ↓ plasma proteins prevent rouleaux

how do anemias contribute to decreased ESR

Tube angle, temperature, anticoagulant use

extrinsic factors affecting ESR

ESR

nonspecific but useful for monitoring inflammation over time (e.g., temporal arteritis, PMR).