1. B12 deficiency
- Neuropsych signs (~33%, can occur w/ normal CBC): paresthesias, then ataxia with loss of vibration/position, then severe weakness, spasticity, clonus, paraplegia, incontinence, delirium/dementia.
- Homocysteine & MMA: they both need B12 to be converted to breakdown products, so they will increase in cases of B12 deficiency. Sensitivity of both tests are 85-95% sensitive. Homocysteine is less specific, can be elevated in vascular dx, some other processes.
- Anemia in ~75%, macrocytosis in ~80%. Normal CBC does NOT rule out B12 deficiency.
- B12 protien bound & released by acid digestion in stomach, binds IF in jejunum, absorbed in terminal ileum.
- Dietary deficiency rare bc 4 years of stores in liver.
- Old people who don't have stomach acid (atrophic gastritis, PPI, metformin) can have trouble absorbing B12.
- B12 level can be falsely low in folate deficiency, pregnancy, OCPs
- B12 deficiency: when to treat: when B12 is very low, when the B12 is borderline but either Homocysteine or MMA are low.
- Can treat with IM B12, or PO B12-- if you give huge doses, you can overcome even pernicious anemia.
2. Folate deficiency
- Drugs that interrupt the DHFR pathway: methotrexate, phenytoin, sulfasazlaine, alcohol
- People who need extra folate: chronic hemolytic anemia (like sickle cell), pregnancy, increased growth periods -- these people should always be taking folate
- Red cell folate reflects status over 3 months; sens/spec ~70%
3. Anemia of chronic disease
- Iron studies all slightly low, with high ferritin, low RPI
- Common causes: CKD, autoimmune dx, endocrinopathies, cancer, acute/chronic infection
- Cytokines change iron processing
- Hb <8 suggest additional cause
- Look for iron, B12, folate
- Should not be pancytopenic
4. TTP-HUS:
- fever, thrombocytopenia, hemolytic anemia, kidney injury, neuro sx
- w/u with smear, coags to r/o DIC
- tx with plasmapharesis to get off the anti-ADAMSTS13 antibodies
5. When someone walks in with AKI, consider the following first:
- Look at volume status => replenish volume
- Stop NSAIDs and other nephrotoxins
- Obstruction (older male, anticholinergics, urine problems) => bladder scan/straight cath => if the residual volume is high, get a renal u/s then relieve the obstruction
6. Prerenal (low FeNa)
- Dehydration, blood loss
- CHF/Cirrhosis
- NSAIDs
- Vascular - thrombi, severe b/l RAS
7. Intrarenal
- Glomerular: Nephritic syndrome (ie. red cell casts) , nephrotic
- Tubular: ATN from toxins (most common are contrast - muddy brown casts, and post-operative), prolonged hypotension
- Interstitial: 85% caused by meds: NSAIDs, antibiotics, diuretics (thiazides), anticonvulsants, PPIs, penicillins, cipro, 10% from infections (pyelo)
- Vascular
- TTP-HUS: vascular risk factors, DIC, TTP-HUS
8. Post-renal
- Prostate
- Stones
- Cancer obstructing all kidneys
- Neurogenic
- Once you relieve obstruction, there will be post-obstructive diuresis - keep up with IVF
9. Workup:
- Urine dipstick and microscopy
- Urine electrolytes
- Straight cath
10. FeNa/FeUrea 
- FeUrea more sensitive and specific than FeNa in people on diuretics, perhaps in everyone
- FeNa <1%, FeUrea <35% suggestive of pre-renal cause; higher suggest non-pre-renal cause.