How can you differentiate acute from chronic renal failure? Explain this in terms of history, physical examination and laboratory tests.
In terms of history, one must determine whether previous serum creatinines are available or if there is any history of any systemic diseases that may be associated with renal involvement. Often, one must take the time to call other physicians or hospitals to get old creatinine values.
When it seems that one is dealing with acute renal failure, then there needs to be an assessment for pre-renal, renal, or post-renal causes.
On physical examination, one should look for evidence of a pre-renal cause of renal insufficiency. Hypovolemia would be suggested by features of decreased extracellular fluid volume such as a low JVP, dry mucous membranes or postural tachycardia, or hypotension. Pre-renal disease can also be due to conditions such as congestive heart failure or cirrhosis, so one should also perform a careful cardiac exam and look for stigmata of chronic liver disease.
Post-renal failure can be seen in bladder outlet obstruction, so one could feel for a palpable bladder. Intrinsic renal disease can develop acutely due to systemic disease with renal involvement. One can look for features of some of these systemic conditions which might include rashes, active joints, alopecia, oral/nasal ulcers, peripheral neuropathy, or a murmur from endocarditis.
In terms of lab data, urinalysis is critical. One may see casts that will helpful in terms of diagnosis: RBC casts for glomerulonephritis, WBC casts in acute interstitial nephritis, and heme granular casts in acute tubular necrosis. In chronic renal disease, one may see waxy orbroad casts.
Chronic renal failure may also be associated with anemia, metabolic acidosis, hypocalcemia, and hyperphosphatemia. These may not be entirely reliable; however, as anemia can develop acutely in patients with conditions such as lupus or vasculitis, and hypocalcemia/hyperphosphatemia can be seen in conditions such as tumour lysis syndrome.
On ultrasonography, small kidneys with cortical echogenicity would suggest kidney disease is chronic. If kidney size is preserved this might suggest acute renal failure,though some diseases of the kidney are associated with preservation of renal size (examples include diabetic nephropathy and amyloidosis).