| Course | PA 524 Comprehensive Clinical Module Nephrology & Genitourinary |
|---|---|
| Week | 1 |
| Paper type | Discussion post with two replies |
| Length | About 540 words |
| Format | Discussion post with APA 7 citations |
| School | Chamberlain University |
| Program | Master of Physician Assistant Studies (MPAS) |
| Updated | October 2026 |
Free sample paper for PA 524 Week 1
Week 1 Discussion: Initial Post
Serum Creatinine as the Stand-In for Filtration, Defended for Most Adults and Conceded for a 74-Year-Old Former Machinist Who Lost a Leg and Most of the Muscle That Makes It
Initial Post
I will defend serum creatinine as the everyday stand-in for glomerular filtration, because the body makes it at a fairly steady rate and the kidney clears it mainly by filtration. Creatinine comes from creatine in skeletal muscle, which breaks down at a near-constant daily rate in proportion to muscle mass. It is filtered freely at the glomerulus, is not reabsorbed, and is secreted by the tubules only in a modest amount. So at steady state, the level in the blood rises as filtration falls, and a doubling of creatinine roughly means a halving of filtration (Levey et al., 1988).
A Concession With Somebody in It
The equation was not built for G.H. G.H. is 74, a retired machinist with a below-knee amputation after a crush injury and a weight of 58 kg. With less muscle, G.H. makes less creatinine, so a serum creatinine of 1.1 mg/dL can sit inside the laboratory range while filtration is already reduced. The estimating equations assume an average muscle mass for age and sex, and G.H. is far from average. For G.H., creatinine will overestimate kidney function, and a normal-looking value will be falsely reassuring.
Where Else It Fails
The stand-in also fails when the level is not at steady state, such as in the first days of acute kidney injury, when creatinine lags behind a sudden fall in filtration. It is pushed up by drugs that block tubular secretion, such as trimethoprim, without any change in filtration, and by a large cooked-meat meal shortly before the draw.
Why It Still Earns Its Place
Even with those failures, creatinine is cheap, run on every basic metabolic panel, standardized across laboratories and available years back in most records, which lets a clinician see a trend. For most adults of ordinary build at steady state, the equations built on it are close enough to guide staging and most drug doses. The case for replacing it is strongest in exactly the people the equations misdescribe, and G.H. is one of them.
The Question I Leave Open
Cystatin C is made by nearly all cells and depends much less on muscle. In a large pooled analysis, estimates based on cystatin C, alone or combined with creatinine, predicted death and kidney failure better than creatinine alone (Shlipak et al., 2013). Should G.H.'s kidney function be judged by cystatin C instead, and if the two disagree, which one should guide a drug dose?
Reply to Nadia
Nadia, you chose blood urea nitrogen as your stand-in. Urea is made in the liver at a rate that changes with protein intake, bleeding into the gut and steroid use, and much of it is reabsorbed in a dry patient. Could you name one person in whom urea would mislead you, the way G.H. misleads creatinine?
Reply to Theo
Theo, your post argues that 24-hour urine creatinine clearance is the better measure. It removes the muscle problem, but who collects a complete 24-hour sample correctly? If your patient missed one void, which way would the error push the clearance?
References
Levey, A. S., Perrone, R. D., & Madias, N. E. (1988). Serum creatinine and renal function. Annual Review of Medicine, 39, 465-490. https://doi.org/10.1146/annurev.me.39.020188.002341
Shlipak, M. G., Matsushita, K., Arnlov, J., Inker, L. A., Katz, R., Polkinghorne, K. R., Rothenbacher, D., Sarnak, M. J., Astor, B. C., Coresh, J., Levey, A. S., & Gansevoort, R. T. (2013). Cystatin C versus creatinine in determining risk based on kidney function. New England Journal of Medicine, 369(10), 932-943. https://doi.org/10.1056/NEJMoa1214234
PA 524 Week 1 instructions, in plain terms
The opening post asks you to choose one stand-in for kidney filtration and defend it. Name the stand-in in the first sentence and explain both halves of why it works: where the substance comes from and how the kidney removes it. Then make a concession tied to a specific person, someone whose build, diet or medicines the stand-in was never designed for, and say which way the error runs. Add the other circumstances in which the stand-in fails, such as rapidly changing kidney function. Leave the group a genuine open question, such as whether a different marker should replace yours for that person. Cite sources early in the post rather than only at the end. Reply to two classmates by naming a specific person in whom their chosen stand-in would mislead.
Inside the PA 524 Week 1 example
The post defends creatinine, explaining its steady production from muscle creatine and its clearance mainly by filtration with modest secretion, and cites Levey and colleagues on the inverse relationship at steady state. The concession centers on G.H., a 58 kg retired machinist with a below-knee amputation, whose low muscle mass lets a normal-looking creatinine hide reduced filtration. Further failures follow: non-steady states in acute injury, trimethoprim blocking secretion and a large cooked-meat meal. A section on practical strengths notes cost, standardization and long trends in the record. The open question asks whether cystatin C should judge G.H.'s kidneys, citing Shlipak and colleagues. Replies ask Nadia to name a person in whom urea misleads and press Theo on the error a missed void introduces.
PA 524 Week 1 rubric: what full points look like
The heaviest marks this week go to a defended stand-in with both halves of the argument stated. A post that names a marker without explaining its production and removal loses the largest share. Faculty then look for a concession tied to a real or composite person and a stated direction of error; a general remark that creatinine has limitations earns little. Credit grows with additional failure circumstances that are accurate and specific. The open question is graded on whether it is genuine and answerable. Sources cited early, supporting specific claims, are expected. Replies are marked on whether they challenge a classmate with a concrete person or scenario rather than agreeing. Posts that survey every kidney marker instead of defending one lose points for focus.
PA 524 Week 1 help: mistakes that cost points
Students often lose marks on this post by listing every kidney marker instead of defending one. Share your case and any patient your section described, and your sample would name a single stand-in, explain where it comes from and how it is cleared, and tie its main weakness to a specific person. The other circumstances that break it are added with the direction of each error. A practical paragraph explains why the stand-in remains in use. The open question is framed so classmates can answer it. Replies are written to your classmates' real posts, each pointing to a person in whom their marker would mislead. If your section requires more than two sources, the post adjusts. Treat the model as a check on structure while the argument itself comes from your patient.
Get a PA-524 Week 1 example written to your instructions
Send the discussion question exactly as your classroom posts it, with the reply count and any reference rule attached, and a custom example is written to it and returned inside 24 to 48 hours. The first one is free. If your section has already named the substitute measure it wants defended, say which, and the post is built on that one.
More PA 524 papers and MPAS samples
- PA 524 Week 2: Filtration Estimate Write-up
- PA 524 Week 3: Urinalysis Interpretation
- PA 524 Week 4: Prerenal Versus Intrinsic Brief
- PA 524 Week 5: Volume and Sodium Case
- PA 524 Week 6: Acid-base Disorder Set
- PA 524 Week 7: Urinary Obstruction Brief
- PA 524 Week 8: Renal Dosing Adjustment Table
- PA 522 Week 1: Hormone Pair Discussion Post
- PA 520 Week 1: Exertional Oxygen Claim Post
- PA 518 Week 1: Pretest Likelihood Discussion Post
- PA 516 Week 1: Hidden Eardrum Discussion Post
PA 524 Week 1 questions, answered
Our section wants two replies. What counts as a reply here?
A reply that earns its points does one of three things on this topic: it supplies a second person for whom the chosen substitute misleads, it challenges the mechanism as the original post stated it, or it names a situation where the substitute is fine and explains why. Restating the post with approval attached is the version graders mark lowest, and it takes as long to write.
Can the post use an equation the course has not covered yet?
Yes, provided it is named rather than computed. Week 1 is about the substitution itself, so referring to an estimating formula by name and saying it exists is enough; running the arithmetic pulls in a later week's work and usually crowds out the concession this discussion is marked on. If your instructions ask for a worked figure, send them over and the example includes one.
Does the post need a case, or is it a theory question?
Most versions read as theory and are marked as argument. A case is not required, but one named situation anchoring the concession is the cheapest way to lift a middling post, because it converts a general caveat into something a classmate can test. If your section supplies a scenario, the claim still comes first and the scenario sits underneath it as evidence.
Where can I find a free PA 524 Week 1 sample paper?
This page holds a full PA 524 Week 1 post defending serum creatinine as a filtration stand-in and conceding it for a patient with low muscle mass, with two replies.
Why does creatinine mislead for the patient in the PA 524 Week 1 sample?
An amputation and low weight mean less muscle and less creatinine production, so a normal-looking value can hide reduced filtration.