Tag: Proteinuria

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UpToDate can be so entertaining, I mean deceptive

I am working on a review of membranous nephropathy and I found this quotation from UpToDate:

A random urine protein-to-creatinine ratio should NOT be used for initial risk stratification, since the relationship between the ratio and 24-hour protein excretion varies widely among patients (show figure 2).

This surprised me. I use the protein-to-creatinine ratio all the time and, though I have found some individuals where it is wildly inaccurate, I had been unaware of any data that showed that to be the case.

I eagerly clicked the link to the figure and this is what I found:

That looks highly accurate to me. Every data point clusters right along the line of identity. I pulled the abstract (alas, no full text from NEJM 1983) and found this conclusions from the authors:

In a study of 46 specimens we found an excellent correlation between the protein content of a 24-hour urine collection and the protein/creatinine ratio in a single urine sample.

I love UpToDate but this is really disappointing. Making a claim and referencing it with data which disproves the claim is disingenuous.

UpToDate, you need to do better.

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Calculating the urinary microalbumin to creatinine ratio

One of my high volume referring doctors uses a lab which does not calculate the microalbumin to cr ratio. It always stops me in my tracks when I see the values.

  1. To convert microalbum and urine creatinine to the useful ratio first make sure both values are expressed as mg/L or mg/ml
  2. Divide the microalbumin concentration by the creatinine concentration
  3. Multiply the resulting ratio by 1,000 to get mg albumin over grams creatinine
For example a patient had the following labs:

Microalbumn urine 5.6 mg/dL

Creatinine urine 91.2 mg/dL

Dividing the albumin by cr gives: 0.061

Multiply that by 1,000 to get 61 mg albumin/g creatinine

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Great case in the office


45 y.o. referred for 4+ proteinuria. Patient is asymptomatic without edema but the FLP shows total cholesterol to be pushing 300. The patient reports for one month he has seen bubbles in his urine. A 24-hour urine showed 2,500 mg of protein on an adequate specimen.

PMHx is significant for gout which has been treated with allopurinol without much improvement. Over the last couple of years he has gone from 100 mg to 300 mg, during this time his uric acid has stayed a midling 7-9 mg/dL. Two months ago he was started on probenecid, a uricosuric agent. This is appropriate as his renal function is great (S Cr of 0.9 in a male who works out).

His physical exam is benign.

No additional relevent data can be gleaned from his labs.

What’s the diagnosis?

Proteinuria due to probenecid. The patient stopped the offending agent and within ten days the U/A showed 1+ proteinuria and the PCR was 0.37.

In the exam room I told him it was a membranous nephropathy but according to this letter to NDT from 2007 the pathology is not typically membranous at all. This jives with the rapid recovery from proteinuria after the medicine is withdrawn.

Here is the mechanism of action of probenecid from UpToDate:

MECHANISM OF ACTION — Competitively inhibits the reabsorption of uric acid at the proximal convoluted tubule, thereby promoting its excretion and reducing serum uric acid levels; increases plasma levels of weak organic acids (penicillins, cephalosporins, or other beta-lactam antibiotics) by competitively inhibiting their renal tubular secretion

Cool case.

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Has anybody seen this?

I have two patients who routinely have significantly lower spot protein to creatinine ratios as compared to 24-hour urine for protein.

The urine electropheresis shows non-specific proteinuria.

  • The first patient is an obese young African American woman with WHO type V lupus nephritis.
  • The other patient is a thin young Caucasian woman with secondary FSGS due to chronic reflux. Her most recent PCR is 1.7, and her 24-hour urine from one week prior is 4.9 g.

Any ideas? What am I missing?