How do laboratory specialists advise clinicians concerning the use and interpretation of renal tests?

Abstract

Background. The aim of this study was to elucidate how laboratory specialists advise clinicians concerning renal parameters and to compare their advice with guideline recommendations. Methods. A questionnaire was distributed to laboratory specialists in Norway and The Netherlands together with two case histories from a primary health-care setting and one from a hospital setting, simulating questions from clinicians. The investigations that laboratory specialists suggested were compared to a test panel that was predefined based on clinical practice guideline recommendations (the ‘recommended test panel’). The critical differences between two test results (creatinine, estimated glomerular filtration rate [eGFR] and albumin/creatinine ratio [ACR]) and the anticipated precision of the MDRD equation were evaluated. Results. Fifty-two of the 100 laboratory specialists responded, and most of these were regularly contacted by clinicians to discuss laboratory results. Less than 30% would suggest using the recommended test panel to evaluate renal function in the two primary-care patients. For creatinine and eGFR, median changes stated to signal improvement or deterioration in renal function (creatinine: −14% and +14%, respectively; eGFR: + 18% and −13%, respectively) were similar to what could be calculated using information on analytical and within-subject variation from the literature. There were variable critical differences for the ACR results (median values of −50% for improvement and + 67% for deterioration). Only 23% of the participants would recommend a gold standard clearance examination for a patient who was to undergo nephrotoxic chemotherapy. Conclusion. Questions from GPs about renal parameters are answered differently by laboratory specialists, and adherences to guideline recommendations are low on some issues.

Key words::

• Albuminuria
• clinical chemistry
• chronic kidney disease
• creatinine
• glomerular filtration rate
• questionnaire

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the article.

Appendix

The questionnaire

Patient 1

A GP calls the laboratory and asks for your advice regarding a 60 year old man who has visited for a routine check of hypertension. The patient's blood pressure was 155/94 mmHg, and he had no other chronic diseases. His GP has obtained the following results from the laboratory; s-creatinine 119 μmol/L (60–105 μmol/L), estimated GFR 54 mL/min/1.73m².

The GP asks you:

1A. Based on this laboratory result, does the patient have chronic kidney disease?

Yes

No

Maybe, and further testing would be necessary; please specify what laboratory test(s) you would recommend to further evaluate if the patient has chronic kidney disease?

______________________________________________________________

1B. The GP tells you that s-creatinine/eGFR will be repeated in 4 months and asks; how large a difference do you think is necessary between the first and second results to denote (95%CI);

– a deterioration in renal function;

s-creatinine should increase to _____μmol/L

eGFR should decrease to ______ ml/min/1.73m2

– an improved renal function;

s-creatinine should decrease to _____μmol/L

eGFR should increase to ______ ml/min/1,73m2

(Note! Exact values above 60 mL/min/1.73m² may also be denoted)

Patient 2

A GP calls you and asks how to evaluate if a 57 year old male, who was diagnosed with type 2 diabetes 2 years ago, has developed diabetes associated renal disease. He has not been tested yet, except with an ordinary urine dipstick test, which was negative. You recommend that the patient should provide morning urine to be analysed as an albumin/creatinine ratio (ACR) analysis. The GP is not very familiar with this test and its interpretation.

He asks you:

2A. If one positive test result is obtained, is that sufficient to diagnose renal disease?

Yes(please proceed to question 2C)

No (please answer question 2B)

2B. If no, what test(s) would you recommend to confirm or exclude renal disease?

Specify _____________________________________

Imagine the case that the patient has an ACR analysis and that a result of 15 mg/mmol creatinine is achieved. A new test is obtained one year thereafter;

2C. How large a difference do you think is necessary between these two ACR results to denote a significant (95%CI):

– deterioration in the patients renal function:

ACR should increase to _____ mg/mmol creatinine

– improvement in the patients renal function:

ACR should decrease to _____mg/mmol creatinine

Patient 3

A colleague in the oncology department calls you and asks about a 57 year old female patient with a malignant disease. Her BMI is normal; 22 kg/m². s-creatinine is 84 μmol/L (45–90 μmol/L) and eGFR > 60 mL/min/1.73m². She will receive treatment with a highly nephrotoxic cytostatica and it is recommended to monitor her renal function during the whole treatment.

The Oncologist asks by which test(s) he should monitor her renal function?

3A. What test(s) would you recommend?

___________________________________________________

3B. When should the test(s) be repeated for monitoring her renal function during the treatment with cytostatica? (please specify for each test if more than one);

Before every cycle (specify the test(s)) _______________________________

Before every second cycle (specify the test(s)) _________________________

Before every third cycle (specify the test(s)) ___________________________

Testing should be performed at other time interval, please specify; _________