Answering your questions on odd urine specific gravities, sendout handling fees, osmotic fragility method, and blood culture contamination rate

Dec. 1, 2001

Edited by Daniel M. Baer, MD

Odd urine specific gravities

Q: In our lab, when we have a specific gravity < 1.005, we check it out on a refractometer and then accept the refractometer results. Recently we have encountered a few specimens with negative glucose and negative protein that give refractometer results > 1.035 not just a little, but a lot. Two recent results were 1.092 and 1.104. Our policy is to dilute the urine with distilled water and repeat the test on the
refractometer. Is there a drug or perhaps something used in x-ray testing that might cause such results? The patients did have radiologic procedures using contrast dyes. We use a Bayer Clinitek 200 for our dipstick testing.

A: When specific gravity readings greater than 1.035 by
refractometer, accompanied by normal specific gravity by reagent strip are encountered, the presence of unusual solutes such as glucose, protein, radiopaque media, or certain drugs should be suspected. 

Since the kidney is only able to concentrate the urine to about 1.035, and refractometer readings correlate with specific gravity of urine only to 1.035, we merely report results as > 1.035. We do not feel that dilution with water is necessary. However, we do attempt to identify the cause of increased readings by other urine findings such as glucose or extremely high protein on the chemical screen, or a patient history of radiographic studies or treatment with drugs that might increase the specific gravity.

The presence of radiographic media may be confirmed by a clinical history of recent radiographic imaging procedures. Organic iodides in radiographic contrast media such meglumine diatrizoate
(Renograffin, Hypaque) may be seen in the urine sediment for a brief time after injection of the dye. The crystals are seen as flat, clear, colorless rhombic plates or rectangles (resembling crystals of cholesterol an extremely rare urine sediment finding).1 They should not be mistaken for cholesterol crystals, the presence of which are a significant pathologic finding. Urine specimens containing radiographic media will also show a delayed, false positive sulfosalicylic acid test for urine protein. This finding may be observed with or without the presence of crystals in the urine sediment. Microscopically, the precipitate in the SSA test tube is unlike the amorphous precipitate seen with precipitated protein. Rather, the precipitate shows crystals, as long slender needles which polarize light.2 

Other drugs causing false positive SSA tests include high levels of penicillin, sulfonamides, or
cephalosporin; Tolbutamine metabolites; and Tolmetin (Tolectin). These should be confirmed by checking the patient history and observing crystals in the SSA precipitate. 

Karen M.
Ringsrud, MT(ASCP)

Assistant Professor
Dept. of Laboratory Medicine and Pathology
University of Minnesota Medical School
Minneapolis, MN


1. Linn J.J., Ringsrud
K.M. Clinical Laboratory Science: The Basics and Routine Techniques, 4th ed. St Louis, MO:
Mosby, 1990, p. 545.

2. Ringsrud K.M., Linn
J.J. Urinalysis and Body Fluids: A ColorText and Atlas. St. Louis, MO:
Mosby; 1995, p. 53-54, 167. 

Sendout handling fee

Q: Can you provide a reference and information about Medicare acceptance of handling charges for sendout testing? We are currently not billing, but incur the cost of sending testing out. How can this be eliminated as a drain on our resources?

A: Medicare has a CPT code for handling fees (99000), but according to several consultants Medicare doesnt reimburse for it. The managers I talked with share your frustration and are absorbing the loss as a nonreimbursed cost of doing business. I am told that other payers do pay a handling fee, and if the account is required contractually to send out specimens, then the sender should have some leverage to negotiate for reimbursement.

Dennis Ernst, MT
The Center for Phlebotomy Education
Ramsey, IN

Osmotic fragility method

Q: We currently use the Dacie method for osmotic fragility, and we are looking for a modified, relatively simple procedure for performing this test. This is not a high volume test for us, but labor-intensive with an already short staff. Is there an easier method?

A: The Dacie method for the determination of osmotic fragility has been the definitive method for the diagnosis of hereditary spherocytosis (HS) for quite some time, but as you point out, it is labor-intensive and also technically demanding.

Therefore you may wish to use several screening procedures that might help to screen out cases not requiring the definitive procedure. For example, the complete blood count which may show only a mild anemia, has a variable MCV which varies depending upon the reticulocyte count. More helpful is the
MCHC, which is increased in one-half to two-thirds of HS patients. HS is the only disease in which the MCHC is elevated. 

Examination of a well-prepared peripheral blood film from a patient with HS reveals many characteristic
microspherocytes, which appear as very deeply stained red cells with decreased diameters and without central pallor.

If these laboratory tests are suggestive and there is a family history of anemia, you still may wish to perform a definitive osmotic fragility test. Treatment for this condition is splenectomy after which spherocytosis persists, but the anemia, if it was present, improves.

A useful discussion of this condition can be found in the noted reference.1

John A.
Koepke, M.D.

Professor Emeritus of Pathology
Duke University Medical Center
Durham, NC


1. Hansen,D.M. Hereditary anemias of increased destruction. In Clinical Hematology. Principles, Procedures and Correlations
Second Edition. Stiene, Martin E.A., Lotspeich Steininger, C.A. &
Koepke, J.A. Lippincott, Philadelphia, PA 1998.

Blood culture contamination rate

Q: My question pertains to blood culture contamination rates. I read with great interest the article in the May 2000 issue about this topic. We have been struggling with a contamination rate >3.0 percent.

This facility is a 42-bed hospital with a 120-bed nursing home attached. We collect from about 60 to 190 blood cultures each month and our contamination rate varies from 3.2 percent to 5.1 percent.

The average age of the patients with contaminated blood cultures is about 75 years old. I have found no trends associated with who collected the culture (nursing vs. lab staff), department collected in (emergency room, outpatient, inpatient). 

Our medical director feels that the small total number of blood cultures collected here and the elderly population that we serve are skewing our results. I wholly agree with this; however, administration is always looking for performance improvement measures and continues to insist that we improve our contamination rate.

Are there any guidelines for small hospitals serving primarily elderly patients? Are there published thresholds for a facility such as mine? Do you have any suggestions regarding this issue? 

A: The article in the May 2000 issue of MLO is an up-to-date review of the blood culture contamination problem.1 In addition to this, CAP Today recently published a long article about preventing blood culture contamination.2 

Your administrator is correct in being concerned about the blood culture contamination rate. Several studies have shown that a false positive blood culture increases hospitalization by an average of five days and increases pharmacy and laboratory costs by more than $1,000. This can cost a hospital $4,000 to $5,000 in additional expenses.

The CAP Q-Tracks program recently published data from 155 institutions showing an average overall blood contamination rate of 2.94 percent. Analysis of these data show that the use of tincture of iodine as a skin disinfectant and collection of higher blood culture volumes were correlated with a lower contamination rate.

Skin flora cause contaminated cultures. Tincture of iodine is a more effective skin disinfectant than
povidone-iodine (Betadine). Disinfection technique is important prior to
venipuncture. First, the skin should be cleaned for one minute using 70 percent isopropyl alcohol. Next, a 2 percent tincture of iodine is applied and allowed to dry for two minutes before phlebotomy. Complete drying of the disinfected area is important.

Contamination is reduced if blood is collected directly into the culture bottle rather than using an intermediary syringe and needle. Filling of the bottle to its recommended volume is also important.

The training and experience of individuals who collected blood culture samples has a direct effect on the contamination rate. Those institutions with the best contamination rates have dedicated blood culture collection teams. The important factor here is that the team members are well trained and experienced.

Tracking the contamination rate and feedback to phlebotomists also reduces contamination rates. Some hospitals maintain data on contamination rates for each person who collects blood culture specimens. This information is reported back to the individual. In one hospital, this feedback was correlated with a decrease in contamination from 2.65 percent to 1.4 percent.

As for what contamination rate to expect for a small hospital with elderly patients, we are not aware of data correlating hospital size or patient age with contamination rates. A CAP Q-Probe exercise involving 640 hospitals came to the same conclusions as the Q-Tracks study, but did not study the variables of age or hospital size.3 One might think that large academic medical centers may have higher rates because of lack of control and training of the many care givers who collect blood cultures.

Daniel M. Baer
Professor Emeritus of Laboratory Medicine
Oregon Health Sciences University
Portland, OR


1. Ernst, D., Controlling blood culture contamination rates. MLO May 2000. p 36-47.

2. Paxton, A., Nipping contamination in the blood. CAP Today May 2000, 14:1 and 56-70.

3. Schifman, R.B., Strand,
C.L., Meier, F.A. and Howanitz, P.J. Blood culture contamination: A College of American Pathologists Q-Probe study involving 640 institutions and 497,134 specimens from adult patients. Arch Pathol Lab Med 1998;122:216-221.

Daniel M. Baer is professor emeritus of laboratory medicine at Oregon Health Sciences University in Portland, OR, and a member of MLOs editorial advisory board.

2002 Nelson Publishing, Inc. All rights reserved.